Erratic/Dead Speedometer
11-03-2005, 04:33 AM
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Racer
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Erratic/Dead Speedometer
So I'm driving home from work yesterday and my speedometer starts going nuts on me. At first it would just waver back and forth about 20mph centered around whatever speed I "think" I was going at the time, but by the time I got home it was really just doing its own thing. It seems to react to wildy to throttle inputs, but when while coasting in neutral and your foot is off the gas it registers at or around 0. Not sure if its related or not, but the gas gauge also seems to have developed a tick, although it seems to be occasional and no where near as bad as the speedo. Its been raining here off and on for the past three days and I wonder if this is a bad ground somewhere, bad gauge cluster, or if this is just a bad speed sensor (in the tranny somewhere?).
I did a search, but all I could find was info on the pre 85.5 cars. Some input would be great, the last thing I need is to get pulled over and have to tell a cop that "my speedo doesn't work....".
The car is an 87' 951, w/ aprox 70k miles.
I did a search, but all I could find was info on the pre 85.5 cars. Some input would be great, the last thing I need is to get pulled over and have to tell a cop that "my speedo doesn't work....".
The car is an 87' 951, w/ aprox 70k miles.
11-03-2005, 11:36 AM
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The instrument cluster contacts tend to need cleaning every now and then to maintain normal operation.
I suggest you follow these directions on Pelican parts: http://www.pelicanparts.com/techarti...e_problems.htm
I suggest you follow these directions on Pelican parts: http://www.pelicanparts.com/techarti...e_problems.htm
11-03-2005, 12:44 PM
#4
Drifting
I had the same problem and fixed it by unplugging the speedo sensor at the tranny and cleaning it out with electronic parts cleaner.
The speedo sensor is located on the upper driver's side of the tranny.
The speedo sensor is located on the upper driver's side of the tranny.
11-03-2005, 09:11 PM
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Thanks guys.
After reading the Pelican artilce it looks like I've got dirty contacts seeing as I have the fuel gauge problem too (previously I thought this was just due to how the tank was shaped).
Exactly how bad is tearing apart the dash anyways? I've never removed a steering wheel let alone one that has ABS and the article isn't what I'd call super descriptive.
After reading the Pelican artilce it looks like I've got dirty contacts seeing as I have the fuel gauge problem too (previously I thought this was just due to how the tank was shaped).
Exactly how bad is tearing apart the dash anyways? I've never removed a steering wheel let alone one that has ABS and the article isn't what I'd call super descriptive.
11-03-2005, 10:09 PM
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Originally Posted by formerGMguy
Thanks guys.
After reading the Pelican artilce it looks like I've got dirty contacts seeing as I have the fuel gauge problem too (previously I thought this was just due to how the tank was shaped).
Exactly how bad is tearing apart the dash anyways? I've never removed a steering wheel let alone one that has ABS and the article isn't what I'd call super descriptive.
After reading the Pelican artilce it looks like I've got dirty contacts seeing as I have the fuel gauge problem too (previously I thought this was just due to how the tank was shaped).
Exactly how bad is tearing apart the dash anyways? I've never removed a steering wheel let alone one that has ABS and the article isn't what I'd call super descriptive.
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11-04-2005, 05:03 AM
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Looks like a good maintenance thing to do anyways. My 86 944 has about the same mileage as your turbo, so maybe it's time.
I had an erratic speedo, then it just died. I replaced the speedo sensor, then everything was good.
Do you have an airbag on that 951? Because I've removed my steering wheel a million times, it's not that big a deal.
Hey, I guess this would be a good time to clean the instrument panel reflectors too, eh? Are they actually attached to the cluster itself, or are they on a different part of the dash?
I had an erratic speedo, then it just died. I replaced the speedo sensor, then everything was good.
Do you have an airbag on that 951? Because I've removed my steering wheel a million times, it's not that big a deal.
Hey, I guess this would be a good time to clean the instrument panel reflectors too, eh? Are they actually attached to the cluster itself, or are they on a different part of the dash?
11-04-2005, 11:56 AM
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Originally Posted by Friendan
Looks like a good maintenance thing to do anyways. My 86 944 has about the same mileage as your turbo, so maybe it's time.
I had an erratic speedo, then it just died. I replaced the speedo sensor, then everything was good.
Do you have an airbag on that 951? Because I've removed my steering wheel a million times, it's not that big a deal.
Hey, I guess this would be a good time to clean the instrument panel reflectors too, eh? Are they actually attached to the cluster itself, or are they on a different part of the dash?
I had an erratic speedo, then it just died. I replaced the speedo sensor, then everything was good.
Do you have an airbag on that 951? Because I've removed my steering wheel a million times, it's not that big a deal.
Hey, I guess this would be a good time to clean the instrument panel reflectors too, eh? Are they actually attached to the cluster itself, or are they on a different part of the dash?
11-04-2005, 02:22 PM
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Reflectors what now?
Yeah, my car has an airbag, that why I'm apprehensive to remove the steering wheel. I was looking at the trim surround for the cluster, how exactly does that thing come off? Do I remove the screws in the airvents first?
Yeah, my car has an airbag, that why I'm apprehensive to remove the steering wheel. I was looking at the trim surround for the cluster, how exactly does that thing come off? Do I remove the screws in the airvents first?
11-04-2005, 02:45 PM
#11
Drifting
to get the trim off, there are 3 screws in the vents. 2 on the left, 1 on the right.
