I have noticed the computer readout for average fuel consumption and avarage speed appears to reset itself everytime I start the car.

If I remember correctly (I have had the car for over 10 years) the average readings used to be stored and would only be reset when I pulled the reset lever and held it for a short while.

Is there some sort of reserve/rechargeable battery that needs replacing?

A further question - if the computer is re-setting itself is this also likely to be happening with the engine management computer? Or is that a separate issue?

The car battery is around 3 years old. Could a voltage drop on starting be a cause?

The car is a 88 S4 Auto - Euro

Thanks in advance for any input

 

Still no replies - any suggestions?

 

Peter,
The main ECU's (fuel etc) won't reset unless the battery is disconnected.

I don't know about the dash, but I am pretty certain it won't have a back up battery. It would be fed with a permanent positive from the main battery.

Low battery volts at cold start should show up as a fault code on the LH ECU. Code 1111 . You rcar has diagnostics, so you can always check, assuming you have a suitable lead/tester.

Regards

 

continueinsturmentdefinateohmetersatisfactorly

 

Hello Peter. It's always a treat to see another Japie Rennlister.

I live in Cape Town though at present I'm on a ship in New Orleans.

I have the 89 GT and IIRC my trip indications would always start on the previous settings unless I held back the control stalk or zeroed the counters. A possible test would be to stop the car, take all the readings with engine running then stop the engine and immediately restart it. If the readings reset to something different you have a fault.

Unfortunately my instrument cluster is out of action and in pieces right now due to (I suspect) a faulty circuit board so I can't check it for you. I can tell you that there's no little battery in there. However Pomona Parts in JHB told me they know of a fundi who works on Porsche instrument panels.

Best of luck
Colin Beard 89 GT

 

Peter,

Peter,

My previous two attempts have failed. You can see my first failure from my previous message, so I will see how I go this time, third time lucky.

I had a fault in my instrument cluster in that my odometer No.I would reset by itself after a short distance travelled. As you are aware each time the engine is restarted the RHS of the computer print out resets itself to odometer No.1.

If I toggled up odometer No.II it would also reset by itself and if I toggled up my stopwatch I have difficulty in operating it, that is starting it, stopping it and resetting it to zero by pushing the LHS push button. As a matter of fact it would stop by itself and I could not reset it and it would then reset by itself.

In addition when I tried to reset my average fuel consumption by pulling back on the 4 way information switch shaft for 3 seconds it would not reset, but if I disconnected the main battery it would reset.

As you are aware the push button switch located on the LHS of the steering wheel on the facia of the dash zeros the odometers and controls the operation of the stopwatch and the 4 way information switch zeros the average fuel consumption and the average speed.

It took me 7 months of fault finding to locate my fault and I would suggest that you have a similar fault. In my fault finding I removed the instrument cluster 3 times, I changed over my reset push button with the intense washer push button switch on the RHS of the steering wheel and I proved that the operation of the buttons worked in the intense washer circuit.

I also removed the circuit board from the instrument cluster and replace blown instrument lights and generally carried out some routine maintenance and cleaning of the circuit board, I cleaned up the circuit board contactors and there respective 4 off plug connectors.

I removed the 4 way information switch and checked out its continuity and open circuit functions of the 4 contactors within the switch by a multimeter ohm resistance test and all appeared to be in order. I even disconnected all terminal blocks to the instrument cluster and checked the wiring and contacts as well as cleaning all earth connection, but still the intermittant fault remained.

I even tried to purchase a bridge piece to under take my own instrument cluster diagnostic test, however, after finding which pins to cross connect and before I went down this track I decided to check the 4 way info switch again as my fault finding logic kept pointing to this switch.

I removed the switch again. Access can be gained to the back of the switch via the removal of the clear plastic cover. When opened, this time I measured the actual resistance across all the four contacts and I found that the reset contact (for the average fuel consumption and the average speed) had a much higher resistance than the other three and by this I deduced that the resistance was high enough to fool the computer that the contact had been opened circuited.

The four fixed contact in this switch are "l" shaped and the moving contact is a flat spring steel contact. I burnished the faces of the contact with a fine jewelers' file and then I checked that the contacts made a good contact via the multimeter resistance reading and I also checked that when the stalk was pulled, pushed and toggled up and down that it actually opened the contacts.

As you know the average fuel consumption and the average speed can be reset by disconnecting the main battery, however, when I was inside the instrument cluster and I have checked the circuit diagrams for the instrument cluster and senders , sheet 4, I have never located or seen a battery indicated. This does not mean that there is not a battery installed somewhere?

In closing I would suggest that you check the 4 way information switch as described above as I believe it will solve you problem.

If you need any further advice please reply via this forum.

Tails 1990 928S4 Auto

 

The first sign of a bad connection or a failing battery is usually the resetting of the dash.

Low cranking voltage will cause a reset. My '90 GT did that for several months before the battery finally died. Hasn't done it since the battery was replaced.

 

Your 88 has a digital dash? Haven't heard of one in anything earlier than an 89. Must be a very late 88 production.

Voltage drop causes the reset just like Wally mentioned. Check your battery and ground connections if your 100% sure the battery is good.

 

Gents (and ladies?)

Thanks for the replies - I think the problem may well be a failing battery and the resultant voltage drop. The starter is definitely a bit more sluggish than usual.