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This unit has already saved me $115 - what my car's dealership charges to read and reset the check engine light in my car.

It has also helped me to become a much more fuel efficient driver, and is a fun addition to the gauges and dials in my car.

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ScanGauge II with X-gauge Review

Lots of fascinating - and money saving - information for the driving enthusiast

The small ScanGauge can be mounted just about anywhere around the driver's position in your car.

Although, please note, the position illustrated here is not recommended - it requires you to take your eyes too far off the road to look at it (but it looks good in the promo photo!).

This promo picture shows the ScanGauge displaying water temperature, ignition advance, rpm's, and incoming air temperature.  Many other types of information can also be displayed.



Here's a great device that is useful (and fun) in a number of different ways.

It may save you money by telling you why your 'Check Engine' light is on (and enabling you to turn it off by yourself if you choose).

It can help you save money a different way by giving you a range of information about your vehicle's fuel economy, helping you to modify your driving style for most economic benefit.

And it can give you a lot of information about the vehicle's engine and operation, together with a comprehensive set of 'trip computer' type functions.

The unit is moderately priced ($159.95 on Amazon) and very easy to install.

Recommended for gadget and driving enthusiasts.

An Explanatory Introduction about OBDII and what the ScanGauge can do

Did you know your car has a computer inside it that is continually monitoring, managing, and even recording many different pieces of data to do with the operation of the engine and your driving of the vehicle?

Much of what this computer does occurs in the background, and you never really need to know about its operation.  It is adjusting the mixture of fuel and air that goes into the engine, advancing/retarding the ignition timing, and generally optimizing the engine's operation for maximum efficiency.

It is also quietly monitoring anywhere from a dozen to many dozens of different functions and features in the engine system, and in particular, in its emission control systems, looking for problems or failures.  If it spots any such issues, it will typically turn on your 'Check Engine' light, which sooner or later will guilt you into taking your car to the dealership and having it diagnosed and repaired.

The most interesting part of this computerization is that, per US federal law, all cars manufactured in and after 1996 must have an output port to allow for anyone to connect a diagnostic or other display/monitor/analyzer to the computer to read and track its functioning.  This output port must be in the passenger compartment and relatively close to the steering wheel.

The same requirement generally applies to Canadian vehicles too, and European vehicles (in Europe) also have a similar specification.


This requirement is called the On Board Diagnostics 2 standard (usually abbreviated as OBDII or OBD-II or OBD II or, less commonly OBD2).  It is given the number 2 because there were a couple of earlier semi-standards partially adopted by some vehicle manufacturers, generally called the OBD I and OBD 1.5 standards.

Implementation of the OBDII standard had started prior to the 1996 mandate (indeed, the first car with a computer came out in 1975, with increasingly sophisticated car computers being installed during the 1980s and early 1990s), so if you have an earlier model year car, it may have an OBDII connector block and may provide data in one of the several OBDII compatible modes.

The OBDII standard is a combination of a specification requiring a particular size and shape of physical data connector to be present in the car, together with the ability of the data connector to provide access to the car's computer system(s), which are, for some key things, expected to communicate in a semi-standard manner.

Beyond this 'standard' there are a number of different methods that the computers can provide the data to a connected monitoring device, and the data itself is not necessarily the same for all makes and models of vehicles.

How to use the OBDII data

Devices that can read and monitor the data stream from your vehicle's computer system(s) (your car might have multiple computers, or perhaps just one) can do one or more of several different things.

  • They can detect and alert you to engine problems - giving you more detailed information when the Check Engine light illuminates.

  • They can be used to reset (ie turn off) the Check Engine light, something you might choose to do if you decide the underlying reason for the problem is unimportant and not requiring immediate action.

  • They can provide instantaneous reporting on various engine operating parameters, ranging from vehicle speed to engine workload, from engine temperatures to fuel consumption.

  • They can also be used for 'trip computer' measuring of such things as average miles per gallon since last reset, average/maximum speed, distance traveled, time elapsed, and so on.


