Speedometer Problem when cold
Thread Starter
Pro
Joined: Sep 2003
Posts: 634
Likes: 3
From: Spring Hill Tn.
Speedometer Problem when cold
I have an interesting problem and was wondering if anyone has a similar problem or solution. The winter is here and at start up the speedo/odo do not work. As the car warms up the needle bounces and when the car is warm they both function normally. I've cleaned the sensor and socket, but that has not helped. Does cold gear oil some how effect the speedo magnets or sender?
Thanks
Thanks
Rennlist Member
Joined: Mar 2004
Posts: 499
Likes: 4
From: Milwaukee, WI
Going off memory here.........
1. Assuming it lasts a couple of miles before everything is warmed up, check to see if your cruise control works. If cruise works, then the pulse coming from the transaxle is fine.
2. Can't remember if it's in the WSM, but you can access the electrical connector in the spare tire well. Put a VM (set for volts) on the leads while they're still connected, and with the ignition on (engine off), rotate one of the rear wheels (obviously in neutral and with rear jacked up). You should see pulsing of the needle.
3. Assuming you have pulses, you'll have to focus on the IP and wiring on the bulkhead.
Let us know what you find.
1. Assuming it lasts a couple of miles before everything is warmed up, check to see if your cruise control works. If cruise works, then the pulse coming from the transaxle is fine.
2. Can't remember if it's in the WSM, but you can access the electrical connector in the spare tire well. Put a VM (set for volts) on the leads while they're still connected, and with the ignition on (engine off), rotate one of the rear wheels (obviously in neutral and with rear jacked up). You should see pulsing of the needle.
3. Assuming you have pulses, you'll have to focus on the IP and wiring on the bulkhead.
Let us know what you find.
Rennlist Member
Joined: Jun 2005
Posts: 3,261
Likes: 53
From: Park Ridge, IL (near Chicago)
I've recently noticed the same problemin my 84. I disconnected and cleaned the connectors in the spare tire well, and the two white plastic multi-pin connectors under the pod. I used De-oxit by Craig IIRC. So far problem has not recurred but time will tell.
Good luck,
Dave McK.
Good luck,
Dave McK.
Rennlist Member
Joined: Jun 2005
Posts: 3,261
Likes: 53
From: Park Ridge, IL (near Chicago)
I had hopes that my intermitent speedometer function (and odometer) were fixed when I cleaned my 2 pod connectors and the spare tire connector. It was OK for a while then started to be unreliable. My car is 84S USA.
Well, I pulled my pod and really polished all the multipin foil and connectors. I re-cleaned the spare tire well connector. The speedo itself is a 928 Int'l rebuilt unit that worked fine for 500 miles replacing one that worked but was not accurate. (The odometer always seemed to work fine.) I inspected the foil carefully and it looks OK. I pulled the speedometer itself and the pins looked fine too.
I put everything back and no change. No difference when I hit the pod with my hand. It seems to be more likely to work after it is driven for a couple of miles.
I'm guessing my problem is at either end now: the speedo itself or the speed sensor hookup at the transmission. Since the odometer and speedo needle start and stop together, I'm thinking it is a matter of unreliable signal reaching the unit. If it's in the speed sensor, how involved is it to at least inspect and clean the connection and the wiring?
Thanks in advance,
Dave McK.
Well, I pulled my pod and really polished all the multipin foil and connectors. I re-cleaned the spare tire well connector. The speedo itself is a 928 Int'l rebuilt unit that worked fine for 500 miles replacing one that worked but was not accurate. (The odometer always seemed to work fine.) I inspected the foil carefully and it looks OK. I pulled the speedometer itself and the pins looked fine too.
I put everything back and no change. No difference when I hit the pod with my hand. It seems to be more likely to work after it is driven for a couple of miles.
I'm guessing my problem is at either end now: the speedo itself or the speed sensor hookup at the transmission. Since the odometer and speedo needle start and stop together, I'm thinking it is a matter of unreliable signal reaching the unit. If it's in the speed sensor, how involved is it to at least inspect and clean the connection and the wiring?
Thanks in advance,
Dave McK.
Trending Topics
Rennlist Member
Joined: Jan 2004
Posts: 12,620
Likes: 8
From: Boulder Creek, CA
Do you have the WSMs? If so, look in the cruise control troubleshooting section. (they call it a tempostat 
). There is a pin on the cruise brain connector that IIRC is connected along the same wire that leads to the speedo. The procedure in the WSM describes how you can jack the car up and check for pulses on this line. You could also check for pulses at the connector in the tire well, but checking at the CC brain is a relatively easy way to check the circuit closer to the speedo. It is also possible that the cruise brain is futzing with the signal somehow, so try running with it disconnected too. IIRC you should get 6 or 8 pulses per rear axle revolution. Uhhhh.... unless you have ABS... can't remember offhand what year went to using one of the front ABS sensors.
). There is a pin on the cruise brain connector that IIRC is connected along the same wire that leads to the speedo. The procedure in the WSM describes how you can jack the car up and check for pulses on this line. You could also check for pulses at the connector in the tire well, but checking at the CC brain is a relatively easy way to check the circuit closer to the speedo. It is also possible that the cruise brain is futzing with the signal somehow, so try running with it disconnected too. IIRC you should get 6 or 8 pulses per rear axle revolution. Uhhhh.... unless you have ABS... can't remember offhand what year went to using one of the front ABS sensors.
