hardbodypickup

I can't figure this out. I bought the speed sensor that goes in the tranny.. nothing.. changed the speedo, the check engine light is still on ... and it still points to the speed sensor! ... does anyone know if I'm missing anything?. can't get the truck inspected because of this and would really hate to have to junk it

SPEEDO

what is the code?

hardbodypickup

I can't remember the code offhand but it points to speed sensor two

smj999smj

Having a year/engine/drivetrain for your D21 would be helpful. In general, a vehicle speed sensor is an AC voltage generator. It generates approximately 1 volt (AC) for every 10 MPH. Two wires connect it (and carry the signal) to the back of the speedometer cluster. The speedometer head then converts the voltage and transmits the information to the ECM. Ideally, an oscilloscope would be used to test the signal, as it would show the presence of a clean sine wave signal. Since you probably don't have one, a multimeter can be used in the AC voltage function. If you raise the wheels off of the ground, you can run the leads to the VSS (vehicle speed sensor) terminals in its harness plug. As the speed raises, you will see the voltage rise. This method will at least let you know if the VSS is generating a signal. If it is, then reconnect the VSS harness connector to the main harness and pull the instrument cluster. You can now attach the leads to the appropriate screw heads (of the four that attach the speedo head to the back of the cluster/printed circuit). If you have a signal here, you likely have a bad speedo head (if the speedometer is not working). If no signal, you'll have to check the two wires between the head and the VSS for continuity. If the speedometer is working and you are generating a code, still, you may have to do circuit checks between the speedo head and the ECM. Not likely, but possible, is a bad ECM, but you'll have to isolate that as a possibility by doing some testing, first.

hardbodypickup

Thanks for the information I will test tomorrow!! It's a 97 hardbody pickup

hardbodypickup

the sensor in the tranny works fine and so does the speedo head and now the error codes disappeared and have been replaced by exhaust system codes. I was explaining the sensor problem to a nieghbor and he asked if my reverse lights worked. I said no followed by a 'how the hell did you know that'? .. he said there is something with the speed sensor and the reverse lights and a piece of computer hardware/chip/relay near the battery that will cause the speed sensor error. Has any one heard of this?