Yes, but the number goes down disturbingly quickly!

 

Sorry to resurrect this thread, but I am retrofitting the OBC to my January 1992 UK 964 C2 Manual. All the functions work except for the outside temperature which reads -40C. Given that my car had the two connectors in the loom (for the stalk and the tacho) should it have had the outside temp sensor too? Or do I need to add one to the right-hand (RHD) mirror? And, if the fuel consumption information comes from the ECU, why doesn't the OBC use the ECU's outside temp sensor?

I've seen previous posts about the temp sensor wires being reversed during aero mirror conversion, but I'm 99% certain mine had aero mirrors from the factory (it definitely had 16" Cup wheels), but they may well have been removed for paintwork etc.

Shall I carefully pull the mirror of it's backing to see what's behind?

Thanks for any suggestions.

 

I did this on my '90 C2. There was no temp sensor or mounting bracket for it in the mirror. I was updating to aero mirrors at the time and found that there was no wire for the temp sensor in the '90 harness to the mirror (#28-30 in the diagram). Instead of going to the trouble of running a new wire through the door loom, I ended up mounting the temp sensor that I bought at the front intake area of the car. In hindsight I might have taken the time to do that as the temp reading at the front left area is sometimes affected by heat from the AC radiator.

Good luck

Jim

 

Thanks, Jim. I hadn't seen your parts diagram before. I have ordered the sensor (it's a 928 part). I can feel two holes on the bottom of my aero mirrors. One is for the release, the other I assumed was a drain, but the tip of the sensor can go there. I might stick it rather than use a bracket.

The next question is where did you run the wires to? Somewhere on the ECU or to the back of the OBC? The multi-connector on my OBC looks like it must have the wires already, so do I need to find where they terminate at the other end?

Thanks
Paul

 

Paul,

I did this back around 2005 so details are a little fuzzy... I've attached the section of the schematic that shows the OBC and temp sensor detail. You can see that the temp sensor wires connect to pins 8 & 10 at the back of the OBD equipped Tach and run to a three pin connector T12 which I believe is on the harness within a foot or two of the Tach on the way to the door loom. The issue is, my car is LHD and yours is most likely RHD so I'm not sure how that translates re cable routing. Also, since your car is a '92, they may have changed the wiring harnesses slightly.

In any case, I think that T12 connector was equipped but had no wiring beyond that point to the door loom. I remember splicinging to the wiring at/near that connector and running it to the front left of the car through bulkhead grommets provided for wires to the frunk area. I have read posts by at least one person who extended the wiring into the door loom and out to the mirror. If I recall, I made my location decision because there were no spare wires I could find in the door loom to convert to temp sensor leads and fishing them in seemed a bit daunting. Also, this got messy at the mirror end because the non-OBD optioned aero mirror was not equipped with pins or connector capacity for additional wires for the temp sensor.

At that point I took the easy way out and extended the wires to the front of the car. You will obviously have the Tach out to do the swap so you will have reasonable access to the cabling to check out your options.

Good luck!

Jim

 

Thank you. I’ll look for that connector. There is another connector near the OBC stalk, but that’s probably for cruise, but it must be elsewhere under the dash or behind the tacho.

 

I've just been out for a 15-mile drive since fitting the OBC. My observations:
The trip odometer is quite accurate- 15.2 digital versus 15.25 analogue.
The average speed feels right- 34 MPH.
The fuel consumption feels right too- 23.3.
I couldn't zero the remaining distance on the fuel of course, but after a few miles it adjusted and reads 125 miles with the analogue gauge halfway between the 1/4 and the reserve.
BUT the digital speedometer reads about 11% over the analogue! My analogue speedo is scarily accurate against Waze’s GPS- maybe +/- 1 MPH, so it's such a shame the digital is so badly off. Is this what other experience?

 

The other hole in the mirror is for the sensor, there is no drain

My digital speed is a little out compared to the needle too.

 

11% off is a bit high, the OBC and speedometer readings are normally the same. Normal deviation is 3 to 6% high at 50 to 80km/h (30-50MPH) This is an intentional offset to cover temperature drift, wheel size circumference/wear etc.
The offset/eviation is not linear over the scale. I seldom see speedometers showing the exact same speed as GPS measurements. Maybe the speedo instrument has previously been adjusted or modified.
Cheers,
Tore

 

Thanks, TakeFour and ToreB. I can live with it- it's 35-year-old tech, after all, and just a bit of fun to have.
My analogue speedo was rebuilt recently, so that might help.
It's just odd that the digital odometer isn't 11% higher than the analogue too. It suggests that the distance is correct but the clock is out.
Tore- it's interesting what you say about temperature drift... I wonder whether it will improve when I have the temperature sensor connected?

 

I'm not ready to give up on finding the temp sensor wires in the door... My OPC has confirmed:

Mine is 1992, so in theory, it must have the wiring. This is Vifa's photo from another thread from 2007(!). What I'd like to understand is whether the two purple wires for the sensor terminate on pins just inside the door, or do they somehow share the multiplug for the aero mirror?

Has anyone with OBC, RHD ever dropped their aero mirror off for painting and can remember whether there was one or two connectors?

 

That is odd my car 91C2 Tip the analog speedo reads a good 10 mph higher than the digital in the obc which is very close it. The analog higher the speed the more its off

 

Are the two trip odometers accurate? Mine are spor on, which suggests the clock varies in the OBC- that would cause mine to read over analogue and yours to read under.

I don't suppose you've ever had cause to take off your door mirror with temp sensor and noticed whether there are one or two connectors?

 

One big round connector you need to pop the pins out of to remove the mirror. I want to say I’m not sure I ever thought of comparing odometers trip meters.