Rennlist Stories
The Best Porsche Posts for Porsche Enthusiasts
Porsche 911 GT3 Artisan Edition Pays Homage to Japanese Culture
Verdad Gallardo
Porsche Reveals Coupe Variant of the Electric Cayenne With a Fresh Look
Verdad Gallardo
10 Porsche Colors That Have More Personality Than Most People
Verdad Gallardo
Guntherwerks' Final Speedster Creation Is the Ultimate Porsche Restomod
Verdad Gallardo
10 Reasons I Hate Going to the Porsche Dealership (& the 1 Reason I Stay)
Joe Kucinski
Porsche Shakes Up The Nürburgring Lap Record Table Once Again
Verdad Gallardo
6 Ways the Porsche 911 GT3 S/C Redefines Performance
Joe Kucinski
10 Wildest Homologation Specials Porsche Ever Sold
Verdad Gallardo
Super Rare RUF BTR III Comes Out of Hibernation, Looking For a New Home
Verdad Gallardo
Rennlist Member
Joined: Jun 2005
Posts: 3,261
Likes: 53
From: Park Ridge, IL (near Chicago)
Thanks Dave for the info on the speed sensor. I have some more data on my problem:
Outside temp 15-20 oF., the cold speedo starts working at almost exactly same distance(2 mi.) and period of warm-up from cold start. As it comes to life the speedo needle starts to quiver then jump and finally hold an indicated speed. If I slap the top of the pod during this wake up procedure it seems to come back to normal almost immediately.
This makes me think it may be the flexible circuit board on the back of the instrument cluster. The 84 foil is no longer available from big 3. On mine there was one rivet that was re-soldered in the past. I was thinking I would heat it up and make sure I have a good joint. I would use a ohmeter to look at resistances too and see if anything else looks funny.
Has anyone had any experience with this flexible circuit board and any advice about troubleshooting it?
On my car I can check the speed impulse signal at T1 and T2 on the fuse panel and I think I'll do that by jacking the car and turning the rear wheel before I pull my pod again. Since hitting the pod at the right time seemed to help restore the speedo function I think it's in the pod connetions area.
Thanks again,
Dave McK.
Outside temp 15-20 oF., the cold speedo starts working at almost exactly same distance(2 mi.) and period of warm-up from cold start. As it comes to life the speedo needle starts to quiver then jump and finally hold an indicated speed. If I slap the top of the pod during this wake up procedure it seems to come back to normal almost immediately.
This makes me think it may be the flexible circuit board on the back of the instrument cluster. The 84 foil is no longer available from big 3. On mine there was one rivet that was re-soldered in the past. I was thinking I would heat it up and make sure I have a good joint. I would use a ohmeter to look at resistances too and see if anything else looks funny.
Has anyone had any experience with this flexible circuit board and any advice about troubleshooting it?
On my car I can check the speed impulse signal at T1 and T2 on the fuse panel and I think I'll do that by jacking the car and turning the rear wheel before I pull my pod again. Since hitting the pod at the right time seemed to help restore the speedo function I think it's in the pod connetions area.
Thanks again,
Dave McK.
Rennlist Member
Joined: Jan 2004
Posts: 12,620
Likes: 8
From: Boulder Creek, CA
Dave, it's sounding like you have a marginal connection in the pod somewhere, as you guessed. The real PITA about problems in such areas is that it might be fine on the bench, but due to torque/stress on the harness when installed it might be flakey. Just be careful when soldering... it's easy to get so focused on a solder joint that you forget about the heat going into the adjacent plastic...
Rennlist Member
Joined: Jun 2005
Posts: 3,261
Likes: 53
From: Park Ridge, IL (near Chicago)
Small victory maybe?
Well today I had my instrument cluster out 3 times. I tried heating and re-soldering one maybe suspicious joint. I saw a resistance drop after this so I thought this might work. No such luck. I then heated and re-soldered two more joints, but no luck either. Dead. No needle response.
I decided to test my speed sensor. 84S remember. I saw the WSM ref. to jacking car and turning wheel, etc. Instead I put a continuity tester between T1 and T2 on the fuse panel. I put car in neutral and pushed it 1 or 2 feet and the tester light went on and off. Tester at least grossly OK.
Back the instruments.
Speedo has four mini electical receptacles which receive four maybe 22ga.pins from the cluster circuit board. These pins are well soldered to a rigid circuit board which is screwed to the back of the speedo and is riveted to the flexible foil. I checked the resistance from pin to rivet and found two of the four were flaky. Fortunately the pins stick through the foil by 2-3mm, so I soldered a small wire from pin to corresponding rivet. I traced continuity to the 14 pin connectors and all was OK. Once more I put everything back. 10 minutes in or out, no problem.
Started car. I noticed immediately that the speedo works in reverse as well as forward (the sensor is only a switch) and that I got a solid needle response for the first time all day. I don't want to jinx myself but this is the first time it's worked without a 2 mile drive/warmup in a long time.
Hope this helps someone else with same problem
Thanks for the input,
Dave McK..
I decided to test my speed sensor. 84S remember. I saw the WSM ref. to jacking car and turning wheel, etc. Instead I put a continuity tester between T1 and T2 on the fuse panel. I put car in neutral and pushed it 1 or 2 feet and the tester light went on and off. Tester at least grossly OK.
Back the instruments.
Speedo has four mini electical receptacles which receive four maybe 22ga.pins from the cluster circuit board. These pins are well soldered to a rigid circuit board which is screwed to the back of the speedo and is riveted to the flexible foil. I checked the resistance from pin to rivet and found two of the four were flaky. Fortunately the pins stick through the foil by 2-3mm, so I soldered a small wire from pin to corresponding rivet. I traced continuity to the 14 pin connectors and all was OK. Once more I put everything back. 10 minutes in or out, no problem.
Started car. I noticed immediately that the speedo works in reverse as well as forward (the sensor is only a switch) and that I got a solid needle response for the first time all day. I don't want to jinx myself but this is the first time it's worked without a 2 mile drive/warmup in a long time.
Hope this helps someone else with same problem
Thanks for the input,
Dave McK..
