1990 S4 Speedo not working
06-23-2014, 12:31 PM
#1
Thread Starter
1990 S4 Speedo not working
Need some help finding the problem with my speedometer. Neither the gauge or the digital display are working. All other gauges are okay. I will have to check if all the digital 'functions' are working or not.
Where should I start looking?
90 S4 Auto
Where should I start looking?
90 S4 Auto
06-23-2014, 01:13 PM
#2
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check fuse #25
__________________
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
06-23-2014, 07:59 PM
#5
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In theory all 1990 cars are supposed to have their speedometer signal coming from the left front ABS sensor, but apparently Porsche was randomly using up leftover magnetic pickup wheels, old style diff covers, or ????, as some cars have the early magnetic pickup in a round depression in the rear diff cover, while others use the ABS sensor.
Discussion is here:
https://rennlist.com/forums/928-foru...28-owners.html
So I'd start by seeing whether your car has a magnetic pickup on the rear diff cover. It'll look like so, below. If you don't have one, then the issue is elsewhere. Any other warnings on the digidash?
Discussion is here:
https://rennlist.com/forums/928-foru...28-owners.html
So I'd start by seeing whether your car has a magnetic pickup on the rear diff cover. It'll look like so, below. If you don't have one, then the issue is elsewhere. Any other warnings on the digidash?
06-23-2014, 08:06 PM
#6
Rob,
Any idea how to convert from the old style to the new style? I have the old style and I'm going to the corvette trans....
Any idea how to convert from the old style to the new style? I have the old style and I'm going to the corvette trans....
06-23-2014, 08:15 PM
#7
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#25 is the classic fuse failure for the speedo not to work. Did you change the fuse or do a continuity test on it?
Try also #39 & #41 for grins.
Then follow Rob's advice.
Try also #39 & #41 for grins.
Then follow Rob's advice.
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06-23-2014, 08:30 PM
#8
Thread Starter
Rob!
Thank you for your info. I am quite sure there is no magneto. I am fairly intimate with the underbelly of my car but give me a day or so to investigate. I need to finish the fuses and relay clean up. ABS will be the next to investigate as it just stopped working all of the sudden.
Thanks guys!
06-23-2014, 10:11 PM
#9
Thread Starter
For sure no magneto. Cleaned the connections to the abs. Still no speedo. Also no trip or mileage calculator on the digital dash!
More help... I will go through Robs checklist ASAP
06-23-2014, 10:38 PM
#10
Rennlist Member
06-24-2014, 12:42 AM
#11
Thread Starter
Maybe a few of the GTS guys will have an idea as the dash and speedo are similar I think?
The good thing is I have gone through the ce panel and 14 pin without success other than lots of other issues have improved!
I should say that I fixed nothing when it quit. Since, new ignition switch and steering rack...
06-24-2014, 12:54 AM
#12
Thread Starter
In theory all 1990 cars are supposed to have their speedometer signal coming from the left front ABS sensor, but apparently Porsche was randomly using up leftover magnetic pickup wheels, old style diff covers, or ????, as some cars have the early magnetic pickup in a round depression in the rear diff cover, while others use the ABS sensor.
Discussion is here:
https://rennlist.com/forums/928-foru...28-owners.html
So I'd start by seeing whether your car has a magnetic pickup on the rear diff cover. It'll look like so, below. If you don't have one, then the issue is elsewhere. Any other warnings on the digidash?
Discussion is here:
https://rennlist.com/forums/928-foru...28-owners.html
So I'd start by seeing whether your car has a magnetic pickup on the rear diff cover. It'll look like so, below. If you don't have one, then the issue is elsewhere. Any other warnings on the digidash?
No magneto so has to be an ABS issue. Is that on the fender or at the wheel??! TIA
06-24-2014, 01:31 AM
#13
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Could be anywhere along the circuit:
-One of the front ABS sensors (the '92 Service info Tech book mentions that in the 1992 GTS, the speedometer signal comes from the left rear ABS sensor, which is changed from the front sensors in earlier (89-91? 90-91?) cars)
-A dodgy wiring harness from the front ABS sensor connector on the spindle to the inner fender connector - we've all seen pictures of those harnesses having completely shed their insulation.
- Dirty contacts at the ABS brain ('90 has the 55 pin combination ABS/PSD brain, above your left foot) (speedo signal seems to go through it...)
The ABS/PSD brain is hiding behind the mirror memory module here, you can see the 55 pin connector- disconnect battery ground, pivot the bail on the connector, remove connector, and clean it with Deoxit:
This speedometer signal thing is such a freaking mess, it doesn't help that for every year between '88 and '92 there are annual changes to the ABS/PD brain, the ABS wiring harness, the digidash, etc. I have a spare ABS harness from a '91GT, if one of the folks that can actually read a wiring diagram could suss where the front ABS signal feeds into the ABS brain, I could easily figure out which (if not both) front ABS wires feeds the signal.
-One of the front ABS sensors (the '92 Service info Tech book mentions that in the 1992 GTS, the speedometer signal comes from the left rear ABS sensor, which is changed from the front sensors in earlier (89-91? 90-91?) cars)
-A dodgy wiring harness from the front ABS sensor connector on the spindle to the inner fender connector - we've all seen pictures of those harnesses having completely shed their insulation.
- Dirty contacts at the ABS brain ('90 has the 55 pin combination ABS/PSD brain, above your left foot) (speedo signal seems to go through it...)
The ABS/PSD brain is hiding behind the mirror memory module here, you can see the 55 pin connector- disconnect battery ground, pivot the bail on the connector, remove connector, and clean it with Deoxit:
This speedometer signal thing is such a freaking mess, it doesn't help that for every year between '88 and '92 there are annual changes to the ABS/PD brain, the ABS wiring harness, the digidash, etc. I have a spare ABS harness from a '91GT, if one of the folks that can actually read a wiring diagram could suss where the front ABS signal feeds into the ABS brain, I could easily figure out which (if not both) front ABS wires feeds the signal.
06-25-2014, 02:50 PM
#15
Thread Starter
Update. I have something similar to your picture. I have the white magneto with the small spring clip but no wire coming from it as in your picture! My cover is quite different than yours. Maybe because it is an auto as apposed to your GT.
So why no wire leaving the magneto? ABS sensor then?
I confirmed that all functions are working except speedometer and odometer
Any help appreciated!
So why no wire leaving the magneto? ABS sensor then?
I confirmed that all functions are working except speedometer and odometer
Any help appreciated!