Circuit Description
The vehicle speed sensor (VSS) assembly provides vehicle speed information to the powertrain control module (PCM). The VSS assembly 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 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 Running the DTC
| • | No MAP sensor DTCs P0107 or P0108. |
| • | No TP sensor DTCs P0122 or P0123. |
| • | No TFP manual valve position switch 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. |
Conditions for Setting the DTC
The transmission output speed is less than 150 RPM for 2.5 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for setting the DTC are met. |
| • | The PCM commands first gear only. |
| • | The PCM commands maximum line pressure. |
| • | The PCM inhibits TCC engagement. |
| • | The PCM freezes shift adapts from being updated. |
| • | The PCM stores DTC P0502 in PCM history during the second consecutive trip in which the Conditions for setting the DTC are met. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes. |
| • | A scan tool clears the DTC from PCM history. |
| • | The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring. |
| • | The PCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the PCM. |
Diagnostic Aids
| • | Inspect the wiring at the PCM, the VSS connector and all other circuit connecting points for the following conditions: |
| - | A backed out terminal |
| - | A damaged terminal |
| - | Reduced 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. |
| • | 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? | -- | ||
Important:: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM. With the drive wheels rotating, does the scan tool Transmission OSS increase with the drive wheel speed? | -- | Go to Diagnostic Aids | ||
Is the resistance within the specified range? | 976-2354 ohms | |||
4 | Measure the resistance from terminal C2-21 to ground. Is the resistance greater than the specified value? | 50 K ohms | ||
Is the voltage greater than the specified value? | 0.3 V | |||
6 |
Is the resistance within the specified range? | 976-2354 ohms | ||
7 |
Refer to General Electrical Diagnosis in Wiring Systems. Refer to Wiring Repairs in Wiring Systems. Was a short to ground condition found? | -- | Go to Diagnostic Aids | |
8 |
Refer to General Electrical Diagnosis in Wiring Systems. Refer to Wiring Repairs in Wiring Systems. Was an open condition found? | -- | 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 in Engine Controls. Is the replacement complete? | -- | -- | |
11 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK |
