the flyin' scotsman

my digi dash is reading approx. 10-15C below what it should..........is there a method to recalibrate the sensor/system?

Bilal928S4

Malcolm,
My understanding is that there is no calibration. The sensor actually protrudes down from the bottom of the driver side rear view mirror on the door. I just installed one in my 89. There is no adjustment on the sensor. I don't know if there is any in the digital dash. Maybe you just need to swap in a new sensor.

Tails

Malcolm,
There is no actual adjustment, however there is a temperature chart with equivalent ohm resistance chart contained within the "Diagnostic of the Instrument Cluster" in the Service Information Techniik WKD 495 821 on page 8.

If you remove the temperature probe from the door mirror you can check the resistance against a known temperature to ascertain whether the probe is OK or not. On its removal suggest you clean the probe end as sometimes they have been painted and also spray the connectors with DeToxIt.

If still not accurate enough then need replacement. It is not connected to anything other than giving you the outside temperature.

As another check you can swap the probes over from the other car and see if the reading are similar?

Tails 1990 928S4 Auto, Midnight Blue Metallic & 1990 944 (951) Turbo, Arctic White.

the flyin' scotsman

thx guys......I'll read the Service Info then decide next course of action.

Not really into taking the mirror apart to fix such a minor issue while during the best part of our driving season

Randy V

I have the same problem on my GTS. It used to be accurate but now the temp displayed is usually 5-20 degrees F below actual.

x98boardwell

Wanted to bump this thread.

For some reason mine is showing -40 C all the time... is there a way to reset it or change it? It may just be that I don't know how to properly operate the system. All was good until I removed the motor and then reinstalled... I did keep the wiring harness attached the motor when I pulled it out and fed all the wires through the fire wall but from what I can see below that wouldn't be an issue if actual sensor is inside drivers door. Wonder what is happening or happened?

Anyone else with this issue?

Thanks,
Bryan

Hilton

I find the one in my '89 reads just where I like it. Perhaps you could move to a warmer climate?

x98boardwell

Bump for an old thread and my question above... the last response didn't help any

Bilal928S4

The temp sensor is located at the bottom of the driver side rear view mirror housing. The mirror harness wires run through the door. If you are getting bad readings, you have to take the glass off and see what is happening with the wires. Also can check the readings (ohms) of the sensor at different temps.

Hilton

There is no way to reset or change the temperature reading (without changing sensors, adding resistors etc.)

Malcolm's problem was (probably) the sensor being out of spec. Your problem is the sensor output isn't getting to the cluster. The sensor readings range from 60C (750ohm) to -40C (100kOhm).

Which motor did you replace? The window motor, or the mirror motor?

The problem is an open circuit (or a short of the signal path to ground) - so you've disturbed the wiring in the door, or in the mirror, depending on which motor you disturbed.

You need to isolate the problem - so assuming you men the window motor, the first step should be to disconnect the door harness on the car side (just in front of the door arrestor up under the dash) and check for continuity between the sensor pins and all the other pins in the harness. Then move to the next connector along the circuit, until you know which section the problem is in.

If there's continuity between the two sensor wires, the sensor is intact (and you can measure the resistance against the table in the Digital Dash tec spec book). If there's continuity between the sensor wires and any others in the harness, there's a short.

x98boardwell

The only thing that I did was finally install the hands free microphone up near the sun visor which i fed the wire under the dash and up the A-pillar and removed the A-Panel cover as well and reinstalled.. I wonder if I disrupted something then.

Any chance someone has a picture of what the wiring looks like under the dash? It was working before I removed the fender (another reason entirely) and installed the microphone. Maybe I disrupted a wire or something.

69gaugeman

Rule of thumb is when something stops working after you fixed something else, you did it. Look where the two conditions cross (under the dash) and see what you did. The wiring comes out of the door just under the dash.

the flyin' scotsman

my sensor is out of spec........it reads low but it does read

PHIL928

-40 Celcius is an indication that the sensor is not connected, you might have disturbed a connector when you installed your hands free

x98boardwell

Thanks guys,

Phil928, where is that connecter located?