Some car manufacturers have delighted in attempting to make their data as difficult to understand and decode as possible; so as to require you to get your vehicle serviced at their dealer franchise facilities rather than at any generic garage/workshop.  But most auto manufacturers have settled into one of several different methods of data presentation, and in addition to their own proprietary data readers, it is increasingly common to find generic data readers that can retrieve and display basic data from most if not all modern vehicles.

The one remaining point of confusion can be that after successfully retrieving and decoding a piece of data, one has to then understand what it means.  It is all well and good to determine that the reason your Check Engine light is on is due to trouble code P0172, but if you don't know what P0172 means, you're not really much better off than you were before.

Fortunately we have the internet to thank, yet again, for the proliferation of a number of good websites (links below) that will tell you the detailed meaning of many/most of the codes from most of the vehicle manufacturers.  So, the world wide web is not just an excellent place for playing online casino and other virtual games - it can really help motorists too.

Lemur SafeDriver

One other device that makes use of the OBD-II data port and data stream is the Lemur SafeDriver unit.  This very moderately priced unit ($70 list, $56 street) is an elegant and easy way to monitor someone's driving.  Please see our full review for more details.

The ScanGauge II

The ScanGauge II is one of the most reasonably priced units that can be attached to your vehicle's OBDII port and which can be used for all the four purposes listed above.

It is full featured and works with almost all vehicles and the various different methods they have of presenting data to the OBDII port, including the latest CAN specification (an enhancement of the earlier OBDII specification).

The ScanGauge II - What You Get

The ScanGauge II is simply packaged inside an attractive cardboard box, and is easily opened.

Inside the box is the unit itself, a small manual, a connecting cable, and two sets of male/female adhesive Velcro pieces for you to use in mounting the unit within your vehicle.

The ScanGauge itself measures 4.8" x 1.5" high and is about 1" deep.  It requires a single cable connection, and very thoughtfully, is designed with a connector both on the back of the unit and on the side of the unit, giving you more flexibility in terms of where and how you locate the unit and run the cable between it and the car's OBDII data port.

The connecting cable is 6' long, and has the proper plug at one end to connect into your vehicle's OBDII port, and an RJ45 type connector to plug into the unit at the other end.  This has always been long enough in the various vehicles I've had my unit (remember that part of the OBDII specification requires the port to be located close to the driver's area of the vehicle).

The small manual measures 4" x 5" and has has 32 pages of information inside.  It is fairly basic in terms of layout, but is well written and easy to follow.

Best of all, the unit is so easy and simple to understand and use you'll soon find you don't need to refer to the manual much (other than to remind yourself what some of the gauges are for!).

The unit requires no batteries or separate power connection.  In a manner similar to a USB connection, it draws the power it needs through the OBDII cable and from the vehicle.  This does mean that it only works when the vehicle is switched on, but, if you think about it, there's not much you'd want to use an engine monitoring unit for when the engine is switched off!

The unit comes with a 30 day money back guarantee and a one year warranty.

Installing the ScanGauge II

Installing it was very quick and easy.  The hardest part is sometimes finding where the OBDII port is - some vehicles place this in a discreet and non-obvious location, other vehicles have it clearly visible once you know what you're looking for.

The first time, I simply called up my dealership and asked them where the port was, and the service writer was able to immediately tell me exactly where to find it.

The most important part of installing the unit is choosing were to put it.  I got it wrong the first time, because I wasn't sitting in my normal driving position while moving around finding somewhere to place it, and what looked like a good place when I was sitting up and forward ended up being obscured by the steering wheel when I was in my normal driving position.  Ooops!  Fortunately the velcro adhesive hadn't yet fully 'cured' (ie set) so I quickly pulled it off the dash and moved it somewhere else that worked better.

The velcro adhesive installation method works only moderately well.  The unit itself is very light (it weighs 2.6 ounces) so this provides a perfectly secure mount.  But it means when you push a button on the front of the unit, the unit rocks back on the velcro, and it also limits where you can place the unit - if you have a sloping dash, the slope might make the unit face in the wrong direction.  On the other hand, a unit attached by velcro is less obvious from the outside, and therefore less likely to attract the unwanted attention of car prowlers.

It is possible to have the velcro mounting on either the bottom, back, or top of the unit, giving you more flexibility.

