Temperature Gauge Malfunction - VW Golf G3 TDI 94

Hey everyone,

First of all, I have to say, you have a great forum here! Even though I've been browsing for 3 hours and still haven't found anything to help with my problem! But maybe one of you might have some advice!

I'm going to try to explain the problem now.
As the title says, I'm having a problem with the temperature gauge on my speedometer!
She's acting completely crazy! It started with the display showing only 80°C at some point!
After that, I replaced the thermostat, but it didn't make any difference!
"So, I took my car to a local independent garage. He took me for a test drive and used a diagnostic tool, the 5051 (if I remember correctly). It definitely showed a value of 87°! That made me feel relieved, because you know that the readings on the speedometer also have a certain margin of error."
Last summer, I drove 650 km by car to the VW-Jam in Luckau! Everything was fine then. But then the car was parked in terrible rain for half a day. It was pouring like crazy!
The next day, when we were about to drive home, things started to go wrong after about 5 kilometers! The overheating warning light started flashing wildly, and the temperature gauge rose above 130°C!
"Of course, I immediately stopped and we checked the water hoses! Actually, they all seemed normal. When I turned the ignition back on, there was a brief pause, and then it started up again. I checked the hoses again, and since they were okay, I drove the 650 km home with a flashing temperature gauge!"
However, the problem was with the aftermarket oil temperature gauge! I connected it normally to an original VAG oil sensor located in front of the oil filter, and of course, to a switched positive terminal. As soon as the ignition was turned on, it showed its readiness by the needle initially rising from the zero position to 50°C. But then, when the temperature gauge started blinking, the oil temperature gauge completely stopped working, even though it was only connected to the switched positive terminal. However, the rest of the car was functioning completely normally.
Once I got home, I grabbed a wiring diagram and replaced all the parts that I thought might be related to the temperature gauge. These included:

- Water temperature sensor on the cylinder head.
- Oil pressure sensor
- Oil temperature sensor (the standard one located on the engine block)

Since it wasn't getting any better, I asked a friend what else it could be! He said it might be the tachometer unit.
- Speedometer replaced --> no improvement.

Then he brought a special cable to measure the wiring harness from the coolant temperature sensor to the control unit! --> Everything was fine.

"Now, in the winter, I'm having the problem that the car starts extremely poorly in the mornings because of the incorrect temperature reading it's obviously getting somewhere. So, I suspected it might be the control unit and replaced it, but that didn't improve anything either!"

And this problem is now even driving my regular mechanic crazy, and I'm starting to lose it too!
If anyone has any idea why this stupid ad is malfunctioning and how to fix it, I would appreciate any answers you can provide!

Sorry for the long text, but I thought it might be better if you know exactly how the error obviously occurred!


Greetz Piggel

Hi,

Have the ground connections (e.g., for the motor, speedometer, etc.) been checked?

zaydo

Yeah, I've almost cleaned all of those too! But unfortunately, it hasn't improved anything so far!
I'll finish the rest this weekend!

Hold on, the 1Z engine, like many other engines, has two sensors. One for the display (G2) and one for the MSG (G27). It seems that in your case, the G2 sensor isn't always working as it should.

Which one was replaced? The two sensors should be able to be simulated using potentiometers to check the wiring. One of them is displayed directly on the combination instrument, while the other (G27) needs to be checked via OBD.

By the way, I'm going to replace the speedometer/MSG/some sensors based on suspicion... would you like to donate a few euros to a good cause?

Both are located in a housing in front of the cylinder head, inside the coolant passage.

Best regards, Robert.

@gerbi,

I bought the temperature sensors new; they weren't too expensive! I found the MSG on eBay for 40€ and the speedometer for 30€! Otherwise, I wouldn't have done it.
Based on the wiring diagram, it seems like G2 and G27 are located in the same sensor! Is that the one in the black flange at the front of the cylinder, or am I mistaken? I bought a new one once, and then I even borrowed another new one to try, but the problem remained the same!
The cables to the MSG were tested for continuity using a special cable from VAG, and also measured for proper resistance.
However, I just remembered that we did this with the engine not running! So, it's possible that the cable is fine when the engine is off, but malfunctions when it's running, or am I wrong? The problem doesn't occur when the engine isn't running either!
Oooh man, you see how this problem is slowly driving me crazy! I'm forgetting the simplest things!!
Okay, then we'll try it again, maybe I'll be smarter this time!

Quote:

As far as I can tell from the circuit diagram, G2 and G27 are located in the same sensor!

Okay, I can't see your engine, but on some of the older models, there were definitely two sensors installed. Since they have different names (G2 and G27), I suspect there are two separate sensors here.

Quote:

Actually, I just remembered that we did this with the engine not running!

Then it's possible that the cable is fine when the engine is off, but malfunctions when it's running, or am I wrong?} Since the error doesn't occur when the engine is not running!!}
It's certainly possible that a cable could get pinched or damaged somewhere during engine operation. However, if it was "checked," it likely only underwent a resistance or continuity test. These tests are only performed when the system is de-energized, meaning with the ignition off. Additionally, the MSG (presumably a module or sensor) should be disconnected, as it could potentially be damaged in the worst-case scenario.

I don't know how it is for the other 1Z engines, but in the 1Z engine in the Audi 80, there are two separate sensors. One is located on the large flange connected to the radiator, and the other is on the smaller flange (the front of the cylinder head) connected to the heater. The one on the large flange is likely for the engine control unit (ECU).

@wolfi_b,

Is the connector for the radiator on the Audi 80 2-pin or 4-pin?
Mine has 4 pins!

Hi,

bei AUDI kenne ich einen 4-poligen nur aus dem AAZ. Müsste blau/weiss sein. Bei VW müsste dieser im AAZ und 1Z schwarz/grün sein. Der is for AI.

Normally, assuming no climate control is active, the AUDI 1Z has a 2-pin (blue) connector for the MSG (Multifunction Steering Wheel) and a 3-pin (gray) connector for the KI (Instrument Cluster). I'm experiencing similar problems, although not as severe as yours. The KI is showing a temperature around 70°C, and as soon as the sensor for the MSG is connected, I experience significant engine jerks/stalls when driving at a constant speed. I'm currently driving without the sensor to test, and I haven't experienced any jerks/stalls for the past two weeks. In my case, the sensor housing detached from the upper part.