ECT Sensor & Fans problem

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Joined: Sun Dec 24, 2017 8:34 pm
Drives: 2004 Twist 1.2L Petrol 3 Cylinder (9N)
Location: Manchester, GB

ECT Sensor & Fans problem

Post by shaunmcbride » Sun Dec 24, 2017 9:02 pm

Hi all!
First post to the forum and new to fixing my own car in general so please be patient with me haha!

First a bit of history (the documentation of which might help other people if they have the same problem and search for a solution), then Id like to ask my current problem.
My 2004 Polo 1.2 Petrol recently began with an intermittent starting issue, always after the car had already been used that day (warm)

#1: Cranked but not firing first time, started fine second time
#2: Cranked but not firing first time, started second time with accelerator boot but stalled as soon as foot taken off accelerator. Started third time fine.

-- changed fuel filter in case that was the problem - -

#3 Cranked but not started a few times. When finally started, engine okay in idle but stalled when pulling away. Eventually worked fine.
#4 Again cranked no starting. Worked after 30mins cooling.

Also noticed that my oil temp gauge could be quite erratic. Somes it goes up to 90c sometimes when pressing accelerator and dropping to 0c when taking foot off. Sometimes the needle is stuck to 0 for a long time. Sometimes it goes up super fast. On reading my OBD, sometimes my ECT thought it was - 20c one minute then 75c the next.

Having read forums and spoken to mechanics, it appeared the ECT sensor is a common fault on the car, and it produces symptoms similar to those Ive had by running the fuel too lean. I bought a bluetooth OBD II device and read my fault codes:

P0166: Engine Coolant Temperature Sensor 1 Circuit Range/Performance
P0135: O2 Sensor Heater Circuit Bank 1 Sensor 1
P0130: O2 Sensor Heater Circuit Bank 1 Sensor 1
P0420: Catalyst System Efficiency Below Threshold Bank 1

All of the above were something to do with the ECT according to my descriptions. Fairly confident, I changed my ECT, using a genuine part from TPS.

I lost quite a bit of coolant in doing so. Because its xmas eve, i havent been able to get any more coolant (rookie error) so ive topped up with water until I can pick up some G12/G30.

The engine seems to be running nicer and my coolant is at a steady 75c according to my OBD, and oil is quickly reaching 90c (I assume thats the water) but not breaking that.

I havent noticed before whether they did before or not, but having read forums I looked and I noticed that my fans wern't turning. I can't get them to turn, no amount of A/C or anything. I was wondering what you all might think to that? Should they be turning at all? Are there any checks I can do to see whether the fans arent working altogether or whether its the ECT or something else?

Thank you!

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Re: ECT Sensor & Fans problem

Post by RUM4MO » Tue Dec 26, 2017 10:08 am

So, you have sorted out the temperature gauge issue that seems to be a typical failure with age, good. It might just be that the B1 S1 sensor has failed as they do tend to fail with age, one suggestion though, while it might sound like a good idea to buy a cheap sensor to replace that one, 9 times out of 10, doing that will solve your problem only for a few hours/days and in the end you will need to buy a proper sensor, they are manufactured by NTK who are an NGK company and so either buy the correct one from an NTK outlet or the same item packaged in a VW Group box from a VW parts outlet.
Remember that this sensor control the "base" fuelling mixture level so it will affect the indicated required trim figures if it is faulty.
Cooling fans, maybe you need to read up on this subject, there is a lot of info on the internet under "VW Golf Cooling Fans" - or some similar sounding search phrase, what normally happens is, either the fan control module, or the fans built in resistor pack(s) is faulty. Other possible issues covering the fan switching for engine cooling is the thermal switch in the water system, or in the case of the AC cooling fan, low or no fridge gas charge.

Once you have found and read the stuff on the Golf cooling fans, you will be able to check which part(s) are faulty and replace/sort them.

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