Even so it would be nice to have a windshield mount as well, to give more flexibility in placement and to provide a more solid mount for when pushing the buttons.

Then I simply ran the cable from the OBDII port to the unit, squeezing it into craps and gaps in the dashboard trim, and, within literally a very few minutes of starting the process, the unit was installed and operational.

Get a second data cable

Here's a useful tip - buy a second data cable.  That way, if you plan to use the unit primarily in your main vehicle, but secondarily in other vehicles, and sometimes use it in friends' vehicles too when helping them diagnose and turn off their Check Engine lights (you'll be amazed how many people will ask you to connect to their car when they discover you can test and reset their Check Engine light!), you don't need to disconnect and unroute the cable you've installed in your main vehicle.  You simply remove the unit off its velcro base, unplug the cable from behind the unit, and off you go to the other vehicle.

This makes it easy and simple, and even easier and simpler when you return it back to your main vehicle.

A second data cable lists for $19.95 and costs $12.95 from Amazon.

Calibrating the ScanGauge II

Much of what the unit does is instantly ready as soon as you connect the unit to your vehicle, and is as correct as the data it is receiving from your vehicle's computer system, with no need for calibration or adjustment.

But if you want to get accurate data on speed, distance, and fuel usage, you'll need to calibrate the unit.

Calibrating for Speed

This is very simple.  To calibrate for speed, you drive your vehicle at a known speed and then switch the unit to display what it thinks is your current speed.  If the unit is wrong, you simply push an Up or a Down button until you get it showing the correct speed.

Here's a tip when calibrating the speed.  Drive your vehicle as fast as is legal and safe, because a small change in speed displayed is a finer adjustment at higher speed than if you are going very slowly.  Any sort of speed measuring/calculating is probably never more accurate (or displayed more accurately) than perhaps 1 mile per hour.  So, if you are calibrating at 10mph, a +/- 1 mph differential is a +/- 10% factor, but if you are going at 70mph, that 1 mph differential is now less than a 1.5% factor.

How to drive at a known speed?  Don't trust your car's speedometer.  It may be using the same data the Scan Gauge is using, and perhaps imperfectly displaying it on an analog dial.

The most accurate speed measurement device is a GPS.  If you don't have one, see if you can borrow a friend's unit, or drive alongside him if that is not possible.  Or, with good GPS units these days costing $200 or less, maybe it is time to get yourself a GPS unit too!

If you can't calibrate your speed, don't worry.  The unit is probably within a few percent of being exact anyway.

Calibrating for fuel economy

This is a bit more complicated, but well explained in the manual.  Basically, you fill your tank with gas, reset the fuel usage meter in the unit, then drive until the tank is more or less empty, then compare the fuel that you actually pump into the vehicle with the fuel the gauge thinks you've used, and, same as with setting the speed calibration, you then adjust the amount the gauge thinks you've used to reflect the reality of how much fuel you actually pumped into your car.

That's the theory of calibrating your fuel usage.  But the practicalities are not quite as optimum as they are for calibrating the speed setting.  To be kind, normal gas station fuel pumps aren't always 100% accurately calibrated - I know this for a certain fact because I've sometimes filled my car with gas, and found, to my astonishment, that the pump shows I've put maybe half a gallon of gas more into my tank than its maximum rated capacity, with the tank having some gas already in it when I pulled up to the pump.

In addition, different pumps shut off at different points, so there's always a tenth of a gallon or so of imprecision at determining the same fill level as well as any error in the pump measuring how much gas it is actually dispensing.

So what I do is I 'average' a series of fillups.  The first time, I set the gauge to exactly the number the pump tells me.  The next time, I adjust the gauge to halfway between what it thinks and what the pump says, and then I make a series of smaller adjustments until it seems the pump amount is close to the amount shown on the unit, sometimes a bit high and sometimes a bit low.  You'll probably end up with something that is accurate to within a few percent.

Fortunately, getting this absolutely exact is not very important.  The key thing remains unchanged - whether the absolute numbers are exact or not, a higher mpg figure is always better than a lower one!

Throttle Position Zero setting and other vehicle specifics

Setting the throttle zero position is another very simple trivial thing that you probably don't even need to worry about.

