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

Thu Jun 23 11:52:48 EDT 2005

Dave, Chris and everyone else,

Thanks for your response(s).  I don't have a manual or schematic for the V8 
(although I have them for the 200q20v), but I do have access to Alldata.  I 
have printed your message and will go over it with my mechanic.  It is 
possible that the replacement sensor is bad, but I think it may be the 
wiring.  When the car is running well (most of the time) it runs great.  As 
soon as I turn the key on I'll know, either all's well or the CEL is lit. 
This is true under both conditions.  If the CEL is on and I turn the car off 
and let it sit for a while, it usually (but not always) starts fine.  If it 
is running well and I shut it off, then restart (like going shopping or 
buying gas), it may/may not be in CEL mode.  Concurrently it still has the 
surging idle (but not in CEL mode), I don't know if the two are related or 
coincidental.  Maybe I'm not explaining it well.  What else should I be 
considering?

Andy

----- Original Message ----- 
From: <dsaad at icehouse.net>
To: <v8 at audifans.com>
Sent: Thursday, June 23, 2005 9:43 AM
Subject: RE: [V8] Short to (+) Intake Air Temp Sensor

> 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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>
>
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