There are two underneath the gauges, one on either side of the steering column. There are 3 above the gauges, spaced evenly. From there it is press fit.
The cluster is held in by 4 gold screws. There are 3 ribbon cables on the back that are removed by spreading their plastic arms.
Be careful of the trip reset switch when reassembling, it is held in place by the trim and must be aligned right.
There are two underneath the gauges, one on either side of the steering column. There are 3 above the gauges, spaced evenly. From there it is press fit.
The cluster is held in by 4 gold screws. There are 3 ribbon cables on the back that are removed by spreading their plastic arms.
Be careful of the trip reset switch when reassembling, it is held in place by the trim and must be aligned right.
11-11-2005, 04:27 PM
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Update:
Well, I took apart the dash and was able to fix the sticking temp gauge as well the fuel gauge by simly cleaning the contacts, but no luck on the speedometer.
Since I first posted the speedo has died along with the trip and odometer, so it looks like I'll be replacing the speed sensor.
Thanks again to all those who posted with help.
Well, I took apart the dash and was able to fix the sticking temp gauge as well the fuel gauge by simly cleaning the contacts, but no luck on the speedometer.
Since I first posted the speedo has died along with the trip and odometer, so it looks like I'll be replacing the speed sensor.
Thanks again to all those who posted with help.
04-12-2006, 09:08 PM
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Hello all,
I have an 85 Euro (german) 928S, and the beginning of this story is that, very infrequently, and seemingly related to perioods of disuse (parked in garage during winter), my speedo quit working completely, interspersed with periods of erratic readings. Essentially I drove the car a couple of days anyway (sans speedo) and it went away (last time, a couple months ago).
Enter other info, which I did not relate to this problem until I did some troubleshooting: the cruise control works only occasionally, and of those times, only occasionally does it truly function, and then usually not for long; then it drifts to way slower speeds, or just stops.
Having a set of honest-to-god factory manuals, I read the appropriate section and grudgingly took out the "tempostat control," as they call it, which lives under the center of the dash, and broke out the multi-meter. I completed all of the diagnostics, which were essentially normal, with the exceptions that, on some terminals where I was supposed to read "battery voltage" under certain conditions, instead, I read a half-volt or so less......AND......where it says to measure the resistance between terminals 11 and 12 and move the car slowly back or forward to test the speedometer sensor.
The "correct" observation is that the resistance alternates between infinite and zero. My actual observation was that the resistance alternated between infinite and about 27 ohms.
It would seem, then, that the sensor is, in fact, bad. (No testing procedure is delineated for the "tempostat control.") I'm curious about a few things, having read the previous posts on this thread: 1). In the opinions of those who know something about this, is this a big enough discrepancy to cause the problems with both the cruise control and the spedometer (which has been functioning normally for weeks now)? 2). The values of infinite and and zero resistance suggest a physical, electrical-contact-nature to this sensor device, and I believe I read someone referring to a rotating magnet in a previous post. What is the actual nature of the sensor device? 3). Someone said it was located upper driver's side of tranny - is this in an auto, manual, what year, etc. (believe it or not, after looking in all four volumes of the factory manual, NOWHERE does it tell me where the damned thing is - the only reference to it I saw at all was in transmission section, which terrified me that it might be an internal component. It said, at the beginning of removing tranny, to disconnect the spedometer sensor lead). 4). Pursuant to the last question, how difficult is this item to replace?
Thank you all in advance for your help.
I have an 85 Euro (german) 928S, and the beginning of this story is that, very infrequently, and seemingly related to perioods of disuse (parked in garage during winter), my speedo quit working completely, interspersed with periods of erratic readings. Essentially I drove the car a couple of days anyway (sans speedo) and it went away (last time, a couple months ago).
Enter other info, which I did not relate to this problem until I did some troubleshooting: the cruise control works only occasionally, and of those times, only occasionally does it truly function, and then usually not for long; then it drifts to way slower speeds, or just stops.
Having a set of honest-to-god factory manuals, I read the appropriate section and grudgingly took out the "tempostat control," as they call it, which lives under the center of the dash, and broke out the multi-meter. I completed all of the diagnostics, which were essentially normal, with the exceptions that, on some terminals where I was supposed to read "battery voltage" under certain conditions, instead, I read a half-volt or so less......AND......where it says to measure the resistance between terminals 11 and 12 and move the car slowly back or forward to test the speedometer sensor.
The "correct" observation is that the resistance alternates between infinite and zero. My actual observation was that the resistance alternated between infinite and about 27 ohms.
It would seem, then, that the sensor is, in fact, bad. (No testing procedure is delineated for the "tempostat control.") I'm curious about a few things, having read the previous posts on this thread: 1). In the opinions of those who know something about this, is this a big enough discrepancy to cause the problems with both the cruise control and the spedometer (which has been functioning normally for weeks now)? 2). The values of infinite and and zero resistance suggest a physical, electrical-contact-nature to this sensor device, and I believe I read someone referring to a rotating magnet in a previous post. What is the actual nature of the sensor device? 3). Someone said it was located upper driver's side of tranny - is this in an auto, manual, what year, etc. (believe it or not, after looking in all four volumes of the factory manual, NOWHERE does it tell me where the damned thing is - the only reference to it I saw at all was in transmission section, which terrified me that it might be an internal component. It said, at the beginning of removing tranny, to disconnect the spedometer sensor lead). 4). Pursuant to the last question, how difficult is this item to replace?
Thank you all in advance for your help.