Re: coolant temp sensor

[Phil Rose <pjrose@servtech.com>]

>-----Original Message-----
>From: Phil Rose <pjrose@servtech.com>
>To: quattro@coimbra.ans.net <quattro@coimbra.ans.net>
>Date: Wednesday, June 17, 1998 2:30 PM
>Subject: coolant temp sensor
>
>
>>The ACC diagnostic channel 01 ('89 100) has always produced an 09 code,
>>which I have ignored until recently. According to the Bentley, the 09 code
>>means a faulty "engine coolant sensor"--the one that's inserted just upside
>>the large coolant hose/thermostat flange. I ran the electrical tests and
>>everything appears as per specs--both the sensor resistances and the
>>voltages at the connector pins. So...why does the ACC tell me there's a
>>problem here?
>>
>>According to the manual, the symptom of a defective coolant sensor will be
>>hard cold-starts and rough running during warmup. I've never noted the
>>former, but the latter symptom is sometimes present in winter. Is it
>>possible that the 09 code from ACC channel 1 of '89s is not meaningful?
>>
>>Phil
>>
>>Phil Rose Rochester, NY
>
>
>
>Hi Phil;
>
>    You may have a bad connection which the A/C control head interprets as a
>defective coolant sensor. I just had a problem with the A/C head setting 07
>and 15 trouble codes - defective temperature control flap motor and/or
>feedback potentiometer. Also had physical evidence of a problem - the unit
>wouldn't maintain temperature. I followed the Bentley troubleshooting
>procedure and it identified the temp flap motor as defective. Hmmm, that
>motor looks awful expensive. Put the magical Stabilant 22A on the A/C head
>connector pins and the temp flap motor connector - problem solved! It now
>works like a charm and no more trouble codes.
>
>HTH
>
>Fred Munro
>'91 200q  254k km

Fred,
I've measured the voltages at the connector contacts (vs ground) with the
ignition switched ON and get 4.5 to 5.0 volts at both--as per Bentley. So I
think that tells me the connection back to the AC controller is OK. As far
as the continuity between connector and the sensor is concerned--that
_might_ be bad, but doesn't look at all suspicious. I guess I could attach
a couple of jumper wires to check that out.

Or (it just ocurred to me), one thing to try is to insert a 1k ohm resistor
across the connector contacts and see if the diagnostic code changes at
all. If it doesn't, that would clearly show the 09 code is an A/C head
problem (or characteristic).


Phil

Phil Rose		Rochester, NY
'89 100
'91 200q		pjrose@servtech.com