[Biturbos4] Coolant sensor

Keman keman at interwolf.net
Mon Jan 5 21:46:18 EST 2004

These definitely go fairly often. It's a 4 wire sensor that can control both
the gauge and the ECM seperately. Your gauge in the instrument cluster may
read fine yet the ECM sees the engine as far out of range, or everything
runs fine yet the gauge in the cluster doesn't move or moves erratically.

The sensor is held in with a big nylon C clip, which sandwiches it against a
large O ring.

Once you've done one of these and know the orientation, all you have to do
is pop the overflow cap to make sure there is no pressure, put it back on to
keep coolant from coming out when you pull the sensor. Wiggle your hand back
there, yank the C clip with a long flathead screwdriver such that the clip
pushes into your very wedged (but ready) fingers, pull the sensor out with
the harness still attached to it (makes a great handle to grab by),
disconnect harness, put new sensor and -new o ring- in old spot, slide
c-clip in place, reconnect harness and poof. Maybe 5 minutes.

This is definitely something a do-it-yourselfer can tackle, just try not to
drop anything behind the engine else you get to go fishing. Do it on a cold
engine, and it's the sensor that's on the passenger side rear of the engine.
Release the fuel lines from the triple clip that holds them in place back
there to push them out of the way for more access.

Btw- this is just my opinion on how to do it, there may be better ways...
whatever you guys do don't take me as thinking my opinion is superior just
cuz I work at the dealership. Far be it from me to lay down some "final word
as the audi god". In fact most of the tricks I know I've learned by watching
others and I'm always looking for some new ways to do stuff-- so post em! :)

- Keman

> I got a CEL last friday night when it was -25 oC outside, it stayed
> on all Saturday but cleared itself yesterday.  I figured I'd be safe
> and drop by the dealer at lunch today.  I was expecting a MAF or a
> torn TBB, but it tuned out to be a coolant sensor, it's out of spec
> by up to 10 oC.
> I did a quick search on the AW S4 archive, apparently this sensor is
> known to fail, quite frequently I might add.  It can cause rich or
> lean conditions, cold start and idle problems, erractic coolant temp
> gauge and other issues.  Also the original sensor (black) has been
> superceded by a newer version (green).   I learn something new
> everyday, just thought I'd share my findings.
> Btw, happy new year!!
> Quincy
> '01.5 S4
> '90 CQ
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> Biturbos4 at www.audifans.com
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