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Reading Your Car's Brain - Part 2

Using the Auterra OBD scan tool.

by Julian Edgar

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Last week we covered the basics of accessing the OBDII data stream available in nearly all recent cars. To briefly recapitulate: there are four different OBD data stream formats that may be available from the specifically-shaped OBDII connector. The pin placement in the connector will vary, depending on the data format used, while extra pins may be used for manufacturer-specific functions. To read the OBDII data stream, you'll need to have a car that is actually OBDII compliant, and have a reader (comprising both software and hardware) that will allow you interpret the particular format being used. (For more detail on all this, go to "Reading Your Car's Brain - Part 1".)

That's the theory - what about the practice? In this story we'll review the Auterra Dyno-Scan tool which is used in conjunction with a Palm (or Palm OS-based PDA or smartphone). In addition to being able to display generic OBDII data and read and cancel fault codes, the device can also be used as an on-road dyno - which we'll cover in detail later.

The Box

The Auterra DynoScan tool costs from US$289. While there are cheaper OBDII scanning packages around, we chose Auterra because of its on-road dyno capabilities, the company's excellent response time to emailed questions, the wide range of compatible PDAs, the fact that the system can read all four OBDII protocols, and the extensive documentation that is available for online download.

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In the box you'll fine a hot-sync cable (specific to the Palm handheld being used), the OBDII hardware adaptor (only a little bigger than a couple of matchboxes), an OBDII cable that connects the adaptor to the car's OBD port, and a software CD which also contains the manuals.

The first step is to install the software onto the PC, and from there onto the Palm. This is easily achieved by hot-syncing - ie, the same process followed when backing-up Palm data or loading any other software onto a Palm. From there it's just a case of plugging the OBD cable into the adaptor and the car's OBD socket, and connecting the Palm to the adaptor via the supplied hot-sync cable.

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Note that the OBDII socket might not be immediately accessible. In the 2003 Holden Astra shown here, it is normally hidden under a trim panel beneath the handbrake lever. A small screwdriver is needed to lift the trim panel out - it's clipped into place.

Communicating with the Car

The opening screen display is shown here. There are three options: connect to vehicle, enter the software program but don't connect (useful if you want to change some options without actually displaying live data), and a demo option (which can be accessed without the Palm being connected to a car or even to the OBD adaptor.) The latter mode is a good way of getting familiar with the software, which can be downloaded free from Auterra.

Tapping the 'Connect to Vehicle' option starts the connection process; if it is successful a 'General Info' display will appear. If the Palm cannot connect to the ECU, various error messages will appear, depending on what the problem is.

However, these messages aren't very specific - Auterra has a better way of sorting out the problem and that is to record a Communications Log file and then email it directly to the company. From the log file they can determine the exact cause of the problem - for example, the adaptor not receiving power from the OBD port, or the ECU lacking internal OBDII software functionality.

The General Info includes information such as the OBD requirement to which the vehicle was designed, the presence or otherwise of ECU software such as a misfire monitor, and the status (eg open loop or closed loop) of the fuel system. As the name suggests, it's just a general information screen.

Displaying Live Data

But much more interesting to us is the ability to display live data. There are a number of ways of doing this and one of the best is the Meter Screen. In this mode the Palm displays - in large and clear numbers - any two selected parameters. In the example shown here, the two are engine rpm and oxygen sensor volts, but the selected parameters can be any supported by the car's OBDII port. So what are they, then? (The following listing is reproduced from the Auterra handbook.)

