P0501

Circuit Description
The speed sensor circuit consists of a magnetic induction type sensor, a Vehicle Speed Sensor buffer module and wiring. The magnetic reluctor pressed on the output shaft induces an alternating current in the sensor. The A/C voltage signal is transmitted to the buffer. The buffer compensates for various axle ratios tire sizes and converts the signal into a square wave for use by the speedometer, the cruise control, the antilock brake, and the PCM. The buffer sends the following two different signals to the PCM:
^ A VSS signal
^ An Output Shaft Speed signal for the automatic transmission

Conditions for Running the DTC
^ The vehicle speed is greater than 20 mph.
^ The four wheel low is not selected.

Conditions for Setting the DTC
The VSS buffer calculated speed is less than half of the transmission calculated speed.
or
^ The VSS buffer calculated speed is greater than the transmission calculated speed by 20 mph.
^ All of the conditions must be met for 2 seconds.

Action Taken When the DTC Sets
^ The PCM will not illuminate the Malfunction Indicator Lamp (MIL).
^ The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Failure Records.

Conditions for Clearing the MIL/DTC
^ The PCM will turn the MIL off after three consecutive trips without a fault condition.
^ A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
^ The use of a scan tool.

Diagnostic Aids
Check the connections at the VSS buffer and the PCM. Refer to 4L80-E Diagnostic Trouble Codes if DTC P0722 or DTC P0723 is also set.

Test Description
Number(s) below refer to number(s) on the Diagnostic Table.
3. This tests for B+ at VSS buffer.
4. This tests for proper ground path for Vehicle Speed Sensor signal buffer.