Odometer not working any more...

[BigRed80]

Hi guys,

I desperately need your help with my Saleen XP8
I have been having trouble with my odometer for some time now. More specifically, it stopped working and is not showing any movement any more. I also started getting an OBD error code at that time regarding the speed sensor (not sure about the code right now, but I can look it now). I replaced the speed sensor, but that didnt fix the OBD error code nor the faulty odometer. Two days ago I remember that I have a Scangauge OBD thingy which I connected to the OBD port. Interestingly enough, the Scangauge did show a speed reading.

Can anybody explain this behavior? Getting an OBD error code and having the odometer not move made me think that somewhere between the sensor and the computer the sensor wire was damaged and the signal wasnt getting to the computer, which according to my understanding would explain what I was experiencing. But getting a speed reading from the Scangauge would suggest that the signal is indeed getting to the computer, but not getting to the gauge cluster (or the gauge cluster is damaged).

Any ideas?

Thanks for any help

 

[2000StreetRod]

speedometer work?

If your 2000 is like mine the vehicle speed signal is generated by the 4 wheel anti-lock brake system module and sent to the PCM, instrument cluster, speed control servo, radio, GEM, message center and outside air temperature module. Check fuses 25 and 11 in the central junction box. Does your speedometer work? If your speedometer works but not your odometer I think the problem is internal to the instrument cluster.

 

[pbnj22]

and there a pita to remove. my tachometer stopped working ( thinks its just a bad connection on the backside of the cluster) and i was planning on taking out the dash to fix it but after reading some how tos on here i decided to just let it be..

 

[BigRed80]

Thanks for the quick replies.
[MENTION=111113]2000StreetRod[/MENTION]: Neither the speedometer (the speed needle) nor the odometer (mileage counter) work. Sorry, I wasnt clear enough about that. Does the OBD error code come from the PCM? The OBD information I was getting with the Scangauge come from the PCM, right?

 

[2000StreetRod]

PCM controls OBD-II data

Thanks for the quick replies.
[MENTION=111113]2000StreetRod[/MENTION]: Neither the speedometer (the speed needle) nor the odometer (mileage counter) work. Sorry, I wasnt clear enough about that. Does the OBD error code come from the PCM? The OBD information I was getting with the Scangauge come from the PCM, right?

Yes, the PCM reads the various sensors and provides them in digital format to the OBD-II bus. Since the PCM is providing vehicle speed to your Scanguage it must be receiving the data from the 4WABS. You can confirm the 4WABS signal by testing your cruise control. If the cruise control doesn't work then there is a problem with the output of the 4WABS. The PCM monitors engine rpm, vehicle speed and gear ratio selected and compares them. The OBD error may be because the PCM is computing a mismatch between the vehicle speed and the rpm/gear selected. There is no way for the PCM to determine that your analog odometer and speedometer are not working.

 

[BigRed80]

Sounds good, I will check the cruise control first thing in the morning. BTW, the OBD error code I am getting is P0500.
So are you saying that getting the OBD error code and the odometer/speedometer not working are two separate issues? And what exactly do you mean by 4WABS? The speed sensor I replaced was located in the rear axle differential. Is that it?

Sorry for asking stupid questions I really need to get this fixed, car needs to go to inspections very soon...

Thanks again.

 

[2000StreetRod]

Rear axle sensor

The rear axle sensor wires are connected to the 4 wheel anti-lock brake system (4WABS) module under the hood. The rear axle sensor is the original source of the vehicle speed signal which is modified and distributed by the 4WABS to all the other components that need the signal. For example, the VSS is used by the radio to increase the volume as vehicle speed increases to compensate for road noise. I don't have a message center but I think it uses the VSS to compute and display things that are speed dependent.

 

[BigRed80]

Alright, so the speed signal goes from the VSS in the rear axle differential to the 4WABS, then to the PCM and then to the instrument cluster. And since I am getting a speed reading from OBD, the signal seems to go to the PCM alright. But if that is the case, how can the PCM be the source of the OBD error code??

 

[BigRed80]

I found a wiring diagram on ebscohost.com and as far as I am understanding this correctly it says that the signal from the sensor goes first directly to the 4WABS and from the 4WABS to the instrument cluster and to the PCM. Can anyone confirm this?

What I am still not getting is that I am seeing a speed signal on the OBD port which as far as I know is coming from the PCM, but also getting an OBD error code also coming from the PCM?!?! wtf?!?!

 

[2000StreetRod]

Maybe someone else can help

I found a wiring diagram on ebscohost.com and as far as I am understanding this correctly it says that the signal from the sensor goes first directly to the 4WABS and from the 4WABS to the instrument cluster and to the PCM. Can anyone confirm this?

I stated that in previous posts using my 2000 Explorer Wiring Diagrams as a reference. Why do you need someone else to confirm?

What I am still not getting is that I am seeing a speed signal on the OBD port which as far as I know is coming from the PCM, but also getting an OBD error code also coming from the PCM?!?! wtf?!?!

As I previously posted the PCM has more than one way to determine vehicle speed. When two methods do not agree the PCM reports an error which is up to the service technician to resolve.

P0500 Vehicle Speed Sensor Malfunction

The rear axle sensor signal could be bad and the vehicle speed on your Scangauge could be PCM computed using engine rpm, transmission gear, rear axle ratio and tire radius. I wish you luck.

 

[BigRed80]

Sorry, didnt mean to question you. I thought I had understood from you that the signal from the sensor first goes to the PCM and then to the 4WABS, thats why I was surprised to find it the other way around, which is what I wanted to get confirmed, thats all.