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 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
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
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
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 temperature derived from an engine
coolant temperature sensor or a cylinder head temperature sensor.
- displays the current engine revolutions per minute
- Fuel Rail Pressure (gauge)
- displays the fuel rail pressure at the
engine when the reading is referenced to atmosphere (gauge
- ignition timing advance for #1 cylinder (not
including mechanical advance).
- 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
- 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
- increments the time since the engine was
started while the engine is running.
- 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,
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.
- displays the ambient air
- Barometric Pressure - barometric pressure normally obtained from a
dedicated barometric sensor.
- Catalyst Temp (up to 4) - displays the catalyst substrate
- 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%
- 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
- 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
- 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
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
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.
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.
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
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.)
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
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.