Code 24 - Vehicle Speed Sensor (VSS)
The ECM supplies and limits current to 12 volts on circuit 437. The Vehicle Speed Sensor (VSS) located near the instrument panel will sense speedometer rotating element and furnish this information to buffer as a "pulsed" signal (2 cable revolutions of 2002 pulses per mile). The buffer assembly will switch circuit 437 to ground for each pulse received. The ECM uses the time between pulses to determine vehicle speed.
Code 24 is set by the following: Circuit 437 voltage is constant. Engine speed between 1500 and 4400 RPM. Park/Neutral switch indicates transmission is in Drive range. Low MAP (high vacuum) indicating engine deceleration. Loss of VSS will affect TCC and IAC.
- This step checks to see if there is a VSS signal to ECM while turning a drive wheel. Normal voltage will vary from less than 3 volts to over 6 volts as wheel is turned slowly. The faster the wheel is turned, the less the variation.
- This step checks for proper voltage from ECM to buffer connection. If voltage output from ECM to buffer is in normal 10-12 volt range, the fault is in buffer connections or buffer. Low voltage indicates a ground or open to, or in the ECM.