95/96 p38 speedo not working

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C256 Pin-16. Needs an oscilloscope to check it properly, although there are some multimeters on amazon wit ha scope feature for a reasonable price. Never tried one though.

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Should I be getting a pulse on this yellow wire going from the becm to the speedo or steady voltage? I am getting approx 4volts. I would of thought it should be moving as the vehicle speeds up and down.
 
Tom24 said:
Should I be getting a pulse on this yellow wire going from the becm to the speedo or steady voltage? I am getting approx 4volts. I would of thought it should be moving as the vehicle speeds up and down.
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You need a scope to check the speedo signal, it's not a voltage level but a pulse which goes via the BECM.
 
I can see all my wheels speeds on my launch diagnostics, would it be possible to have a bad abs ecu an still see the wheels speeds on the diagnostic computer. Wiring and plugs are all checking out OK. I currently have clocks away for testing to make sure they are not faulty to eliminate a few things
 
Tom24 said:
I can see all my wheels speeds on my launch diagnostics, would it be possible to have a bad abs ecu an still see the wheels speeds on the diagnostic computer. Wiring and plugs are all checking out OK. I currently have clocks away for testing to make sure they are not faulty to eliminate a few things
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It would certainly be possible for the wheel speeds to be seen but for the ECU to not produce the required output for the speedo.
Some diagnostics can actually test the instruments, no idea about what you are using.
 
This is possibly my issue as I have checked the wiring from end to end. Also new becm refurbished to fix previous faults. So down to abs ecu and clocks. I have no abs faults though so I was steered towards clocks but I'm not sure as I would of thought if it was the clocks she would still count the miles but it isn't counting the miles. So I'm back thinking clocks aren't seeing the pulse to make speedo and miles work.
 
Although I did try an ecu out of a different vehicle but it had been sitting for a very long time. The numbers nearly matched all but one number. I am sure its a faulty component and not a wiring issue.
 
Tom24 said:
This is possibly my issue as I have checked the wiring from end to end. Also new becm refurbished to fix previous faults. So down to abs ecu and clocks. I have no abs faults though so I was steered towards clocks but I'm not sure as I would of thought if it was the clocks she would still count the miles but it isn't counting the miles. So I'm back thinking clocks aren't seeing the pulse to make speedo and miles work.
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If there are no pulses, it will not count the miles or operate the speedo.
 
Would any of the early spec abs ecu do the job or would every number have to be the exact same.
 
Tom24 said:
Although I did try an ecu out of a different vehicle but it had been sitting for a very long time. The numbers nearly matched all but one number. I am sure its a faulty component and not a wiring issue.
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The number need to match. There are 3 types and they are matched to the brake modulator.

You need to be moving for the ABS sensors to generate a signal. Not sure if early cars can read the speed in diagnostic mode but later ones do as long as you stay slow enough that the light doesn't go out on the dash.
 
Grrrrrr said:
The number need to match. There are 3 types and they are matched to the brake modulator.

You need to be moving for the ABS sensors to generate a signal. Not sure if early cars can read the speed in diagnostic mode but later ones do as long as you stay slow enough that the light doesn't go out on the dash.
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I don't know about Nanocom, but road speed can be seen with Faultmate on more than one screen and the ABS sensors can also be monitored at normal speeds after the ABS light goes out
 
I have a oscilloscope coming to test the pulse. I can see wheel speeds on my diagnostic computer.
 
Datatek said:
I don't know about Nanocom, but road speed can be seen with Faultmate on more than one screen and the ABS sensors can also be monitored at normal speeds after the ABS light goes out
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Don't think that works on Nanocom with WABCO C module. With WABCO D (4W TC) it is supposed to be possible to get a trace with the Nanocom but only as long as it is in diagnostic mode which is something like below 10 kph.

When I get a chance I will fire up my old PC. I took traces of everything I could with the Nanocom at one stage. I've never played with a WABCO D module though. I know some of the Nanocom outputs were switched around (wrong sides) because Marty mentioned it but that may have been fixed in later software updates.
 
Grrrrrr said:
Don't think that works on Nanocom with WABCO C module. With WABCO D (4W TC) it is supposed to be possible to get a trace with the Nanocom but only as long as it is in diagnostic mode which is something like below 10 kph.

When I get a chance I will fire up my old PC. I took traces of everything I could with the Nanocom at one stage. I've never played with a WABCO D module though. I know some of the Nanocom outputs were switched around (wrong sides) because Marty mentioned it but that may have been fixed in later software updates.
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Road speed can be seen in the auto box module and I think the EDC. It's a long time since I looked so I need to check. I have only ever played with WABCO D and I have Faultmate not Nanocom.
 
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