P0502
DTC P0502 or P0503
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptors
DTC P0502
- Vehicle Speed Sensor Circuit Low Voltage
DTC P0503
- Vehicle Speed Sensor Circuit Intermittent
Diagnostic Fault Information
Typical Scan Tool Data
Circuit/System Description
The vehicle speed sensor (VSS) is mounted on the Transmission and provides the engine control module (ECM) with the vehicle speed signal. The ECM provides a 5 V circuit, a low reference circuit, and a signal circuit to the VSS. The VSS provides a frequency signal that is proportional to an increase in vehicle speed.
Conditions for Running the DTC
P0502
* Ignition voltage is between 11-18 V.
* Engine speed is between 1500-6500 RPM.
P0503
* Ignition voltage is between 11-18 V.
* Engine speed is between 200-7500 RPM for 5 s.
* VSS signal is greater than 200 RPM for 2 s.
* VSS signal change is less than 150 RPM for 2 s.
Conditions for Setting the DTC
P0502
VSS signal is less than 60 RPM for 4.5 seconds.
P0503
VSS signal change is greater than 350 RPM within a calibrated time range.
Action Taken When the DTC Sets
P0502 and P0503 are Type B DTCs.
Conditions for Clearing the DTC
P0502 and P0503 are Type B DTCs.
Diagnostic Aids
The battery must be fully charged. Refer to Battery Inspection/Test Battery Inspection/Test.
Reference Information
Schematic Reference
Manual Transmission Schematics (MR6 (F40)) Electrical Diagrams
Connector End View Reference
* Component Connector End Views Outside Rearview Mirror - Driver
* Inline Harness Connector End Views X100
Description and Operation
Transmission System Description and Operation Transmission System Description and Operation
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References Control Module References for scan tool information
Special Tools
J 35616 - GM-Approved Terminal Test Kit
For equivalent regional tools, refer to Special Tools Tools and Equipment.
Circuit/System Verification
Caution: Refer to Drive Axle Caution Service Precautions.
1. Raise and support the drive wheels in a horizontal position.
2. Start and idle the engine.
3. Place the transmission in second gear and release the clutch pedal.
4. Verify the scan tool VSS parameter increases as the drive wheel speed increases.
• If the VSS does not increase
Refer to Circuit/System Testing.
• If the VSS does increase
5. Operate the vehicle within the conditions for Running the DTC. You may also operate the vehicle within the conditions that you observe from the Freeze Frame/Failure Records data.
6. Verify the DTC does not set.
• If the DTC sets
Refer to Circuit/System Testing.
• If the DTC does not set
7. All OK.
Circuit/System Testing
1. Ignition OFF, and all vehicle systems OFF, disconnect the B14A Transmission Output Shaft Speed Sensor harness connector. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 5 ohms between the low reference circuit terminal 2 and the negative post of the battery.
• If 5 ohms or greater
1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
2. Test for less than 2 ohms in the low reference circuit, wire end to wire end.
• If 2 ohms or greater, repair the open/high resistance in the wire circuit.
• If less than 2 ohms, replace the K20 Engine Control Module.
• If less than 5 ohms
3. Ignition ON.
4. Test for 4.8-5.2 V between the 5 V reference circuit terminal 1 and ground.
• If less than 4.8 V
1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
2. Test for infinite resistance between the 5 V reference circuit and ground.
• If less than infinite resistance, repair the short to ground on the wire circuit.
• If infinite resistance.
3. Test for less than 2 ohms in the 5 V reference circuit, wire end to wire end.
• If 2 ohms or greater, repair the open/high resistance in the wire circuit.
• If less than 2 ohms, replace the K20 Engine Control Module.
• If greater than 5.2 V
1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module. Ignition ON.
2. Test for less than 1 V between the 5 V reference circuit and ground.
• If 1 V or greater, repair the short to voltage on the wire circuit.
• If less than 1 V, replace the K20 Engine Control Module.
• If between 4.8-5.2 V
5. Ignition OFF, connect the test leads of the J 38522 - vehicle signal generator as follows:
* Red test lead to the signal circuit terminal 3 at the B14A Transmission Output Shaft Speed Sensor wire harness connector.
* Black test lead to ground at the transmission case.
* Double black power and ground lead wire to B+ and ground.
6. Set and adjust the J 38522 - vehicle signal generator to the following switch positions:
* Signal switch to 5 V.
* Frequency switch to 60 Hz.
* Duty cycle switch to 50 percent or normal position.
7. Ignition ON.
8. Verify the scan tool vehicle speed sensor parameter displays between 50-70 km/h (31-44 mph).
• If not between 50-70 km/h (31-44 mph)
1. Test for less than 2 ohms in the signal circuit, wire end to wire end.
• If 2 ohms or greater, repair the open/high resistance in the wire circuit.
• If less than 2 ohms, replace the K20 Engine Control Module.
• If between 50-70 km/h (31-44 mph)
9. Replace the B14A Transmission Output Shaft Speed Sensor.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
Control Module References Control Module References for ECM replacement, programming and setup