LFA

Experiencing a problem with the coolant temperature gauge in the instrument cluster. ( 1991 GT)

the problem is; The coolant temperature gauge is not moving, not even a bit, on ignition. No movement even when the fans start blowing when the engine gets hot.

We disconnected and short circuited the temperature sensor connector pins seperately on the water bridge and the needle goes to max temp and warning light and signal is on. ( by short circuiting I mean ground connection to either of the two pins of the connector) ( The needle goes to max when you short circuit any of the 2 pins, isn't this strange too)
The water bridge was powder coated, checked if the sensor has ground connection, (if it needs ground to operate) and it has ground.

The temperature sensor is brand new from Porsche ( VDO), tested this part on another 928 and it works perfectly in this other car.

The gauge works when connector pin ( any of 2) short circuited to ground.
The temperature sensor is brand new and working on another car,
What could be the reason for the gauge not moving??

Could the gauge in the instrument cluster be faulty ( even though the needle moves to max on short circuit). is there an easy way to test the gauge in the cluster without removing and dismantling the instrument cluster.

Thanks for all your help,

dr bob

For giggles, stretch a piece of wire from ground to the base of the sensor, and see if the gauge starts working. I've seen some crazy symptoms around what looks like ground on a PC'd water bridge, and what's really ground. There should be NO power-coating in the sensor hole in the water bridge, for instance, so you may want to chase those threads some with a tap just to make sure. Then clean any PC from under the mounting bolts; testing to the bolts tells you the bolts are grounded OK but doesn't tell you about the water bridge casting itself. You'll find out quickly with the jumper from real ground to the threads on the installed sensor.

LFA

Thanks so much, I will definitely try that

The coolant temperature sensor has two pins, I am trying to understand their functions.
The connector could be mounted only one way. So they are not for the same function. When you ground any of these two pins, the coolant temperature gauge in the instrument cluster goes max level. You would normally expect only one of these pins should be linked to the gauge, but that is not the case I guess.

Ducman82

one pin is for the gauge, the other is for the warning light. how do the connectors look?

LFA

Thanks,

The connector is Ok, I even replaced it with another one and the problem is not solved.

One question on the digital 89+ clusters; When you put the ignition on or start the car does the coolant temp needle move a bit or does it stay at the left end without moving even a bit. Before removing the pod and the cluster ı want to make sure whether the gauge is Ok or faulty.

LFA

When I ground the the pin of the connector the needle goes to max. Could the temperature gauge still be faulty when it does this.
İs there a reference to check the voltage or resistance at the connector when hot /cold and temp sensor installed.

FLYVMO

Evren,

Do you have access to the Digital Dash Diagnostic Manual? I believe it is on the famous CD, name escapes me at the moment. I believe all three major suppliers sells it.

If not, I have it in PDF format, the file size is about 5.5 MB.

Cheers!
Carl

FLYVMO

Here are the cluster values and codes for the engine temperature:

LFA

Carl, thanks for your message
I unfortunately do not have the manual. İs it possible for you to email it to me.
My email is evren.ertay@gmail.com.
I am hoping to sort it out without removing the pod.
Thanks and best regards

LFA

Carl, Thanks for posting the data, just saw that

FLYVMO

Should be in your inbox any time now

Cheers!
Carl

LFA

Thanks Carl, very much appreciate your help.
Best,
Evren

LFA

Problem solved;
The 14 pin connector sequence was wrong, top Pin 5 should be Br/Gn on 91. (When searched on the forum before the info I found was; pin 5-Blue/green.)
The temperature sensor has two pins, one is the sender which goes to pin 15 on Plug 4 of the instrument cluster.
The other one is the ground and goes to pin 4 of Plug 4 of the instrument cluster.
Plug 4 pin 4 was not connected due to 14 pin connector with wrong sequence.
That was why the gauge was working when one of the pins were grounded.
Thanks for all your help,