Circuit Description
The Vehicle Speed Sensor Assembly (VSS Assy.) provides vehicle speed information to the Powertrain Control Module (PCM). The VSS Assy. is a Permanent Magnet (PM) generator. The PM generator produces a pulsing AC voltage as rotor teeth on the differential ring gear pass through the sensor's magnetic field. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. The output voltage varies from a minimum of 0.5 volts AC at 100 RPM to more than 100 volts at 8000 RPM. The PCM converts the pulsing voltage to vehicle speed. The PCM uses the vehicle speed signal to determine shift timing and Torque Converter Clutch (TCC) scheduling.
If the PCM detects a low vehicle speed when there is a high engine speed in a drive gear range, then DTC P0502 sets. DTC P0502 is a type B DTC.
Conditions for Setting the DTC
DTC P0502 sets if the following conditions occur two consecutive times:
| • | No MAP Sensor DTCs P0107 or P0108. |
| • | No TP Sensor DTCs P0122 or P0123. |
| • | No TFP Val. Position Sw. DTC P1810. |
| • | The transmission is not in Park or Neutral. |
| • | The TP angle is greater than 15%. |
| • | The engine vacuum is 0-105 kPa. |
| • | The engine speed is greater than 3000 RPM. |
| • | The engine torque is 30-400 lb ft. |
| • | The transmission output speed is less than 150 RPM. |
| • | All conditions met for 2.5 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the Malfunction Indicator Lamp (MIL). |
| • | The PCM commands second gear only, below 2500 RPM. |
| • | The PCM commands maximum line pressure. |
| • | The PCM inhibits TCC engagement. |
| • | The PCM freezes shift adapts from being updated. |
| • | DTC P0502 stores in PCM history. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL after three consecutive trips without a failure reported. |
| • | A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported. |
| • | The PCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the PCM. |
Diagnostic Aids
| • | Inspect the wiring at the PCM, the Vehicle Speed Sensor (VSS) connector and all other circuit connecting points for the following conditions: |
| - | A bent terminal |
| - | A backed out terminal |
| - | A damaged terminal |
| - | Poor terminal tension |
| - | A chafed wire |
| - | A broken wire inside the insulation |
| - | Moisture intrusion |
| - | Corrosion |
| • | When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change. |
| • | Test circuits 400 and 401 for Electromagnetic Interferences (EMI) induced by a wiring harness incorrectly routed too near the spark plug wires. |
| • | Inspect the rotor teeth on the differential ring gear for damage. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Disable the traction control system when performing this step. When the ignition key is cycled to the OFF position and then cycled back ON, the traction control system defaults to ON.
-
This step tests the VSS circuit.
-
This step tests the integrity of the VSS assembly.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls | |
Important:: Before clearing the DTC(s), use the scan tool in order to record the Freeze Frame and Failure Records for reference. Using the Clear Info function will erase the stored Freeze Frame and Failure Records from the PCM. With the drive wheels rotating, does the Transmission OSS increase with the drive wheel speed? | -- | Go to Diagnostic Aids | ||
Is the resistance within the specified range? | 1085-2140 ohms | |||
4 | Measure the resistance from terminal C1-7 to ground. Is the resistance greater than the specified value? | 50 K ohms | ||
Is the voltage greater than the specified value? | 0.5 V | |||
6 |
Is the resistance within the specified range? | 1085-2140 ohms | ||
7 |
Did you find a short to ground condition? | -- | Go to Diagnostic Aids | |
8 |
Did you find an open condition? | -- | Go to Diagnostic Aids | |
9 | Replace the VSS Assembly Refer to Vehicle Speed Sensor Replacement. Is the replacement complete? | -- | -- | |
10 | Replace the PCM. Refer to Powertrain Control Module/Throttle Actuator Control Module Replacement . Is the replacement complete? | -- | -- | |
11 | In order to verify your repair, perform the following procedure:
Has the test run and passed? | -- | System OK |
