Tails

My stop watch and odmeter I & II are self cancelling without pushing the reset button.

This was first noticed when the odometer I started to reset by itself and when changed to odometer II with the stalk it also went to zero. When the stop watch was selected it would only run for a few tenth of a second and then reset.

The odometers would only register two tenths after resetting and then reset to zero.

The odometers and the stop watch work OK when they are not on display, however, when selected they all cancel to zero after a few tenths of a second.

I have removed the reset button and dash elumination module and disconnected the dash lighting adjustor from the module and also the four wires into the odometer reset switch which allowed me to remove the reset switch to my work bench.

Dismantled reset switch, by removal of the white internals from the module body and was then able to remove the circuit board contain reset switch and icon elumination light. Cleaned circuit board around soldered joints and generally gave it a good dose of WD40.

Reinstalled and all appeard to work OK after reconnecting battery, however on a long drive yesterday odometer I, which is automatically selected when car is started, again reset itself to Zero as well as II and the stopwatch, so back to the drawing board. However this time the stop watch would not operate when the push button was pressed.

Tonight again removed reset switch as the push button did not appear to be activating the reset set switch.

Confirmed that the travel on the push button was not activating the reset switch, so lengthened the cylinderical reset switch activating rod and got the reset switch to activate.

Measured the resistance of the four wires on the reset switch and found the resistance between wire one and two counting from right to left, looking down on the switch, was maximum resitance and when the switch was activated the resistance was reduced and after a couple of seconds returned to maximum. All measurements of resistance between 1 & 3 , 1 & 4 and 2 & 3, 2 & 4 all showed maximum resistance.

Checked the continunity of the wires which connect to rhe reset switch and wire between 1 & 4 only show a lower resistance indicating they are possibly connected in the circuits somewhere.

Reassembled the switch and reconnected etc., took the car for a test drive and the symptons are still the same.

Have checked circuit diagrams, but unfortunately not very helpful. I would suggest that if I go to OPC will be advised to purchase a new module.

Has anyone had similar problems or any suggestions to rectify would be welcome.

Tails 1990 928 S4

<img src="confused.gif" border="0">

Alan

Tails,
Seems like you really need to determine what is causing the problem. You seem to have zoomed in on the switch - it may not be this...

I'd suggest you remove the switch again tape up the wire ends and drive around for a while (up to a few days) and see if the reset issue still happens without the switch in circuit.... If yes the switch is not the culprit. If its fine without - look to replace the switch.

If it happens without the switch it may be the wiring (check for damaged insulation - rubbing against something) or it could be some kind of gunk on the circuit board/connectors for the OBC/info system (resistance path). Or worst case could be you need a new OBC module.

I'd get into diagnostic mode on the rest of this stuff ASAP.

Alan

Tails

Alan,

Thanks for the information.

Continued with fault finding and decided to take the pod off and check wiring etc for faults.

Located that the PO had been into the wiring before me and had a jump wire from the rear window demist unit to the pod illumination reostat.

When first got the car found that the demist switch was not working correctly, so pulled it apart to repair and now works OK for heating rear window and rear view mirrors as well.

Replace blown illunination globes and now have fully operational lighting system in pod.

Could not find any wiring fault, however cleaned up wiring, cleaned earth connnection, secured connectors correctly etc and reassembled, but fault still remained.

As a final thought changed over high intensity windscreen washer switch with odometer reset switch and now all appears to be working OK in cluding high intensity windscreen washers.

Don't want to jump to final solution, as proof will be in how long it works without resetting, but been working for a couple of days.

Alan, thanks for the help.

Tails 1990 928SS4

Kevin R.

I am reopening this old post as I have the same model and a much BIGGER electronic dash problem.

What is the ultimate dash display issue? To have NO DISPLAY at all.

That's right. Fuses and grounds are all good. I am amazed the car even starts and runs as obviously this is mostly for driver information feedback only and does not affect engine electrical and mechanical.

So here is the status of the following:

DIGITAL DISPLAY: not working
ANALOG GAUGES: not working (except for Voltmeter)
CRUISE SWITCH: not working
CLOCK: not working
INFO SWITCH: not working
WARNING LIGHTS: occasionally ALL come on when shifting into "3" or "R".

What do we have going on here? Has anyone ever had a total failure of the dash display?

Kevin
1990 928 Auto

Ed Scherer

Have you had the instrument cluster out? With that much stuff failing, I suspect a disconnected connector at the cluster or a grounding problem.

If you haven't had the cluster out and want to tackle that job yourself, see 15 minute instrument pod removal update and instrument light bulbs for an OK price.

Nice thread resurrection, BTW.

Also, when you get it working again, since you'll be familiar with instrument cluster removal anyway, consider Converting Porsche 928 Interior Lighting to LEDs (which you might want to review anyway, as it contains some additional instrument cluster removal/reinstallation tips); see also the earlier related thread Interior LED Changeover (uhm...Looooong).

Leon Speed

Make absolutely sure fuse 39 (counting from the left) is ok. Take the current fuse out, clean the terminals and put a new fuse back in. Sometimes a fuse might look good but have bad contacts.

mitche

I have exactly the same problem, I just got my dash back from restoration 350€ and same problem accurs...

Is there any possibility to measure the dash connectors?

Cheers
Mike


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928 S4 1989
914 1973
911E 1972 Targa
993 1996 Coupe