P0501
Diagnostic Chart (Part 1 Of 2):
Diagnostic Chart (Part 2 Of 2):
Refer to Engine Controls Schematics.
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 more than 32 km/h (20 mph).
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 more than the transmission calculated speed by 32 km/h (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
^ A history DTC clears after 40 consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
^ The scan tool Clear Info function was used.
DIAGNOSTIC AIDS
Check the connections at the VSS buffer and the PCM. Refer to Diagnostic Trouble Code (DTC) List/Type in Automatic Transmission 4L80-E if DTC P0722 or DTC P0723 is also set. Testing and Inspection
TEST DESCRIPTION
Numbers below refer to step numbers on the diagnostic table:
3. Tests for B+ at VSS buffer.
4. Tests for proper ground path for VSS signal buffer.
17. Ensures that the replacement PCM, which utilizes an electrically Erasable Programmable Read Only Memory (EEPROM), is programmed when installed.