For 1990-2009 cars
Master Electrical Component List
Manual Transmission Schematics
OBD II Symbol Description Notice
Control Module References

### Circuit Description

Vehicle speed information is provided to the powertrain control module (PCM) by the vehicle speed sensor (VSS). The VSS is a permanent magnet generator that is mounted on the transaxle and produces a pulsing voltage when vehicle speed is over 5 km/h (3 mph). The AC voltage amplitude and frequency increases with vehicle speed. The PCM converts the pulsing voltage into km/h (mph). The PCM supplies the necessary signal to the instrument panel for speedometer, odometer operation and to the cruise control and multi-function alarm module.

If the PCM detects no vehicle speed for a specified length of time, while other sensors indicate that the vehicle is moving, DTC P0502 sets. DTC P0502 is a type B DTC.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Voltage

### Conditions for Running the DTC

• | No VSS DTC P0503.

• | The TP sensor angle is 12 percent or more.

• | The engine speed is 2,000-6,000 RPM.

• | No TP sensor codes.

### Conditions for Setting the DTC

The vehicle speed is 5 km/h (3 mph) or less for more than 13 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 disables Cruise Control.

• | The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.

• | 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 after three consecutive ignition cycles in which the diagnostic test runs and passes.

• | A scan tool can clear the MIL/DTC.

• | 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 DTC passes.

### Diagnostic Aids

Ensure the VSS is correctly torqued to the transmission housing.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step tests the ability of the VSS to produce an AC voltage. This step also verifies the integrity of the wiring to the PCM.

2. This step tests the VSS circuit for correct resistance.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.

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.

3. Record the DTC Freeze Frame and Failure Records.
4. Clear the DTC.

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.

5. Raise and support the drive wheels.
6. Start and idle the engine.
7. Place the transmission in 1st gear.
8. Select Vehicle Speed Sensor on the scan tool.

With the drive wheels rotating, does the Vehicle Speed Sensor parameter increase when the wheel speed increases?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3 |

1. Turn OFF the ignition.
2. Disconnect the PCM connector C3.
3. Using the J 35616 GM-approved terminal test kit, connect the DMM between the VSS high signal circuit and the VSS low signal circuit at the PCM C3 connector.
4. Select AC volts.
5. Turn ON the ignition, with the engine OFF.
6. Rotate the right front drive wheel by hand.
7. Observe the DMM display.

Can a voltage greater than the specified value be obtained?

0.5 V AC

Go to Step 14

Go to Step 4

4 |

1. Leave the DMM test leads connected.
2. Measure circuit resistance.

Is the circuit resistance within the specified range?

1,300-3,160 ohms

Go to Step 8

Go to Step 5

5 | Is the circuit resistance greater than the specified value? | 3,160 ohms | Go to Step 11 | Go to Step 6
6 |

1. Leave the DMM test leads connected.
2. Disconnect the VSS connector at the transmission.

Is the circuit resistance less than the specified value?

1,300 ohms

Go to Step 7

Go to Step 13

7 | Test the high signal circuit and the low signal circuit of the VSS for being shorted together. Refer to Circuit Testing and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 15 | --
8 | Test the high signal circuit of the VSS for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 9
9 |

1. Connect PCM C3.
2. Select DC volts on the DMM.
3. Using the J 35616 , connect the DMM test leads to the VSS high signal and the VSS low signal circuit of the VSS connector.
4. Turn ON the ignition, with the engine OFF.

Does the DMM display system voltage?

--

Go to Step 10

Go to Step 12

10 | Test the high signal circuit of the VSS for a short to voltage. Refer to Testing for a Short to Voltage and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 15 | --
11 |

1. Test the high signal circuit of the VSS for an open.
2. Test the low signal circuit of the VSS for an open.

Refer to Testing for Continuity and Wiring Repairs.

Did you find and correct a condition?

--

Go to Step 15

Go to Step 13

12 |

1. Remove the VSS. Refer to Vehicle Speed Sensor Replacement .
2. Inspect the VSS and the VSS rotor for the following conditions:

• | VSS damage

• | VSS rotor damage

• | Excessive air gap between the VSS rotor and the VSS

• | Incorrect alignment between the VSS and the VSS rotor

3. Repair any of the above conditions as necessary.

Did you find and correct a condition?

--

Go to Step 15

--

13 | Replace the VSS. Refer to Vehicle Speed Sensor Replacement . Did you complete the replacement? | -- | Go to Step 15 | --
14 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 15 | --
15 | Perform the following procedure in order to verify the repair:

1. Select DTC.
2. Select Clear Info.
3. Operate the vehicle and ensure that the VSS is greater than 250 RPM for 2 seconds.
4. Select Specific DTC.
5. Enter DTC P0502.

Has the test run and passed?

--

Go to Step 16

Go to Step 2

16 | With the scan tool, observe the stored information, capture info and DTC info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK