G62 (coolant temp sensor) problem/UPDATE

Phil Rose pjrose at frontiernet.net
Mon Jun 17 22:45:51 EDT 2002

When is a G62 sensor _not_ a G62 sensor?

Well, Bentley labels the engine coolant temp sensor--the one located
in the rear of the block on the right (pass. side)--as "G62". This
sensor is (supposed to be) connected to the ECU. Whether or not that
connection is good (and how the ECU uses the sensor output) is still
unknown to me. However I've have discovered that the problem causing
CC diagnostic codes in ch 1 (code 09) and ch 6 (code 255) are
actually related to a _different_ engine coolant
sensor--specifically, the one that's built in to the heater control
valve assembly. In the climate control section of the Bentley manual,
this one is also--confusingly-- refered to as "G62", but in fact the
wiring diagram simply calls it "coolant temperature sensor".  It
reports just to the A/C controller. Both of the coolant sensors may
be identical, electrically, but they have different functions.

So, why the CC errors? Evidently the wires had been given a good hard
tug by some previous monkey lad. Consequently, inside the rubber boot
of the connector I found both wire connections had been pulled
completely out of their holder (a pink plastic insert), and this
holder had also been broken out of the external (white plastic)
housing. So although the sensor's connector appeared to be
"attached", there was no electrical contact being made. I was able to
rebuild/reassemble the connector (Bernie would be proud), and now CC
channel #1 reorts "00", and channel #6 reads correctly. I'm not aware
of what improvement this will make in the car's climate control
operation--perhaps it has to do with the warmup period before the
heater blower is allowed to operate.

I realize this will have absolutely no effect on the starting problem
(probably fuel pressure related).


At 6:53 PM -0400 6/16/02, Phil Rose wrote:
>With our newest Audi (tornado), the engine starts quickly when cold
>but it becomes progressively harder to start as it warms. It can very
>difficult to restart if it's been warmed up and then sits for about
>1-2 hrs before a restart. At first I assumed some sort of
>injector/fuel-pressure issue, but today I  found another lead;
>however I'm not certain if it is relevant to this problem:
>(1) I've found that the CC diagnostic channel 6 reads  a constant
>"255" (regardless of engine temp), which means an open circuit for
>the G62 (coolant temp) sensor. However,
>(2) The G62 sensor output (disconnected) is OK--its resistance has an
>expected low value (about 350 ohms, meaning high temp) when the
>engine is hot, and it then increases to the expected 2800 ohms (+/-)
>after the car cools off in garage overnight (65F). The sensor itself
>thus seems OK.
>So it appears there is a wiring problem--or possibly a need to
>replace the CC head unit. But will fixing this G62 issue  improve the
>hot starting? I reckon that the ECU needs to know engine temp in
>order to to adjust the fuel/air for starting. Does it get this info
>from G62? If so, then our defective circuit can mislead the ECU into
>"thinking" the coolant is very cold all the time. On most "cold"
>starts this is tolerable, but after warmup, the restarts would be be
>using a mixture that is too rich. (????) Anyone encounter a G62
>problem of this sort? Am I on the right track?

Phil Rose				Rochester, NY USA
'91 200q	(130 Kmiles, Lago blue)
'91 200q   (57 Kmiles, Tornado red)
	mailto:pjrose at frontiernet.net

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