Big, Big Time Poster
Coolant Temp Sensor
Can someone describe what happens when your coolant temp sensor doesn't work? 1990 535im. Which one is it, where is it located? How does it affect things at upper RPM? I seem to have a rev limiter condition at acceleration and wonder if I need a CTS. I have to pull the cap and check it and the rotor also. It's finally warm enough to keep from getting numb fingers. My mileage has slipped from 20 on the road with more acceleration to 15 and bogging. Conforti chip present. Thanks.
4 Grand Master
The voltage output decreases or becomes erratic or zero causing the ECU to 'think' the engien is at a different temp. Will cause all kinds of trouble. Get a voltage meter on them to test- the specs are in the Bently nad the sensors on the water neck. There is one in the AFM also, but it is more reliable.Originally Posted by ahlem
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08/88 535i e34 M30+miller MAF, 'stiens, tints & teeth!
Big, Big Time Poster
If the coolant temp sensor (CTS) is broken then the ECU might think that the engine is cold - if the ECU thinks that the engine is cold then (even if the engine is warm) the ECU will put the "choke" on - i.e. it will inject extra fuel. Might be what is knackering your mpg...
Big, Big Time Poster
Sounds like I'm heading in the right direction. I don't have a Bentley Manual, only the sketchy Haynes. There are two sensors on the water neck. Which one would cause the most problem. Anyone have a link to the specs or testing procedure? Thanks.
3 Grand Master
one is the temp sensor for your gauge the other for the ecu.one is brown,one is blue. i dont know which is which!
Gone but not forgotten
Major Contributor
Doesn't really matter which one is which. You can check the sensor by switching the temp sensors and watch if guage displays correctly. More often the contacts could be corroded in which case the problem would "fix" itself after you perform the switch.
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3 Grand Master
true...i once had a dodgy temp gauge which after i removed the terminal checked wire es et,and reconnect worked fine
Super Moderator
2 Grand Master
Curious:
Why would we need two separate sensors with two different parts #s if they perform the same job? Why not send the message from one sensor to both the guage and the DME?
In trying to track down an engine stumble, I swapped the engine temp sensor and coolant temp sensor wiring (new sensors as well). The temp guage needle sat at the 1/4 mark at operating temp when connected to the engine temp sensor. Do I indeed have a bum engine temp sensor???
Dave M
10/90 Build 525im, 630,000+km, Eibach/Sachs, Engine Rebuild
*RIP Oskar the DOG*
Major Contributor
Not sure, when I did my HG job. I think I accidentally swapped them and it still worked the same. You can't really share sensors. So you would need to send one signal to DME and then DME would send it to Guage, I guess historically it came that way, don't know.
The sensor is just a resistor which I can't see how it can go bad. But anything is possible I guess? Try to clean up contacts to see if it helps.
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