Circuit Description
The 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 to the transmission and produces a pulsing voltage. The AC voltage amplitude and frequency increases with vehicle speed. The ECM converts the pulsing voltage into km/h (mph). The ECM supplies the VSS signal to the following components:
| • | The instrument panel for speedometer and odometer operation |
| • | The cruise control module |
| • | The multi-function alarm module |
If the ECM detects no vehicle speed for a calibrated amount of time, this DTC sets.
DTC Descriptor
This diagnostic supports the following DTC:
DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Voltage
Conditions for Running the DTC
| • | DTCs P0106, P0107, P0108, P0115, P0117, P0118, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0217, P0300, P0351, P0352, P0402, P0404, P0405, P0406, and P0488 are not set. |
| • | The engine is running. |
| • | The engine coolant temperature (ECT) is more than 60°C (140°F). |
| • | The ignition 1 voltage is between 11-16 volts. |
| • | The following are additional Conditions for Running for the applicable test: |
Power Test
| - | The engine speed is between 1,200-4,000 RPM. |
| - | The throttle position (TP) sensor is between 25-60 percent. |
| - | The manifold absolute pressure (MAP) is more than 60 kPa. |
Deceleration Test
| - | The MAP is less than 30 kPa. |
| - | The change in engine speed per cycle is less than or equal to 50 RPM/cycle. |
| - | The throttle position (TP) sensor is less than or equal to 0.8 percent. |
| - | The engine speed is between 1,800-6,000. |
| • | DTC P0502 runs continuously when the above conditions are met. |
Conditions for Setting the DTC
The ECM detects that the vehicle speed is less than 5 km/h (3.1 mph) for more than 35 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
| • | An intermittent condition may be caused by a poor connection, rubbed-through wire insulation, or a wire that is broken inside the insulation. |
| • | Ensure the VSS is correctly torqued to the transmission housing. |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||||||
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | 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. Is the vehicle speed more than the specified value? | 0 km/h (0 mph) | Go to Step 3 | Go to Step 4 | |||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||||
4 |
Is the voltage within the specified range? | 9-11 V | Go to Step 5 | Go to Step 7 | ||||||||||
5 | Measure the voltage at the ignition 1 voltage circuit of the VSS with a DMM. Is the voltage within the specified range? | 11-14 V | Go to Step 6 | Go to Step 11 | ||||||||||
6 | Measure the resistance between the ground circuit of the VSS and battery ground with a DMM. Is the resistance less than the specified value? | 5 ohms | Go to Step 8 | Go to Step 12 | ||||||||||
7 | Test the VSS signal circuit for the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 10 | ||||||||||
8 |
Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 9 | ||||||||||
9 | Test for shorted terminals and poor connections at the VSS. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 13 | ||||||||||
10 | Test for shorted terminals and poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14 | ||||||||||
11 | Repair the ignition 1 voltage circuit between the VSS connector and the fuse for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 15 | -- | ||||||||||
12 | Repair the VSS ground circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 15 | -- | ||||||||||
13 | Replace the VSS. Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||||||
14 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||||||
15 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 16 | ||||||||||
16 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||
