Diagnostic Instructions
DTC Descriptors
DTC P0502: Vehicle Speed Sensor (VSS) Circuit Low Voltage
DTC P0503: Vehicle Speed Sensor (VSS) Circuit Intermittent
Diagnostic Fault Information
Circuit
| Short to Ground
| Open/High Resistance
| Short to Voltage
| Signal Performance
|
VSS High Signal
| P0502, P0503
| P0502, P0503
| P0502, P0503
| P0502, P0503
|
VSS Low Signal
| --
| P0502, P0503
| --
| P0502, P0503
|
Typical Scan Tool Data
Transmission VSS
Circuit
| Short to Ground
| Open/High Resistance
| Short to Voltage
|
Operating Conditions:
Drive vehicle, normal operating temperature
Parameter Normal Range:
100-7,000 RPM
|
Transmission VSS
| 0 RPM
| 0 RPM
| 0 RPM
|
Circuit/System Description
The VSS system is a pulse generator consisting of a speed sensor assembly, located in the case extension, and a toothed VSS reluctor wheel, which is pressed onto the final drive carrier assembly. As the vehicle drives forward, the VSS reluctor wheel rotates.
This rotation produces a variable AC signal in the pick-up coil that is proportional to vehicle speed. The powertrain control module (PCM) uses this signal in order to calculate vehicle speed, shift timing, and gear ratios.
Conditions for Running the DTC
P0502
| • | No ISS DTC P0716 or P0717. |
| • | No MAP DTC P0105, P0106, P0107, P0108, P1106, or P1107. |
| • | Ignition voltage is between 8.0-18.0 volts. |
| • | The transmission is not in PARK or NEUTRAL. |
| • | The engine speed is greater than 500 RPM for 5 seconds and not in fuel cut-off. |
| • | The engine torque is greater than 50 N·m (37 lb ft). |
| • | The calc. throttle position is 12 percent or greater. |
| • | The input shaft speed is greater than 1,500 RPM. |
| • | The torque converter clutch (TCC) slip speed is 0 RPM or greater. |
| • | The transmission fluid temperature (TFT) is 0°C (32°F) or greater. |
P0503
| • | No ISS DTC P0716 or P0717. |
| • | Ignition voltage is between 8.0-18.0 volts. |
| • | The transmission is not in PARK or NEUTRAL. |
| • | The engine speed is greater than 500 RPM for 5 seconds and not in fuel cut-off. |
| • | The engine torque is greater than 50 N·m (37 lb ft). |
| • | The time since the last gear selector range change is 6 seconds or greater. |
| • | The VSS increases 250 RPM or less for 2 seconds. |
Conditions for Setting the DTC
P0502
The vehicle shaft speed is 150 RPM or less for 5 seconds.
P0503
The vehicle shaft speed drops greater than 1,500 RPM for 2 seconds.
Action Taken When the DTC Sets
| • | DTC P0502 and P0503 are type B DTCs. |
| • | The PCM commands maximum line pressure. |
| • | The PCM freezes transmission adaptive functions. |
| • | The PCM calculates vehicle speed based on engine speed and gear ratio. |
Conditions for Clearing the DTC
DTC P0502 and P0503 are type B DTCs.
Diagnostic Aids
| • | DTC P0502 detects a very low vehicle speed signal when the vehicle has a large engine speed in a drive range, constant fault. |
| • | DTC P0503 detects a large unrealistic drop in the vehicle speed signal in a very short period of time, intermittent fault. |
| • | Inspect the VSS, wire harness, connector, and PCM for metallic debris, damage, or misalignment. Ensure the wiring harness is not stretched too tightly or other components are pressing on the connector body. Also inspect for proper clearance to any
other components and wiring. |
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics
Connector End View Reference
Component Connector End Views
Description and Operation Reference
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Special Tools
Circuit/System Verification
- Raise and support the drive wheels.
- Start and idle the engine.
- Place the transmission in DRIVE.
- Monitor Transmission VSS on the scan tool.
- The Transmission VSS on the scan tool should be greater than 70 RPM.
- Increase throttle position. The VSS RPM should steadily increase.
- Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
- Ignition OFF, disconnect the X3 harness connector at the PCM.
Important: When probing a terminal for testing procedures, it is imperative to use the proper test probe from the J 35616-D GM terminal test kit. Prior versions of the J 35616 GM terminal test kit do not contain
the proper probes for testing TCM/ECM/PCM connectors. TCM/ECM/PCM harnesses use 0.64 mm (0.03 in) round terminals. The correct probe for this size terminal is the light blue J 35616-64B probe. ALL PREVIOUS J 35616-64
AND J 35616-64A PROBES SHOULD BE DISCARDED. The 1.00 mm (0.04 in) brown J 35616-6 probe is most widely mistaken for use with 0.64 mm (0.03 in) terminals. Use of the 1.00 mm (0.04 in) brown
probe in a 0.64 mm (0.03 in) terminal will deform the terminal, likely resulting in an intermittent open condition.
- Using the light blue J 35616-64B probes from the J 35616-D GM terminal test kit, test for greater than 10M ohms from the VSS high signal circuit, PCM X3 harness terminal 12, and the VSS low signal circuit,
PCM X3 harness terminal 44, to a good ground.
| ⇒ | If less than the specified value, test the affected circuit for a short to ground. |
- Using the light blue J 35616-64B probes from the J 35616-D GM terminal test kit, test for between 1,650-3,180 ohms between the VSS high signal circuit, PCM X3 harness pin 12, and the VSS low
signal circuit, PCM X3 harness pin 44.
| ⇒ | If greater than the specified range, test the affected circuits for an open/high resistance. If both circuits test normal, replace the VSS. |
| ⇒ | If less than the specified range, test the affected circuits for a shorted together condition. If both circuits test normal, replace the VSS. |
- Using a 5A fused jumper wire and the light blue J 35616-64B probes, test for greater than 10 K ohms between the VSS high signal circuit, PCM X3 harness terminal 12, and all other circuits of PCM X3
except the VSS low signal circuit, PCM X3 harness terminal 44.
| ⇒ | If less than the specified value, the affected circuits are shorted together. |
- Using a 5A fused jumper wire and the light blue J 35616-64B probes, test for greater than 10K ohms between the VSS low signal circuit, PCM X3 harness terminal 44, and all other circuits of PCM X3, except
the VSS high signal circuit, PCM X3 harness terminal 12.
| ⇒ | If less than the specified value, the affected circuits are shorted together. |
- Using the light blue J 35616-64B probes, test the VSS high signal circuit for less than 10 ohms between PCM X3 harness terminal 12 and terminal 2 of the VSS connector.
| ⇒ | If greater than the specified value, repair the open or high resistance in the affected circuit. |
- Using the light blue J 35616-64B probes, test the VSS low signal circuit for less than 10 ohms between PCM X3 harness terminal 44 and terminal 1 of the VSS connector.
| ⇒ | If greater than the specified value, repair the open or high resistance in the affected circuit. |
- If all circuits and connections test normal, replace the PCM.
Component Testing
- Verify the VSS resistance is between 1,650-3,180 ohms.
| ⇒ | If the resistance is not within the specified range, replace the VSS. |
- Using the
J 35616 GM terminal test kit, connect the DMM between the VSS high signal, VSS connector pin B, and the VSS low signal circuits, VSS connector pin A, at the VSS connector. Raise and
support the drive wheels. While rotating the drive wheels by hand, ensure the AC voltage reading on the DMM is greater than 0.4 volt.
| ⇒ | If the AC voltage is not greater than 0.4 volt, replace the VSS. |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