You can also set some parameters like the capacity of your fuel tank (if you want to use the unit's calculations for amount of fuel remaining and likely distance you can travel on it - not something we recommend you rely too closely on) and a few other things (like if your vehicle uses gas, diesel, or is a hybrid), for which the defaults seem to be perfectly fine most of the time.

If you want to be obsessive (like I was!) read the short section in the manual and follow it to get everything exactly right.  But the default setting seems to work perfectly for most vehicles and applications.


Note that once you've calibrated the unit, it remembers its settings, even when it loses power.  And, if you switch the unit from one vehicle to another, you'll need to recalibrate it for the new vehicle.

But, of course, if you're just using it for its Check Engine diagnostics, you don't need to bother about recalibrating the unit's measurement of speed and fuel consumption.

If you are going to be using it in a couple of different cars, you should write down the calibration settings for each vehicle so you can just apply them directly rather than needing to go through the full process of recalibrating each time you swap the unit over.

How the ScanGauge has Saved me Money

My Scan Gauge, which I've had for only a month, has already saved me (and my friends!) its purchase price ($160) and more besides.

Check Engine light savings

Firstly, the thing that encouraged me to buy it was a Check Engine light coming on.  Now that my Landrover is no longer in warranty, such occasional occurrences have grown from being a minor hassle to now being also an appreciable financial inconvenience.

My local Landrover dealership charges a minimum fee of $115 (plus waste fee, taxes, and who knows what else) just to decode the reason for the Check Engine light coming on and to reset it, before adding on whatever other charges apply for fixing the underlying issue (which as often as not seems to be a faulty sensor!).

It turned out the reason my Check Engine light was on was due to a high voltage level being detected at one of the sensors.  I remembered that I'd left the keys in the ignition (switched off, but just having the key in the ignition activates a bunch of standby circuits that slowly drain the battery) over a weekend and on the Monday morning, had a dead battery, and so had to recharge the battery.  When the engine first started after this, I had a high voltage event due to the charger and then the alternator going into panic maximum charge mode.  So this was a totally benign error, and I simply pushed the 'Clear Fault' button and the light obediently switched off and has stayed off ever since.

What a feeling of power that was!  I'd just saved myself something over $125, and I'd solved the problem, myself, in a matter of seconds, rather than having to take the vehicle in to the dealership for an entire day, make other transport arrangements for the day, etc etc.

I subsequently saved a friend a similar fee for their car which had a totally benign Check Engine light on too.

Fuel Economy improvements

I've learned some fascinating things since connecting the ScanGauge to my vehicle.

For example, when my car is idling, it uses 0.6 gallons of gas per hour if the transmission is in Drive, but only 0.46 gph if it is in Neutral.  Who'd have thought?  So, if I'm stopped at a light, I'll push the shift lever into Neutral.

Okay, so it would have to be many many hours of idling to save much money on this small saving.  But, I also learned another thing.  With gas at $2/gallon, and the vehicle using about half a gallon an hour, it is only costing me 1.5 for every minute the vehicle is idling.  So I'm no longer wondering/worrying if I should be turning off the engine every time I'm stopped and then restarting it a minute or two later.  The stress on the engine by stopping, letting it start to cool, then restarting it again, is not worth a saving of a couple of pennies.

Here's another fascinating thing I've learned.  If I'm coasting downhill and put the vehicle in Neutral, the engine burns about the 0.46 gph that it does when idling.  Okay - no surprise there.  But - get this :  If I leave the engine in gear, the engine switches off (many but not all modern engines will do this) and so it burns 0 gallons per hour of gas.  That's a new discovery for me, and not something I'd have guessed.  You'll get better fuel economy leaving your car in gear and your foot off the gas pedal than if you take it out of gear!

And, how about a third 'discovery' :  Almost always, without exception, keeping the car in a higher gear will massively reduce its fuel consumption.  I now will lock my car into top gear and leave it in top instead of allowing the auto transmission to shift between 4th, 5th and 6th gears during ordinary driving on the freeway at freeway speeds.  And when driving around town, I manually shift gears at lower revs, sooner than the auto transmission would do itself.  And, so as not to overstress the engine, I set one of the displays to tell me the engine loading - the percentage of maximum power the engine can develop that the engine is actually generating - once that starts to get above 90% I'll downshift, but until then, I keep the vehicle in as high a gear as possible.

