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

### Circuit Description

The vehicle speed sensor (VSS) provides vehicle speed information to the powertrain control module (PCM). The VSS is a permanent magnet generator. The VSS produces an AC voltage as rotor teeth on the transmission output shaft 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.

When 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.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Voltage

### Conditions for Running the DTC

• | No transmission fluid pressure (TFP) manual valve position switch DTC P1810, P1815, P1816.

• | No VSS DTC P0503.

• | The engine torque is 65-550 N·m (48-405 lb ft).

• | The TP angle is 10 to 100 percent.

• | The engine speed is 2,850 to 5,000 RPM.

• | The transmission is not in PARK or NEUTRAL.

### Conditions for Setting the DTC

The transmission output speed is less than 100 RPM for 4.5 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 third gear only.

• | The PCM commands maximum line pressure.

• | The PCM inhibits TCC engagement.

• | The PCM freezes transmission adaptive functions from being updated.

• | 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 during the third consecutive trip 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/or the ignition switch is OFF long enough in order to power down the PCM.

### Test Description

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

1. This step tests the VSS circuit.

2. This step tests the integrity of the VSS.

#### DTC P0502

Step | Action | Values | 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 powertrain control module (PCM).

3. Record the DTC Freeze Frame and Failure Records.
4. Clear the DTC.
5. Raise and support the rear axle assembly.
6. Start the engine.
7. Place the transmission in any drive range.

With the drive wheels rotating, does the scan tool Transmission OSS parameter increase with the drive wheel speed?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Using the DMM and the J 35616 GM Terminal Test Kit, measure the resistance between the vehicle speed sensor (VSS) high signal and VSS low signal circuits at the PCM connector.

Refer to Testing for Continuity .

Does the resistance measure within the specified range?

1377-3355 ohms (2WD)

976-2354 ohms (4WD)

Go to Step 4

Go to Step 7

4 |

1. Place the transmission in NEUTRAL.
2. Select AC volts.
3. Prevent one rear wheel from turning.
4. Rotate the other rear wheel by hand, ensuring that the driveshaft is turning.

Does the voltage measure greater than the specified value?

0.5 V

Go to Step 5

Go to Step 12

5 | Measure the resistance from the high signal circuit of the VSS to ground. Refer to Testing for Continuity . Does the resistance measure greater than the specified value? | 50 K ohms | Go to Step 6 | Go to Step 9
6 |

1. Connect the PCM.
2. Disconnect the engine wiring harness from the VSS.
3. Turn ON the ignition, with the engine OFF.
4. Test the high circuit of the VSS for a short to voltage.

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

7 |

1. Disconnect the engine wiring harness from the VSS.
2. Measure the resistance of the VSS.

Does the resistance measure within the specified range?

1377-3355 ohms (2WD)

976-2354 ohms (4WD)

Go to Step 8

Go to Step 13

8 | Was the resistance measured in Step 3 greater than the specified value? | 3355 ohms (2WD) 2354 ohms (4WD) | Go to Step 10 | Go to Step 11
9 | Test the high circuit of the VSS for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | --
10 |

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

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 15

--

11 | Test the high circuit and the low circuit of the VSS for a short together. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | --
12 |

1. Remove the VSS.
2. Inspect the output shaft speed sensor rotor for damage or misalignment.
3. Inspect the case extension bushing for wear.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

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 . 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, so that the transmission output speed 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