All OBDII cars will have available:

  • Air Flow Rate From MAF - indicates the airflow rate as measured by the mass air flow sensor.
  • Absolute Throttle Position - the absolute throttle position (not the relative or learned) throttle position.
  • Calculated Load Value - indicates a percentage of peak available torque. Reaches 100% at wide open throttle at any altitude or RPM for both naturally aspirated and boosted engines.
  • Engine Coolant Temp - engine coolant temperature derived from an engine coolant temperature sensor or a cylinder head temperature sensor.
  • Engine RPM - displays the current engine revolutions per minute value.
  • Fuel Rail Pressure (gauge) - displays the fuel rail pressure at the engine when the reading is referenced to atmosphere (gauge pressure).
  • Ignition Timing Advance - ignition timing advance for #1 cylinder (not including mechanical advance).
  • Intake Manifold Pressure - indicates the manifold pressure derived from a Manifold Absolute Pressure sensor.
  • Long Term Fuel Trim (up to 2) - indicates the correction being used by the fuel control system in both open and closed loop modes of operation.
  • O2 Sensor (up to 8) - indicates the voltage for conventional 0 to 1V oxygen sensors. O2 sensors with a different full-scale voltage are normalized to this range or, if a wide range sensor, may instead use the wide range parameters (see below).
  • Short Term Fuel Trim (up to 2) - indicates the correction being used by the closed loop fuel algorithm. If the fuel system is open loop, 0% correction is reported.
  • Time Since Engine Start - increments the time since the engine was started while the engine is running.
  • Vehicle Speed - displays the vehicle road speed.

When you look at these parameters you can start to get an inkling of how useful the data is when modifying cars. For example, the mass airflow meter readout is in grams/second - now for the first time ever, you can actually work out exactly how many cfm of air are being breathed by the engine at full load, peak power!

The ignition timing advance can be used to indirectly indicate knock sensor ignition timing retard - if the timing suddenly retards at full load, it's because the knock sensor is telling the ECU that detonation is occurring.

The ability to see the Short and Long term Fuel Trims allows you to watch the learning behaviour of the ECU - perfect if you've fitted a big exhaust and are wondering how the ECU is coping. You can take the information even further - if the peak mass airflow increases after a modification, it's nearly certain that the power has also gone up.

As you can see, even with these basic parameters - supported by all OBDII cars - there is a wealth of useful information available. But it doesn't stop there. Many cars also support some of the following parameters:

  • Absolute Load Value - is the normalized value of air mass per intake stroke displayed as a percent.
  • Absolute Throttle Position (up to 3) - the absolute throttle position (not the relative or learned) throttle position.
  • Accelerator Pedal Position (up to 3) - the absolute pedal position (not the relative or learned) pedal position.
  • Ambient Air Temperature - displays the ambient air temperature.
  • Barometric Pressure - barometric pressure normally obtained from a dedicated barometric sensor.
  • Catalyst Temp (up to 4) - displays the catalyst substrate temperature.
  • Commanded EGR - display 0% when the EGR is commanded off, 100% when the EGR system is commanded on, and if the EGR is duty cycled, somewhere between 0% and 100%.
  • Commanded Equivalence Ratio - fuel systems that use conventional oxygen sensor displays the commanded open loop equivalence ratio while the system is in open loop. Should report 100% when in closed loop fuel. To obtain the actual air/fuel ratio being commanded, multiply the stoichiometric A/F ratio by the equivalence ratio. For example, gasoline, stoichiometric is 14.64:1 ratio. If the fuel control system was command an equivalence ratio of 0.95, the commanded A/F ratio to the engine would be 14.64 * 0.95 = 13.9 A/F.
  • Commanded Evaporative Purge - displays 0% when no purge is commanded and 100% at the maximum commanded purge position/flow.
  • Commanded Throttle Actuator - displays 0% when the throttle is commanded closed and 100% when the throttle commanded open.
  • Control Module Voltage - power input to the control module. Normally the battery voltage, less any voltage drop between the battery and the control module.
  • Fuel Level Input - indicates the nominal fuel tank liquid fill capacity as a percent of maximum.
  • Fuel Rail Pressure - indicates the fuel rail pressure at the engine referenced to atmosphere (gauge pressure).
  • Fuel Rail Pressure Rel Manifold - displays the fuel rail pressure referenced to the manifold vacuum (relative pressure).
  • Intake Air Temperature - displays the intake manifold air temperature.
  • O2 Sensor Wide Range mA (up to 8) - shows milliamps for linear or wide-ratio oxygen sensors.
  • O2 Sensor Wide Range V (up to 8) - shows voltage for linear or wide-ratio oxygen sensors.
  • Relative Throttle Position - relative or "learned" throttle position.

