diagnosing IAC PCM signal
05-06-2015, 10:56 AM
#1
diagnosing IAC PCM signal Hi guys,
Having some trouble with the IAC and I want to check if the IAC and/or the PCM are actually working to control it. My understanding is that I should test the IAC harness wires against ground to check for voltage. I have read that this must be 'real voltage' and not some small noise voltage. Does anyone have any more info on this? What voltages should I see? Should the car be running? Any other insight?
If this electrical check seems OK, how can I test the IAC itself? I have the torque app and can scan the data. Do I also need another scan tool to command IAC steps? Is this able to be rented? What do I look for?
thanks
Joe
Having some trouble with the IAC and I want to check if the IAC and/or the PCM are actually working to control it. My understanding is that I should test the IAC harness wires against ground to check for voltage. I have read that this must be 'real voltage' and not some small noise voltage. Does anyone have any more info on this? What voltages should I see? Should the car be running? Any other insight?
If this electrical check seems OK, how can I test the IAC itself? I have the torque app and can scan the data. Do I also need another scan tool to command IAC steps? Is this able to be rented? What do I look for?
thanks
Joe
05-06-2015, 12:03 PM
#2
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Tuning packages like HPTuners and EFILive, their scan
tools have "bidirectional controls" which can push the
IAC, and if RPM moves you've got a working one.
IAC signals are two coil-driver signal pairs which do
not have a lot of activity and don't look like much on
a meter. But you can distinguish a PCM that has, and
one that omits the IAC driver circuitry by the degree
of "noise" voltage on the driver pins; should see on
a DMM, flickering hundreds-of-mV if drivers are present,
and tens of mV or less if they're blank pins.
tools have "bidirectional controls" which can push the
IAC, and if RPM moves you've got a working one.
IAC signals are two coil-driver signal pairs which do
not have a lot of activity and don't look like much on
a meter. But you can distinguish a PCM that has, and
one that omits the IAC driver circuitry by the degree
of "noise" voltage on the driver pins; should see on
a DMM, flickering hundreds-of-mV if drivers are present,
and tens of mV or less if they're blank pins.
05-06-2015, 12:53 PM
#3
Thanks for your reply Jimmy. Can you specify more about testing the PCM circuitry? Which pins should I test against ground? All of them? Should the car be running and idling? Cold or hot? Or doesn't it matter?
Do any handheld scan tools have the ability to control the IAC? Like ones you can rent from an auto parts store.
thanks
Joe
Do any handheld scan tools have the ability to control the IAC? Like ones you can rent from an auto parts store.
thanks
Joe
05-06-2015, 09:19 PM
#6
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Well, it certainly means it has live driver circuitry. But
it seems like it's pinned to a single state instead of
thrashing around (normal behavior, trying to hold an
airflow value by dithering the IAC plunger position).
Maybe KOEO does not try to move the IAC. At any rate
the voltages are sane for a single fixed position. If you
have it running, you should see "noise" (moving too fast
for the meter) instead. I use sewing needles soldered
to a spare set of leads to probe through insulation.
it seems like it's pinned to a single state instead of
thrashing around (normal behavior, trying to hold an
airflow value by dithering the IAC plunger position).
Maybe KOEO does not try to move the IAC. At any rate
the voltages are sane for a single fixed position. If you
have it running, you should see "noise" (moving too fast
for the meter) instead. I use sewing needles soldered
to a spare set of leads to probe through insulation.