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Question -
I have a 1996 cavalier with speedo inop. Vehicle speed does show on OTC scanner correctly. Radio was changed to a factory gm radio. I need to know what type of signal comes from PCM to speedo, radio and chime module or why speedo doesn't work. Have 3 differnt heads same problem. Car was wrecked at one time. Green and white wire has continuity and no short to ground or power. Any other ideas?
Answer -
DIGITAL or MECHANICAL speedo display ?.
it has electronic analog speedo and odometer does not work
Does the odometer work correctly ?.
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AnswerIf you are getting the VSS circuit signal input to the PCM from the transmission and you have checked BOTH wires that operate the speedometer and odometer circuit and found no open or shorted circuit on either wire going back to the PCM and you tried 3 different speedo heads you should be getting a check engine fault light illumination on the dash.
Did you test the check engine control circuit to be sure that the check engine light CAN detect a fault by disconnecting lets say the cruise control module and the check engine light should illuminate.
Check your cruise control module to see if you have the 5 volt input signal from the PCM.
I checked my schematics and the only other possible fault besides the possibility that someone may have damaged the speedo circuit wires when they installed the radio. Did you examine all the wires in back of the radio for any puncture marks such as if someone poked a hole in one of the wires with a test light.
Do you have your 5 volt reference signal from the PCM to the IP cluster ?.
2 other items you may want to try and find out as I do NOT have a 1996 Chevy electrical schematic in my library.
I do recall that Cadillac used to use the radio signal as part of the RF signal input and if you removed the radio you would loose the speedometer and odometer operation. I do not know if chevy adopted this method or not.
IF chevy adopted this method and I said "IF" then your problem may be with the radio being faulty and or the INCORRECT radio has been re-installed.
Does the radio work correctly ?.
If I had the corect electrical schematic I would e-mail it to you, ut I don't have one for your particular vehicle.
If memory serves you should have a 5 volt reference feed on one of the wires going to the speedo cluster and the other is a PULSED GROUND that is pulsed ON and OFF by the PCM. If you cannot find the 5 volt reference voltage at the IP cluster and your sure that the wires from the IP cluster back to the PCM are OK, Then I would suspect that you lost the 5 volt reference from the PCM and would need to replace the PCM.
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