So what does this all mean?  Well, you might think this number appalling, but I've got a heavy SUV, and I'm delighted to see that at present I'm averaging 20 mpg for the last 52.2 miles I've driven since last filling the tank.  This was for a mix of freeway and around town driving, and when you consider that the (usually ridiculously optimistic) EPA fuel economy figures for my 2006 Landrover LR3 are 14 mpg mixed and 18 highway; getting 20 mpg is beating the odds by somewhere between 15% and 25%.  That's a huge improvement in fuel economy, with only very small changes in my driving habits.

All the Different Information the ScanGauge can Show You

The unit has a small two line LCD display (you can change the color of the back lighting and adjust its brightness a whole bunch of different ways to suit whatever color scheme you wish), and on this display it can display four sets of data - one at each side of each line.

Real-time data

The unit comes pre-configured with probably twelve different 'gauges' you can select to display in each of the four different locations (I say 'probably' because not all vehicles report all twelve sets of data) and which give real-time information about what is happening under the hood.

By 'real-time' I mean instantaneous data, which changes and is updated every second or so (you can adjust the update rate if you wish), and this is different to average data values (see the next subsection below).

These twelve data values are :

  • Fuel Economy (ie mpg)

  • Fuel Rate (ie gph)

  • Battery Voltage

  • Coolant Temperature

  • Intake Air Temperature

  • Engine Speed (RPM)

  • Vehicle speed

  • Manifold Pressure

  • Engine Load (% of total power available)

  • Throttle Position

  • Ignition Timing

  • Open/Closed Loop (Oxygen sensor status)

You might have some of this data appear on instruments on your dash already (like mph and rpm), and some of the information is of little general interest to most of us, most of the time.  Currently, I have two of the four gauges set to tell me fuel economy and engine load, and I tend to play around with what I show on the other two gauges.  It has been interesting to see some of the gauges for a while during my researching the vehicle and how to get best economy from it, but now I no longer need to be looking at, eg, gph data all the time (which you can also calculate from mpg and mph data anyway, but only when the vehicle is moving).  It has been interesting to see the variation in ignition timing, and my next project will be to get a feeling for the impact of using different fuel grades on overall economy and performance, which will make this data again relevant (as well as horsepower and torque figures - see the next section).

Extra information from X-Gauge programming

In addition to these twelve data streams, you can program in extra data streams for potentially as many as 25 more items, depending on what items your car reports on.

This uses the unit's 'X-Gauge' capability, where you follow instructions to define additional gauges for things such as engine torque and horsepower, cylinder head and transmission fluid temperatures, oil temperature and pressure, barometric pressure, and, in the case of hybrid vehicles, various information about the state of the battery as well as the engine.

To add these extra data streams, you need to program in some settings to the unit.  This is not particularly hard, and you simply follow the step by step instructions provided by ScanGauge for what to program depending on the make and model of vehicle you have, and after doing so, you have now added the extra data monitoring.

Average values

In addition to the massive range of real-time data the unit can display, it also holds a series of averages for, eg, 'Current' (ie since the vehicle was last started), 'Today', 'Yesterday', and 'Since Last Fill'.  This is using the unit in its 'trip computer' type role.

It can display eleven different variables :

  • Maximum Speed

  • Average Speed

  • Maximum Coolant Temperature

  • Maximum RPM

  • Driving Time

  • Driving Distance

  • Fuel Used

  • Trip Fuel Economy

  • Distance to Empty

  • Time to Empty

  • Fuel to Empty

Some of these data points are fairly useless, and of course, don't base your refilling plans on when the trip computer says you're empty!

And some of the data points might be a bit embarrassing (I'm thinking of the maximum speed in particular).

The unit's implementation of 'today' and 'yesterday' values is massively flawed - it assumes there is a change of day when it is switched off for about eight hours - what it assumes to be an overnight.  It would be a very easy and inexpensive thing to add a true clock with local time to the unit (hey - this would be another thing to display - current time!), and then it would know exactly when days started and finished.  Maybe this will come out in a future version (this is, after all, the ScanGauge II, and we informally believe there will be a ScanGauge III one of these days).


