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VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old April 2nd, 2012, 10:50   #1
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Join Date: Jan 2009
Location: Edmonton, AB
TDI(s): TDI-free
Default Engine Coolant Temperature Sensor

I have in my garage an Engine Coolant Temperature Sensor (http://img.eautopartscatalog.com/liv...1623711ELT.JPG). It is brand new and unused, and I want to find out something about how exactly it works. Specifically, does anyone know what the pinout is? Is it a discreet on/off at a specific temperature?

Unusual circumstances are leading me to using this part in a way that is different than it was originally intended.

Back in 2009, I had an MIL issue on my 2003 TDI. This was part of what I was going to remedy it with, and the parts had arrived just prior to a planned trip. Part of the planned trip was to take it to the dealership where our friend works for a timing belt change; we get employee pricing, and this dealership was one rare one that had a good reputation, and I figured I'd just bring the parts along and they could replace if warranted. Well, the start of the trip came to an abrupt stop literally, as the Golf was totalled enroute. The car saved our lives for sure.

The parts made it back home to sit in the garage, with no TDI to eventually find a home in.

Fast-forward to today. I have a pop-up camping trailer with a three-way fridge. The fridge is a gas absorption unit that can be powered by 12VDC battery (only while towing as it would otherwise run the battery down very fast), on 120VAC plugged in to shore power, and on propane mode when no power source is available.

My personal challenge is to install three indicator lights (must be LED for the lights that require the 12V battery), that will quickly tell me which of the three modes is currently on. The two electrical indicators are easy enough to handle. It is the gas mode light that has me searching for a soloution. It should be relatively cheap. My original line of thinking had me looking at thermocouples and thermopiles, but those were problematic. I couldn't find an LED that could be powered by the output of the thermocouple, and a thermopile was getting up in price, and I still couldn't find an LED that would illuminate with the voltage output.

This led me to thermal switches - and that in turn led me down the road to looking at automotive ones. Specifically, a cooling fan switch, that could be attached to a strip of metal to be heated by the flame. The light comes on when the flame is running, and goes out when the flame is off. Perfect for indicating if the flame were to blow out or if I ran out of gas.

Then I remembered my Engine Coolant Temperature Sensor sitting in the garage collecting dust.

Any help with someone who knows the specifics of how this sensor functions? If not, I suppose I can play around with my multimeter and a 12V source, but I would rather just know the pinout from the get go.

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Old April 2nd, 2012, 12:36   #2
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Join Date: May 2009
Location: South Africa


You are over complicating things - get a bi-metal thermal switch (simlar as used in toasters and microwaves), get the flame on the switch, it will disconnect when the flame is on it, and reconnect when off. Connect the switch to a battery and an inverter to trigger an LED. BTW, whatever you do, you will need some electronic circuit to control the LED, even using the car's coolant sensors (is just a thermistor with an analogue output, high at low temperatures, low resistance at high temperatures). I'll go for the bi-metal switch, the gas flame will kill standard solid state sensors. Cool idea though.
Silver VW Jetta A4 TDI 2002 AHF, 421 000km, MAF and EGR delete
(VCDS Hex + CAN, ALH/AHF tools, BRM/BXE tools)
White VW Jetta A5 TDI BXE, 505 000km
Jettascuba is offline   Reply With Quote
Old April 2nd, 2012, 14:37   #3
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Join Date: Jan 2009
Location: Edmonton, AB
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Thanks, I will abandon using the Engine Coolant Temperature Sensor. Searching "bi-metal thermal switch" (thanks for the name, it worked much better than just the "thermal switch" I used earlier), I came across this, which I can get locally:


Sounds like the ticket.

As for the parts, they'll sit some more, I guess. Unless anyone here is looking for the temp sensor (and o-ring) as well as a MAF, all brand new (packages slightly damaged from being torn by things thrown around in the car).
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