Coolant temp sensor testing?

Hi everyone,
My car is golf 3 tdi 1996.
I'm experiencing a possible failure of the coolant temp sensor; a sudden unintended acceleration at firing the engine when it's hot. With the the coolant temp plug unplugged the car starts normal and doesn't accelerate by itself. So before attempting to replace the sensor, I want to go through the wiring check and the sensor itself.
Could you plz guide me on how to check the wiring and the sensor?
Thanks

Take the stop solenoid out of the top of the pump and check the o-ring. Make sure it has not gotten out of its seat, or that it is deformed or damaged in any way. If so, replace it.

The Bosch part number for the o-ring is: 1 460 210 006

oilhammer said:

Take the stop solenoid out of the top of the pump and check the o-ring. Make sure it has not gotten out of its seat, or that it is deformed or damaged in any way. If so, replace it.
The Bosch part number for the o-ring is: 1 460 210 006

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Everything is secured in place. My concern is to check the wires for being shorten or the sensor lost an amount of resistance.

Westwindmk3 said:

Everything is secured in place. My concern is to check the wires for being shorten or the sensor lost an amount of resistance.

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the sensor is what makes the resistance, not the wire. The sensor has a small wire in it that has a known constant resistance at specific values of temperature. nothing to do with the wire leading to it.

Mongler98 said:

the sensor is what makes the resistance, not the wire. The sensor has a small wire in it that has a known constant resistance at specific values of temperature. nothing to do with the wire leading to it.

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Do you have an idea about the value of resistance through the increase of temperature, and how to measure resistance, which pins to measure?

I don't believe VW has published the temperature/resistance curve for the MKIII CTS... which, along with a calibrated water bath, is what you'd need to do this job. Just checked my Bentley and there's no calibration chart there.

It also sounds like it's intermittent, so might even pass the test on the bench.

Given that the sensor is less than 20 bucks IIRC and a frequent fail item, particularly on older models, you might want to consider just replacing it, depending on what you think your time is worth.

I'd also echo Oilhammer's suggestion: the symptoms you describe are exactly those related to a failing o-ring on the injection pump's stop solenoid... unless there's a prefect correlation with the failure only happening when the CTS is plugged in...ie you can restore the system to normal in real time by unplugging the CTS.

Me I'd be ordering a new CTS plus a 25 cent o-ring and cover my bases.

Maybe this will help you:-


https://i.imgur.com/tCxDRY2.jpg

Perfect! And it looks official! Where did you track it down?

It's from Autodata

CasaEd said:

Maybe this will help you:-


https://i.imgur.com/tCxDRY2.jpg

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NICE FIND
that's exactly what OP needs. Bookmarked.

CasaEd said:

Maybe this will help you:-


https://i.imgur.com/tCxDRY2.jpg

Click to expand...

Copied that photo, thank you for posting!!

Steve

Commenting to also find this info later.
Engine coolant temperature sensor resistance curve diagnostics
https://i.imgur.com/tCxDRY2.jpg

CasaEd said:

Maybe this will help you:-


https://i.imgur.com/tCxDRY2.jpg

Click to expand...

Thanks a lot