Code 42 - VSS - Vehicle Speed Sensor

[dbekk]

I have a 1991 Camry DX with 166K and Code 42 is displayed. My speedometer is working and so is my cruise control. I do have a problem with the engine reving up and down when I take my foot off the accelerator. The RPM rise and fall until I stop moving.

Short of buying a new VSS does anyone have any troubleshooting advise?

Thank you in advance.

[71Corolla]

The speedo in these cars is strictly mechanical, so if the VSS fails the speedo/odo will still work. I'm surprised your cruise control is working . The VSS is simply a reed switch activated by a magnet, so it's possible the reed switch is bad. Swapping out the instrument cluster or the speedometer itself will confirm. You can replace just the reed switch if you are comfortable with a soldering gun.

[Doctor J]

I swapped the sensors but this did not help, so I cut the VSS wire near the ENGINE ECU (but not from the transmission ECU). On my 87 camry it does not cause check engine light to come on.

[dbekk]

Dr J

I am guessing your speedometer did not work after you cut the wire, is that correct?

What color wire is the VSS wire?

Thanks you very much!

[Doctor J]

My speedometer works because it is mechanical (driven by cable) the wire I cut near the engine ecu was purple (but I cannot recall location from the top of my head; you need to see the computer pinout). Cutting wire at the speedometer cluster will set a code for transmission ECU and disable the cruise; the computer controlled transmission uses speedometer sensor as a back up, but if this sensor will be disconnected it will set an error code.
Cutting the wire near the engine ecu will put it into "rpm sensitive" not "speed sensitive" deceleration fuel cut/ fuel resume mode eliminating pulses from the sensor signal "noise" ( but the ECU on 91 model may behave differently)
sorry for confusing explanation