Coolant Temperature Sensor for VW Golf III

First of all, hello everyone out there, now I'm also one of you .

Due to a problem, I have been searching the internet for some time now, but so far I haven't found anything useful, and I am now trying my luck with you .

Our Volkswagen Golf III TDI with an 88 kW 1.9-liter engine has the following error code stored in its diagnostic system:

00522 - Coolant temperature sensor (G62).
27 - 00 - implausible signal.

I replaced the coolant temperature sensor, but the error still persists. When I disconnect the connector while the engine is running and read the 'coolant temperature value' with VAG-COM, the value changes drastically. So, I assume that all the cables are fine.
VAG-COM displays values ranging from -0.9 to approximately -2°C, even when the engine has reached its operating temperature.
The engine starts very poorly when cold (which actually contradicts the negative temperatures supposedly reported by the sensor).

Do you think the control unit might be defective? What else could be broken? The coolant temperature sensor has 4 pins. Do the signals run through the CAN bus? Or is it a simple NTC thermistor? If so, what resistance values should it have on which pins at what temperatures?

It would be great if someone could help me.
Oh, and one more thing, in case it's relevant to my question: The car has been converted to run on vegetable oil.

Regards,
Bubu.

Hello Bubu,

Welcome to the TDI forum!

Are you sure about the 88 kW? Wouldn't it be more likely 66? Because 88 kW wasn't available in the Golf 3, and I don't think it was available in the other models either.

For the Volkswagen Golf 3, the engine codes would be either 1Z, AGR, or AHU.

Best regards,

Jan.

Sorry, Jan (old acquaintance ), you're right. The Golf has 66 kW, which is 110 horsepower. By the way, it's the Golf Variant.

Regards,
Bubu.

Hello,

How was it again with horsepower and kilowatts?

http://www.tabelle.info/leistung.htm

Best regards, Andy.

Hi Bubu,

66 kW is equal to 90 horsepower.
81 kW is equal to 110 horsepower.

)

Best regards,

Jan.

Hey everyone, don't confuse me like that. Of course, it has 88 kW, which is 110 horsepower. It's the wagon version after all.
'But that issue with the performance isn't my problem; I don't really care about it. What bothers me is that stupid error with the coolant temperature sensor...'
It would be really great if you could help me with that.

Regards,
Bubu.

P.S. It's not my car, but rather my dad's . I know the performance of mine *g*.

Oh, and one more thing, in case it's relevant to my question: The car has been converted to run on vegetable oil.

Regards,
Bubu.

Hello, vegetable oil at temperatures below 8°C??? I successfully used waste oil from a recycling center to fuel my Mondeo, but I stopped doing so when the temperature dropped below 8°C. Or do you have a two-tank system?
If that's not the case, then the difficulty starting should be due to something else.

Best regards, René.

Hi Rene,
First of all, 'thank you' for your contribution.
The difficulty starting the car is NOT caused by the rapeseed oil. We were able to drive in temperatures as low as -10°C with that oil! The car was specially modified for that purpose (with various pre-heating systems, software adjustments, a stronger battery, and two fuel filters, etc.).
It seems to be working well so far, so it probably isn't related to that. According to the VAG-Com diagnostic tool, the fuel temperature reaches around 50°C quite quickly after starting.

I'm particularly interested in the error code stored in the system because it's still there even after replacing the coolant temperature sensor. What could be causing this? How does the engine control unit actually know that the value is incorrect? Could it be related to the fuel temperature (fuel temperature higher than coolant temperature = error)? The fuel is heated electrically in this car (the fuel filter has a heating element built into it). However, this theory is contradicted by the fact that VAG-Com still shows minus temperatures in the coolant after a long drive.

Is anyone else experiencing similar issues? What could be the cause?

Regards,
the perplexed one.
Bubu.

Hello,

81 kW is equal to 110 horsepower.

What did the temperature sensor look like that you replaced, and where is it located in the engine compartment?

"The fact that the engine control unit (ECU) considers an engine temperature of approximately -1°C after a few minutes of driving to be implausible is not really what you're asking about, is it?"

The temperature sensor is an NTC type. This means that if it displays very high resistance values, which correspond to very low temperatures, you should check the wiring and connectors.
Besides that, who guarantees that the new temperature sensor isn't defective?

Otherwise, I would have suggested taking the sensor inside and measuring its resistance when it's at a temperature of 20°C, and even putting it in a pot of warm water. But now, it's probably leaking quite a bit of coolant. So, it can only be fixed with a plug or by using the old sensor to seal it.

Best regards, Rainer.

Hello,
Okay, now I understand that our car has 81 kW. That's why I could never find an oil filter for this stupid thing.

The temperature sensor is located in a plastic tube where the coolant exits the engine. It's made entirely of plastic (the new one has a stainless steel or aluminum front). I'm just surprised by the four connections. Are you sure it transmits the resistance signal? Doesn't it also communicate via the CAN bus?
Connector pins:

1 2

3 4

Resistance between:
1-4: approximately 45 MΩ.
2-3: approximately 45 MΩ.
3-4: approximately 42 MΩ.
1-2: approximately 45 MΩ.
1-3: approximately 2.7 kOhms.
2-4: approximately 2.4 kOhms.


The resistance values change significantly with temperature variations.
Are multiple temperature sensors installed inside the housing? Or why are there 4 pins?

'But why does VAG-Com show a temperature change when I disconnect the connector? Shouldn't that mean the wiring and control unit are okay?'

Regards,
Bubu.

Hello!
Are you sure that it's passing the resistance signal through?? Doesn't it also go through the CAN bus??
Absolutely certain that it's not running over CAN!

