355 Speedo coolant temp oil pressure went off

Can't see any relationship between the three other than fuse 24 in the footwell, but that would cause a lot more problems.

You would lose fuel quantity, most of your warning lights, F1 gear display (?), tachometer, HVAC, Suspension, etc.

I assume the car runs.

All the wiring for these 3 goes through the waterproof connector near the left rear strut, but if that was loose, you would lose your alternator, HVAC compressor and starter motor.

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Not to be confused with the F1 system plug which looks similar.

The wiring also goes through connector 41024

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If that was loose, you'd get no fuel quantity, suspension issues, possible seat belt warning issues, alternator, tacho and some warning lights not illuminating.

It's hard to imagine either of these plugs coming loose.

Tricky one.

 

F1 diagram here:

https://www.dropbox.com/t/CVTJIYl30wz94UU1

 

Did you mean the oil pressure light ... or the oil pressure gauge? If the oil pressure light, that would isolate the fault to the dash (but still separate plugs on the dash)

 

Check the instrument module. There are a bunch of connectors and stuff to go wrong.

Hah, I "finally" broke my car. That is an understatement of the decade. I remember the cylinder head, the fuel injectors, and the on-line lessons for how to use a borrowed oscilloscope.

 

It seems odd that more than one connector would fail at the same time. Even the same fuse power comes in on different plugs.

 

Given that your car recovered almost immediately, I just seems odd that it would be a loose connector. I think the clips on those two white plugs are pretty good. 41024 and 41025.

Do you have a new footwell relay panel? I could imagine a violent shake affecting an old panel. Check relay fitment.

 

So they did not recover but they worked? Sorry, I don't follow you. I think we need to start from the beginning.

 

Check all the instrument panel gauges to make sure they have +12v and solid ground.

 

So you got home with zero oil pressure on the gauge, but 8 blocks from home everything was good. How can everything be good if you have no oil pressure?

I still can't figure out what you are trying to say. What is currently NOT working?

 

Great, so we have something to work with here.... kinda... I just can't figure out why your tachometer is still working. If your tachometer is still working, it can't be a power issue.

If your tacho is NOT working, then I would look at fuse 24. That can affect all the gauges you mentioned, and the suspension system.

A long time ago, someone had an issue with fuse 24 blowing (instrument fuse). The suspension Vertical Accelerometer (behind the front bumper) has a "mass" (block of metal) which broke free inside the accelerometer and was shorting out the internal circuitry of the accelerometer (and blowing fuse 24). The rectangular block is shown in the following photo:

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I'm not sure what holds it in place, but it can be knocked free with a violent jolt (such as you described).

I suppose if it was a partial short, it might not blow the fuse, but drag down the voltage affecting most of the devices attached to fuse 24?

 

If you suspect a short, you can isolate the vertical accelerometer circuit (for faultfinding purposes), but it involves pulling a plug on the back of the relay panel in the frunk.

It's labelled plug "B".


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Obviously you can't drive with that plug disconnected, but you may want to think about trying to de-pin the plug to make your car driveable. The suspension light will remain on, but the suspension will just default to SPORT, I imagine.

Is your HVAC working? Fuse 24 also affects that.

 

Good grief Grant. You never seem to have easy problem to solve.

Nevertheless, if it were my car, I would pull the instrument panel and focus on one non-working gauge. The back of the instrument module has 3 or 5 connectors so they don't all have one 12V pin. Find something easy to deal with like a Tachometer.

Find its power pin, see what wire that is on the connector, trace that back to the power panel, and see why there is no voltage. Or ground.

 

+355

I was going to suggest disconnecting one item at a time to see if the other gauges come good, but then I realised fuse 24 powers about 25 different things.

Oil Pressure Gauge
Fuel quantity processor (in the footwell)
Air bag light
Seat belt light
Suspension fault light
Sport light
Low fuel Light
Oil Pressure Light
Low traction Light
Brake warning Light
F1 AUTO Light
Speedo
F1 display
Water Temperature Gauge
HVAC Hot water recirc pump
Fan speed controller
Blower fan relay coil
AC compressor relay coil
HVAC ECU
Cabin temperature sensor suction fan
Roof switches (on spider)
Roof Controller internal circuits (on spider)
Bilstein Suspension ECU
Suspension Vertical Accelerometer

If your suspension fault light is on, then that means the fuse hasn't blown completely, but something may be dragging down the voltage... or the relay panel has a broken solder connection (and is causing high resistance).

Maybe check the voltage on the fuse?

 

Same exact thing happened to me about 6 months ago. Big bump, dash went dead, though car was still running smoothly. I think he means gauges read zero, not that there was actually no revs/oil pressure/gas/etc, just that the gauges read zero. In driving, the car would only access 1st and 2nd gear, no higher.

BUT, thanks to the wisdom shared here on FChat, I knew to get the car into 2nd gear at the shift point, then pull both paddles to get neutral, then pull either paddle to get 3rd or 4th, and I could shift normally after that all the way up to 6 or down to 1 (until I came to a stop again, in which case I'd have to repeat this move).

The whole thing turned out to be a 10amp fuse which runs all the gauges. 30 seconds later, car ran normally. Cheapest 355 repair ever.

 

One more point to add-- these cars are probably running 25 year old fuses and relays. All it took for my car to blow a 10amp fuse was to hit a big bump. I made a point to replace all fuses and relays after this event.