Originally Posted by JimBlake
If your check-engine light is on, READ THE ERROR CODE. Why would you want to guess about it when the ECU knows how to store & display that error code?
The ECU looks for the signal from the VSS, & it WILL set the CEL if the signal isn't good. But it's always possible that the VSS itself is good, & the circuit to the ECU is good, but the circuit to the cluster is bad. Or some other combination... The CEL error code says which system isn't right, but the ECU can't tell the difference between a bad VSS or a broken wire. Reading the error code is only the beginning of figuring this out.
I disagree, I've seen from experience VSS's that were bad and never caused a Mil light to come on. Never caused a DTC to store...I seen on a factory scan tool in the data list no speed signal. The VSS isn't high up on the inputs needed for engine operation. See my previous post