You can set the unit to use liters or gallons, kilometers or miles, psi or kpa, and Celsius or Fahrenheit.  If you have a speedometer that isn't calibrated in both km/hr and mph, this might be useful if, eg, driving in Canada - you could set the ScanGauge to use km/hr and pull up a speed display.  Or, vice versa.  If your Canadian vehicle only shows km/hr and you're venturing south of the border, you can pull up an mph display as one of the four displays on the unit.

Using the ScanGauge with the Check Engine Light

This is really wonderful.  You'll get a great feeling of power - after all, 'knowledge is power' when you switch to this function.

Many of us have had the misperception that the Check Engine light is warning us of some imminent and grave disaster that is about to occur.

The reality is that most of the time, the Check Engine light is only reporting a fault in the vehicle's emission control system, and the problem it is advising may be either temporary or trivial.  Many cars have a different warning light (or, alas, no warning light at all) for major mechanical problems, and of course, with really serious problems, no warning light is needed - your vehicle simply stops working.

Do you really care if an oxygen sensor is faulty (problem code P0133)?  This may be something you need to get fixed before an emissions test (if your State requires one) but it isn't necessarily something that means you need to urgently rush into the dealership right away to get immediately fixed.  On the other hand, if you are told that you've a misfire on multiple cylinders (problem code P0300), that is probably something you should respond to sooner rather than later.

Now, with the ScanGauge, you can get it to tell you what the fault codes in the engine are which have caused the light to come on, and then, best of all, you can turn the light off again if you don't enjoy its little light shining at you on the dash all the time.

This gives you great peace of mind.  No longer is a Check Engine light a mysterious and worrying sign on your dashboard.

Note that the ScanGauge will just report a code - usually a letter and then a two, three or four digit number.  You'll then need to find out what the code means, and don't bother looking in your Owner's Manual, because you won't find it there.

Instead, go to a website like or or and look up the code there.  It will tell you what you want to know, and if you're still unsure, try calling the dealership and saying 'Oh, my --- is showing as ---, is that a problem or can it wait until I'm next bringing the vehicle in for servicing?'.  They'll probably want to encourage you in as soon as possible (they've got a living to make, after all) but a bit of careful questioning as to how exactly the car is being harmed by the fault condition should soon reassure you.

Using the ScanGauge in General

The unit is simple and easy to use, and displays its data reasonably clearly on the LCD screen.

Controls are intuitive, and the only problem you're likely to have is remembering what all the different gauge types are as you switch from one option to the next to the next.  For that reason, I keep the manual in the car with me.

Be careful not to become too distracted by the unit and the up to four constantly changing sets of data it can show simultaneously.  Mount the unit somewhere where you don't have to shift your focus too far from the road ahead to the unit, and remember the most important thing is to concentrate on driving, not on the ScanGauge.

Other Similar Products

There are plenty of other units that can be connected to your vehicle's OBDII port, ranging from 'test bench' type diagnostic and programming units to similar multipurpose consumer focused units similar to the ScanGauge.

None of the other units out there seem to be any better than the ScanGauge for general use, and all are appreciably more expensive.

You can also get software that runs on personal computers that will do the same type of thing as these dedicated devices if you just want to diagnose and reset your Check Engine light.  This software is usually considerably less expensive, but it is also considerably less convenient than the nice little self contained ScanGauge.


The ScanGauge II is a handy useful device that will help you drive more economically, gives you a wide range of additional information about the functioning of your vehicle, and can save you the sometimes unnecessary cost and worry when your Check Engine light comes on.

It has a list price of $169.95, and can be purchased at Amazon for $10 less.  We recommend also getting a second cable, which lists for $19.95 and is available on Amazon for $12.95.

If this sounds like the sort of thing you'd like, you almost certainly will like it, just as I do.  Recommended.

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Originally published 6 Feb 2009, last update 21 Jul 2020

You may freely reproduce or distribute this article for noncommercial purposes as long as you give credit to me as original writer.



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