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While some of these parameters aren't all that useful, others are vital info when modifying a car. For example, the cat converter substrate temp will give a very good indication of whether the cat will live at the higher loads of a modified car, the intake air temp on turbo cars will show how effectively the intercooler is working, while the display of data from factory wide-range oxygen sensors is likely to give an excellent indication of air/fuel ratio.

In the Meter display mode, the readout (here being displayed on a Handspring Treo 270 smartphone) is large and clear, easily able to be read even from across the cabin. However, in many situations - especially when working alone - the continuous reading of the Palm will be difficult. In that case two options are available: the data can be displayed on a moving line graph, and/or it can be logged.

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As in Meter mode, any parameter can be selected for graphing and it can be displayed either alone or in conjunction with another parameter. In this case, the output signal of two oxygen sensors is being displayed - Sensors 2 and 3 in Cylinder Bank 1. Clearly Sensor 3's behaviour is different to Sensor 2 over the second part of the graph - perhaps indicative of a sick sensor of changed mixtures in one bank of cylinders.

In the Astra Turbo, we logged a line-graph of throttle position against intake air temp (measured after the intercooler) and did some high load test runs. The gear changes were easily able to be seen in the throttle position trace, while the intake air temp could be read off the graph as it rose with load. In this case it was easy to see that the intercooler on the Astra Turbo is likely to be marginal in hot weather - we saw temps around 60 degrees C in 20 degree C ambient conditions. A marker can be placed on the graph so that the data can be read off in numerical form at any selected point. This data can also be exported to a PC spreadsheet.

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Live data can also be displayed in a multiple meter mode. The numbers aren't so large, but the ability to show five different parameters on the screen simultaneously can be very useful in some situations. For example, here Throttle Position, Intake Air Temp, Long Term Fuel Trim, Engine Coolant Temp and Engine RPM are being simultaneously displayed.

Other Functions

The Auterra Dyno-Scan also has the ability to read stored and pending fault codes, display in English what the codes mean, and clear them as necessary. In ECUs that support the function, a 'freeze frame' showing all the engine operating parameters at the time that the fault occurred can also be displayed.

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In some cars an analysis of the health of the oxygen sensor(s) can be carried out, including maximum and minimum voltage outputs, switching times between rich and lean conditions, and the sensor swing period.

The sampling speed of sensors can be configured and units can be displayed in either English or Metric (although the transformation isn't seamless: some units stay in English.)


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If you are modifying a recent car that is fitted with an OBDII port, an OBD reader is almost a must-have. The sheer amount of information that can be displayed makes it far more likely that intelligent modification decisions can be implemented, and modifications that are made can be much better assessed for how they're working with the standard ECU.

The Auterra DynoScan tool is easy to use. Because of its Palm interface it can't display data quite as clearly as those scanners using a laptop PC - but of course the Palm can be easily mounted on the dash in a way that would be very difficult with a laptop! The logging and display functions work very well and the software/hardware combination is versatile and effective.

Next: trialling the on-road dyno function of the Auterra DynoScan

The Auterra DynoScan tool was purchased for this review

Buying Long Distance

Something to be aware of if buying the Auterra DynoScan tool from outside of the US is that additional costs quickly add up.

By the time the costs of a Western Union money transfer (Auterra doesn't accept credit cards for international orders), air freight with UPS, and Australian customs inspection and GST were all paid for, about AUD$200 needed to be added to the original purchase price to land the device in Australia.


If your car uses an interceptor to modify the fuel or ignition timing, the OBDII reader will display incorrect information for these two parameters. This is because an interceptor works by changing the signals going to (or coming from) the ECU - and the ECU doesn't know anything about it. For example, if the fuel mixtures are altered by reducing the output signal of the ECU, the OBD data will show a lower mass airflow than is actually occurring.

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