Resistance between:
1-4: approximately 45 MΩ.
2-3: approximately 45 MΩ.
3-4: approximately 42 MΩ.
1-2: approximately 45 MΩ.
1-3: approximately 2.7 kOhms.
2-4: approximately 2.4 kOhms
You can probably ignore the values greater than 10 Meg, as they are approximately equal to the conductivity of plastic .

According to your measurement, there are two sensors within the housing, one located between pin 1 and 3, and another between pin 2 and 4. In my opinion, one is for the display in the instrument cluster, and the other is for the engine control unit.

Since both values are roughly the same (within +/- 10%), the sensor appears to be providing plausible readings (at least for temperature).

As Rainer already wrote: Since the sensor is an NTC (Negative Temperature Coefficient) thermistor, low temperatures correspond to high resistance values. To me, this sounds like there might be problems with the wiring, such as corrosion in a connector or cold solder joints.

I would suggest taking a closer look at the wiring, especially the connectors. One person could use a VAG-COM device to read the data (continuously), while the other person gently moves the wires/cables or disconnects and reconnects all of the cable's connectors.

Or directly measure the resistance of the cable.

Here's a basic tip: Always include the engine code; it makes it easier to help you. You can find it in the service booklet. The power output (in kW) is always listed on the vehicle registration document. The year of manufacture is also helpful.

Regards,
Private.

Bububaer wrote:

I'm only surprised by the 4 connections. Are you sure that it passes through the resistance signal?

Hello,

In older rotary valve engines, this was a dual sensor for the glow plug timing control and the temperature gauge. It's probably still the same: one for the engine control unit and one for the display. I've had these things fail three times in total across two cars. When it fails, the thermometer shows cold, and/or the engine control unit complains because it thinks you're trying to trick it with a "cold" message after only 5 minutes of driving. However, a poor cold start must then have another cause, such as a faulty fuse for the preheating system or injectors clogged due to soot (apparently this happens in diesel engines ).
Oh, who actually did the renovation of the toilet?


Best regards, Uli.

Do you think the control unit is defective?

It's rather unlikely, as they rarely break down.


I would suggest taking a closer look at the wiring, especially the connectors. Either have someone use VAG-COM to read the data (continuously) while another person jiggles the wires / disconnects and reconnects all the cable connectors.



The temperature sensor (which actually has two sensors in one) also needs an 'input signal.'
When taking your measurements, don't forget to check if the correct signal is present at the 'input' (usually ground).
We've sometimes encountered similar problems at work (replaced switches, checked cables, etc.), and it often turned out to be a loose or corroded ground connection.

It would be helpful if you could tell us exactly what the cause was.

Hello guys,
Wow, finally school is over again, and I have more time for crafting now.
I've made some progress now.
I've created a diagram for the temperature sensor now. The resistance values are perfectly accurate.
The two ground connections to the temperature sensor are fine.
The positive cable to the temperature sensor for the temperature gauge has approximately 5 volts relative to ground.

'However, the yellow/red cable (the positive wire from the temperature sensor to the control unit) is concerning me. I'm only getting about 3.5 volts out of it. When I disconnect the round engine connector and measure there, I also only get 3.5 volts. I've also tried connecting various fixed resistors (470 ohms, 10 kOhms, 5 kOhms). There's almost no temperature change shown in VAG-COM. The temperature only changes by 3 or 4 degrees (and stays around 1-2 degrees).'
The voltage at the device is approximately 0 volts. Could there be a high contact resistance somewhere that's causing the entire voltage to drop? Theoretically, this resistance would have to be in the kilo-ohm to mega-ohm range. My measuring instrument has an input impedance of greater than 1 Gigaohm. Therefore, my suspicion is that there's a relatively high contact resistance somewhere that doesn't significantly affect the measurement at 1 Gigaohm, but when a 10 kOhm resistor (fixed resistor) is connected, the voltage drops.
Where can I find the control unit? Where does the yellow/red cable go? Based on the cable routing, it seems to be heading somewhere towards the footwell.
Why did VW wrap that area with such unsightly black electrical tape? The electrical tape makes it extremely difficult to trace the wiring.
Okay, for me, the most important thing right now is to figure out where that yellow/red cable goes. It should be connected to the control unit, but how do I find it?

Wow, thankfully I still have a nice, clear, and easy-to-repair 021A ).

Thank you for your help.
Bubu.




Oh yes, and we had the conversion done by them:

United Workshops for Vegetable Oil Technology.
2 Am Steigbühl.
90584 Allersberg-Göggelsbuch.
Phone: 09174/2862
Fax: 09174/2521




Other companies:

Hilmar Wolf.
Ringstraße 28
97508 Unterreuterheim.
Phone: 09729/6948

Elsbett Technology GmbH
15 Weißenburger Straße.
91177 Thalmässing.
Phone: 09173/77940
www.elsbett.com

Georg Lohmann Prototype Construction.
12 Welfenstraße.
81541 Munich.
Phone: 089/484837

Where can I find the control unit?
Inside the water reservoir compartment. Remove the windshield wiper arm and cover --> The box with all the cables is your target.
Where does the yellow/red cable go??
Wahrscheinlich genau dort hin. Wenn du meinen Tip beherzigt hättest und Motorkennbuchstaben (MKB) und Baujahr angegeben hättest, dann hätte ich auch für dich im Stromlaufplan nachschauen können. So lneither.

Regards,
Private.

Hi Private,
I just checked the documentation, and it says the engine code is AFN.
Is that the letter code you're looking for? It would be great if you had wiring diagrams.
Thank you very much for your effort.
Bubu.