Circuit Description
Vehicle speed information is provided to the engine control module (ECM) by the vehicle speed sensor (VSS). The VSS is a permanent magnet generator that is mounted in the transaxle and produces a pulsing voltage whenever vehicle speed is over 5 km/h (3 mph). The alternating current (AC) voltage level and the number of pulses increases with vehicle speed. The ECM converts the pulsing voltage into km/h (mph) and then supplies the necessary signal to the instrument panel for speedometer/odometer operation and to the cruise control module and multi-function alarm module operation. This DTC will detect if vehicle speed is reasonable according to engine RPM and load.
Conditions for Setting the DTC
| • | Vehicle speed is less than 5 km/h (3.1 mph) for Power and Decel test. |
| • | The engine is running. |
| • | Engine coolant temperature (ECT) is greater than 60°C (140°F). |
| • | Ignition voltage is between 11-16 volts. |
| • | Power Test: |
| - | The RPM is between 1,200-4,000. |
| - | The throttle position (TP) sensor is between 25-60 percent. |
| - | Engine load is greater than 60 kPa (8.7 psi). |
| • | Deceleration Test: |
| - | Generator compensated manifold absolute pressure (MAP) is less than 30 kPa (4.4 psi). |
| - | The change in RPM per cycle is less than 50 RPM/cycle. |
| - | The TP sensor is less than or equal to 0.8 percent. |
| - | The RPM is between 1,200-6,000. |
| • | DTCs P0107, P0108, P0117, P0118, P0122, P0123, P0201, P0202, P0203, P0204, P0351, and P0352 are not set. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after 3 consecutive trips with a fail. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
| • | A history DTC is stored. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 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. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for more than 10 seconds. |
Diagnostic Aids
| • | An intermittent problem may be caused by a poor connection, rubbed-through wire insulation, or a wire that is broken inside the insulation. |
| • | The VSS signal circuit should be thoroughly inspected for the following conditions: |
| - | Backed-out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed |
| - | Damaged terminals |
| - | Poor terminal-to-wire connection |
| - | Physical damage to the wiring harness |
| • | Ensure the VSS is correctly tightened with proper torque to the transmission housing. |
| • | Refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The On-Board Diagnostic System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
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The permanent magnet generator only produces a signal if the drive wheels are turning greater than 8 km/h (5 mph). This step determines if DTC P0502 is the result of a hard failure 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 ECM 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 is less than the 1,300 ohms, the VSS high and low circuits are shorted together.
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This measures 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 ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Perform an On-Board Diagnostic System Check. Was the check performed? | -- | Go to Step 2 | ||
Notice: Support the lower control arms in the normal horizontal position in order to avoid damage to the drive axles. Do not operate the vehicle in gear with the wheels hanging down at full travel. Does the scan tool display vehicle speed greater than the specific value? | 0 km/h (0 mph) | Go to Step 3 | Go to Step 4 | |
Does the scan tool display vehicle speed greater than the specific value? | 0 km/h (0 mph) | Go to Step 12 | Go to Step 4 | |
Is the voltage near the specified value? | 10.1 V | Go to Step 5 | Go to Step 7 | |
Using a voltmeter connected to ground, measure the voltage at terminal C of the VSS connector. Is the voltage near the specified value? | 11-14 V | Go to Step 6 | Go to Step 8 | |
Using a ohmmeter connected to ground, measure the voltage at terminal A of the VSS connector. Is the voltage near the specified value? | 400 ohms | Go to Step 10 | Go to Step 9 | |
7 | Inspect the VSS signal circuit for an open or short to ground and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 |
Inspect the ignition circuit for an open and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | -- | |
9 | Inspect the VSS ground circuit for an open and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | -- |
Did you complete the replacement? | -- | Go to Step 12 | -- | |
Did you complete the replacement? | -- | Go to Step 12 | -- | |
12 |
Does the scan tool indicate that this diagnostic has run and passed? | -- | Go to Step 13 | Go to Step 2 |
Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK |
