Home » GM 6.5 » GM/Detroit 6.5L ENGINE CONTROLS – DTC P0501 Vehicle Speed Sensor (VSS) Circuit Performance

GM/Detroit 6.5L ENGINE CONTROLS – DTC P0501 Vehicle Speed Sensor (VSS) Circuit Performance

Refer to PCM, VSS Buffer, VSS, EBCM.

Circuit Description
The speed sensor circuit consists of a magnetic induction type sensor, a vehicle speed sensor buffer module and wiring. Gear teeth pressed on the output shaft induce an alternating current in the sensor. This signal is transmitted to the buffer. The buffer compensates for various axle ratios and converts the signal into a square wave for use by the speedometer, cruise control, antilock brake and PCM. The buffer sends two different signals to the PCM.

Conditions for Running the DTC
• The PCM performs this DTC diagnostic continuously.
• The vehicle speed greater than 20 mph.
• The four wheel low not selected.

Conditions for Setting the DTC
• The VSS buffer calculated speed is less than half the transmission calculated speed.
• The VSS buffer calculated speed is greater than the transmission calculated speed by 20 mph.

Action Taken When the DTC Sets
• The PCM disallows all cruise contra! inputs.
• 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
• 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 connections at VSS buffer and PCM. Refer to 4L80E Diagnostic Trouble Codes in Transmission 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.


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