temp sensor/guage query

[nrxx]

Hi
1987 1.9 DG
Had a non functioning temp guage for a while now, did work but hada few weeks of low readings and now nowt. Got a new sensor for side of thermostat housing, checked for power, ok. Changed and made no difference. Noticed another sensor hidden around the front of the stat housing. Should I have both of these and if not, which one should be coolant guage sensor? Haynes appears to say that the one I changed should be a fuel injection temp sensor and that the one hidden round the front is the one I want (obviously with a DG I don't have injection!).

Also... Do I need to remove the actual instrument cluster to check the multi-pin or just the cover?

Thanks
Nick

[AngeloEvs]

The Temp Guage Coolant sensor faces the front of the van. This is the one you need to change and make sure its the correct one identifiable by its colour. Multi-connector problems (if suspect) are best diagnosed with the dash out. The copper edge strips on the flexible part of the membrane panel need to be inspected and connection 6 to the Temp guage needs to be checked for continuity. First, try shorting the Green/blue wire that connects to the temp sender (cab facing) to the engine block with a short section of wire and switching the ignition on. Gauge should start to rise after a few seconds and the coolant LED should flash continually.

There is an easier test for Post '86 Vans that have the Level Sender control Unit in the fusebox.

The gauge and its calibration can be checked by removing the module marked 43 (or 42) from the fusebox. Using male spade connectors with a short link of wire (pic shows a 100 ohm resistor for testing calibration but wire is fine for a simple yes/no test) place them in the socket locations as shown. This will connect your gauge to earth and you won't have to crawl under the van to check the dash/guage is Ok.

The vacant socket view shows the relevant connections to the LSC (Level Sender Control) module. Note that the Earth connection for the LSC module terminates at the Earth cluster mounted on the Pillar next to the Fusebox ans is a common source of Coolant LED flashing problems. Before checking the gauge check this connection to a known earth and if poor readings are obtained then check the cluster.

The connections from the Gauge to the coolant senders (Temperature and Coolant Level) are via the multi connector in the engine bay (location of connector Box shown in the inset) and these should be inspected too.
Calibration of the gauge should be carried out and checked with this disconnected and a 100 ohm 1W resistor placed as shown below. Gauge should settle to one needle width left of centre + or - one needle width.

[nrxx]

Hi , thanks Angleo, couldn't ask for a better reply! I'll have a run through this pm.
Nick

[AngeloEvs]

all the best, I made a mistake with the colour code, I said it was red/yellow but is actually blue/green....oops!

[nrxx]

Hi Angelo

Done all the tests as described and all point to a faulty sensor. Thanks for the help, particularly the fusebox jumper. All I have to do now is order another new sender!

Thanks again

Nick

[nrxx]

Hi Angelo
All done now. New sender fitted and guage now working. Was only reading c1/4 but after towing wifes car it now seems to read c3/4! If I remove the relay and bung a 100ohm jumper in and turn ignition on will that calibrate or do I need to disconnect something (the guage?), as you suggest above?
Thanks for the help to date, oh, and happy new year!
Nick

[AngeloEvs]

Just connect the resistor as described above with engine cold if leaving the sender in circuit. I disconnect the multi connector in the engine bay (as shown in the picture above) to prevent the temp sender from influencing the calibration readings. Mine reads one full needle width from the left of the LED with the above calibration test and sender isolated. VAG spec tolerance for temp and fuel gauges is + or - one needle width so don't be alrmed if it reads higher or lower by that margin. Happy new year to you too and all!

[clartsonly]

errmmm does this "calibration" actually change the "normal temperature" position of the needle mine always read 3/4 to almost full temp once warm the fan still cuts in at the front if it is idling after a long drive. can I calibrate my sensor even in a 1985 version?

thanks for anyhelp, I assumed the thermostate was knackered and staying closed too much

[AngeloEvs]

The test is purely to check that the temp guage is within VAG specification. It will not re-calibrate your guage but will highlight if the guage reads lower or higher than it should. VAG use a a similar test using a range of fixed value resistors to check the Petrol and Fuel guages at three points. For the Temp gauge this is Warm - Normal and the threshold of Overheating that triggers the warning LED (47 Ohms). The 100 ohm resistor is based on the value of a typical senders resistance at 100 degrees and the best (and closest) I can come up with for checking the accuracy of a guage at around normal operating temp. I have checked four Temp guages and they all read about one full needle width left of the LED ( slightly lower in one case but within the VAG spec).