Circuit Description
The vehicle speed sensor (VSS) provides the powertrain control module (PCM) with the vehicle speed information. The VSS is a permanent magnet generator that is mounted in the transmission. The VSS produces a pulsing voltage whenever the vehicle speed is greater than 5 km/h (3 mph). The AC voltage level and the number of pulses increases with the vehicle speed. The PCM then supplies the signal to the instrument panel for the speedometer, the odometer, the electronic transmission (if equipped), and the cruise control operation. The PCM converts the pulsing voltage into mph the technician can use for calculations.
Conditions for Running the DTC
| • | DTCs P0107, P0108, P0122, and P0123 not set. |
| • | Engine speed is between 1,700 and 3,600 RPM. |
| • | Throttle position (TP) is between 0-1 percent. |
| • | Engine vacuum is between 80-70 kPa. |
| • | Above conditions met for 5 seconds. |
Conditions for Setting the DTC
Vehicle speed is less than 3 km/h (2 mph).
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The PCM will record the operating conditions at the time that the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information. |
| • | A history DTC stores. |
Conditions for Clearing the MIL/DTC
| • | The malfunction indicator lamp (MIL) will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm up cycles without a fault. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
| • | A scan tool should indicate vehicle speed whenever the drive wheels are turning more than 5 km/h (3 mph). A DTC P0502 can be falsely set if the engine is braked-torqued in gear. Disregard if the DTC set while the drive wheels are not turning. |
| • | An intermittent problem may be caused by the following conditions: |
| - | A poor connection |
| - | Rubbed through wire insulation |
| - | A broken wire inside the insulation |
| • | Thoroughly inspect the VSS high and low circuits for backed out terminals, broken locks, and for proper routing. |
| • | Refer to Symptoms . |
Test Description
Numbers below refer to the step numbers on the diagnostic table:
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The permanent magnet generator only produces a signal if the drive wheels are turning greater than 5 km/h (3 mph). This step determines if DTC P0502 is the result of a hard malfunction or an intermittent condition.
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Proper engine loads cannot be achieved in a shop environment to properly run the vehicle within the Freeze Frame Data conditions. It will be necessary to drive the vehicle on the road to obtain the proper engine loads.
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This step verifies that the PCM is receiving a signal from the vehicle speed sensor.
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Refer to service bulletin information for the latest calibration update.
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Refer to the latest Techline information for programming procedures.
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A resistance reading that is higher than the specified value indicates that the VSS circuitry is open.
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If the displayed resistance were less than the 1,300 ohms, the VSS high and low circuits are shorted together. If the resistance value are within the specified value, test the VSS high and low circuits for a short to ground.
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This tests the resistance of the VSS if no opens or shorts were found on the VSS high and low circuits.
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The replacement PCM must be programmed and the Crankshaft Position System Variation Learn procedure must be performed.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||
Does the vehicle speed read above the specified value? | 0 mph | |||||||
Does the vehicle speed read above the specified value? | 0 mph | |||||||
Does the AC voltage measure more than or equal to the specified value? | 0.5 V | |||||||
Verify the vehicle has the most current calibration ID number. Does the vehicle have the most current calibration ID? | -- | |||||||
Reprogram the PCM with the latest calibration ID number. Refer to Powertrain Control Module Replacement/Programming . Did you complete the repair? | -- | -- | ||||||
7 | Measure the resistance between the VSS high circuit and VSS low circuit at the PCM connector. Does the resistance measure more than the specified value? | 1,950 ohms | ||||||
Did you find and correct the condition? | -- | |||||||
9 | Did the resistance value measure within or equal to the specified value? | 1,300-1,950 ohms | ||||||
Did you find and correct the condition? | -- | |||||||
Does the resistance measure within the specified value? | 1,300-1,950 ohms | |||||||
12 | Replace the vehicle speed sensor (VSS). Refer to Vehicle Speed Sensor in Manual Transmission or Vehicle Speed Sensor Replacement in Automatic Transmission. Did you complete the replacement? | -- | -- | |||||
|
Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming Replace the PCM. Did you complete the replacement? | -- | -- | ||||||
14 |
Does the DTC reset? | -- | System OK |
