[V8] Short to (+) Intake Air Temp Sensor

dsaad at icehouse.net dsaad at icehouse.net
Thu Jun 23 10:07:42 EDT 2005


When trouble shooting a computer based system (which is what the ECU is), it
helps to think like a computer.

First off, the IAT sensor is resistive. This means it is very easy to test at
home with only a simple ohm meter. The "transfer function" or table of
resistance to temperature is somewhere in the manual. The ECU measures this
resistance by forcing a known current through the IAT and measuring the voltage.
If the voltage is 0 or close to it you get the shorted to ground error code. If
the voltage is too high you get the shorted to positive message. Since one IAT
terminal is usually connected to ground, if either terminal is open, or the
sensor is open, the current force circuit goes to maximum voltage in a futile
effort to produce current in an open circuit (by definition an open circuit is 0
current) - hence the "short to positive" error code.

So - to test the sensor on the car, you would need to measure the voltage right
across the IAT terminals. Some possible readings:

5v - would indicate the wire connections are good, but the sensor is open. (bad
sensor)

somewhere in the range of about 1 to 4 volts - would indicate the system is
working. Now you need to find how to convert this voltage to a temperature to
see if it is correct.

0 to 1 volt would indicate the sensor has somehow shorted (perhaps it is
contaminated with something - clean it off) or the ECU current forcing circuit
is bad (probably means a new ECU but this is not likely) or there is high
resistance in the wiring to the sensor.

Dave



Quoting "Miller, Chris" <chris.miller at infofoundry.com>:

> If you read codes with the 1551 or an emulator, you'd get the 00523
> rapid data code; corresponds to a 2322 "blink" code.
> G42 Intake Air Temperature (IAT) sensor.  It can differentiate between
> signal to negative or signal to positive.
> Condition:
> short circuit to ground
> open circuit between IAT and terminal 44 of ECM
> IAT malfunctioning
> ECM malfunction
>
> I'm not near the V8 tonight; is the sensor something you can swap out,
> or is it like the turbo cars (welded to harness)?  Anyone got a good
> used spare for troubleshooting?  Also check the continuity of the wire
> to terminal 44 of the ECM; then see if you can find somewhere that the
> harness could be damaged.
>
> Any other codes??
>
> Chris
>
> -----Original Message-----
> From: v8-bounces at audifans.com [mailto:v8-bounces at audifans.com] On Behalf
> Of Andy Schor
> Sent: Wednesday, June 22, 2005 5:01 PM
> To: v8 at audifans.com
> Subject: [V8] Short to (+) Intake Air Temp Sensor
>
> Greetings Gents,
>
> If you remember the "no, Officer" thread, I have been having an
> intermittent condition of surging (revving) at idle along with (but not
> at the same time) a situation where the CEL is lit and the car runs
> rough (with an abrupt on/off throttle).  The code reader says, "00523
> Short to Positive, Intake Air Temperature Sensor".  This has been
> replaced as well as ISV, O2 sensor, knock sensor and associated
> connectors.  The condition will become evident immediately upon
> starting, usually when warm (but not always).  I have noticed that when
> it is in the CEL mode (limp home?) the idle doesn't surge.
> Most of the time the car drives fine, the condition comes and goes
> although it seems more likely on a warm restart.  Of course yesterday
> after a few good stop and starts, I got the CEL mode for the ride home.
> I parked in front of the house, turned it off and back on (which I had
> tried earlier) and it fired up with no CEL.
>
> I have tried (with limited success) checking the connectors in the front
> for the offending sensor(s), but they get kind of hot and I didn't want
> to burn my fingers (again).
>
> All thought and suggestions appreciated,
>
> Andy Schor
> '91 V8QM
> '91 Avant
> (Either or both soon to be for sale)
>
>
>
> --
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