I'm getting an engine temp light fault light a few minutes after driving the car (1987 S 4). gage shows normal temp, and I've never had a problem with overheating. Fluid is fine. and it comes on way too soon for water temp even to get to 180; sometimes it goes off for alittle but always comes back on. So I'm thinking it's an electrical gremlin?
where should I start troubleshooting?

also probably unreleated but horn is inoperative also, in case it's on the same relay as the engine temp light.

 

what year is your car

 

1987 S4

 

have you ever replaced any of the connectors on the water bridge?
has the water bridge ever been removed for maybe an intake refresh?
How many miles on the engine? has it recently gotten wet?
If the temp sensor is original and also the connector its possible that the wires are damaged so adding a new connector is a start,
if the sealing ring is corroded or the water bridge was powder coated then the ground may not be good.
easiest thing to do is pull the connector and put some deoxit 100 into the connector,
also add some to the sealing ring of the sender.

if the wires are damaged on the temp sensor its also wise to replace the temp 2 sensor connector,

so things to do
replace both connectors on the water bridge if the part was PCd then clean the WB screws seating area.
clean the sealing rings of each sensor
if either sensor looks like its corroded it might be time to replace the sensors the S4 temp sensor is expensive

 

good call. it happened after the intake was removed to fix something deep in the engine, or maybe it was the timing belt. but the manifolds were definitely off the car.
water bridge? is there a written procedure for checking ?

 

i think i just wrote it read post 4

 

Had this issue on an 86.5 a couple months back. Ended up being the two nut connection on the back of the instrument cluster was corroded just enough to give a bad signal. Cleaned those up and the issue went bye bye.

 

yikes, you have to remove the instrument panel to fix it?

 

No. If it's the gauge cluster, you have to remove the POD to fix it. Pulling the pod in a non-airbag car is a pretty simple task. Dwayne has a very good writeup on it. I've done it a few times and I can have mine out in 15 minutes or less, back in in about 20.

And it may well be the sensor or the connections to the sensor, or the water bridge issue; the stuff Stan covers in post #8.

 

the connector on the driver's side seemed alittle corroded at the connectors, so i removed both, wire brushed the crud off from the base prongs and wired connectors, sprayed some electrical connector cleaner and reattached.
Will wait awhile for it to dry and then do a test run.