Technical Description of OBD-II Trouble Code
Condition of Vehicle Overspeed
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to most OBD-II equipped vehicles, including but not limited to Ford, Nissan, Suzuki, Dodge, Chevrolet, Jeep, Subaru, etc. Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
When a vehicle equipped with OBD-II has stored a code P0297, it means that the powertrain control module (PCM) has detected a signal from the vehicle speed sensor (VSS) indicating that the actual vehicle speed has exceeded the maximum allowable limit.
In most production vehicles sold in North America, the PCM is programmed to limit the actual vehicle speed to 100 mph. When a VSS signal is received indicating that the vehicle has reached this speed, the PCM is programmed to stop the fuel injector pulse signal to all cylinders. This results in an immediate loss of momentum and a decrease in vehicle speed. Once the vehicle speed returns to an acceptable level, the injector pulse signal is restored and acceleration is enabled.
Typically, the VSS is an electromagnetic sensor that uses a rotating reluctor ring to complete an input circuit to the PCM. The VSS is mounted in the transmission housing in close proximity to the reluctor ring, which is attached to the output shaft of the transmission. As the reluctor ring passes by the electromagnetic tip of the VSS, circuit manipulations occur that are recognized by the PCM as transmission output speed or vehicle speed.
A typical VSS or vehicle speed sensor:
If the PCM detects a VSS reading indicating that the vehicle has exceeded the maximum allowable speed, a code P0287 may be stored (on some vehicles) and a malfunction indicator lamp (MIL) may illuminate. In some cases, multiple failure cycles may be required for the MIL to illuminate. This code belongs to the P0200-P02FF batch of diagnostic codes.
Code Severity & Symptoms
Depending on the symptoms exhibited with a Code P0297, it could be considered severe. If there are shifting abnormalities or transmission control codes accompanying the P0297, it should be addressed urgently.
Symptoms of a P0297 engine code may include:
Causes
Possible causes for this P0297 code may include:
Diagnostic and Repair Procedures
A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle information source will be among the tools required to diagnose a code P0297.
Let me begin by suggesting that you ensure that the vehicle has not been operated above the maximum allowable speed. If the vehicle has inadvertently been operated above the maximum speed, connect the diagnostic scanner to the vehicle diagnostic port and retrieve all stored codes. It would be helpful to write down this information (along with any available freeze frame data) as it can assist in the diagnosis process.
Now, simply clear the code and test-drive the vehicle to ensure that it does not reset. Operate the vehicle normally until the PCM enters readiness mode or a code is stored. If the code P0297 is stored after being cleared, it indicates a malfunction. If the PCM enters readiness mode, then everything is fine. If the P0297 is reset and there are no other transmission symptoms or codes, suspect a VSS problem.
Test the VSS
Unplug the electrical connector from the VSS and use the DVOM to test the resistance of the sensor itself. Refer to your vehicle information source for specific testing procedures and specifications. Replace the sensor if it fails to comply with the manufacturer’s recommended specs.
Test Reference Voltage and Ground
If the VSS is within specifications, check for reference voltage and a ground at the sensor connector. With the sensor unplugged, use the DVOM to check for an acceptable reference voltage signal (usually 5-volts) and a ground on the appropriate pins. If there is no acceptable reference voltage signal at the VSS connector, use the DVOM to test the corresponding circuit at the PCM connector. If you find an acceptable reference voltage signal at the PCM connector, suspect a defective wire, splice, or connector between the PCM and the VSS. A false overspeed condition is more likely to be caused by a circuit that is shorted to voltage rather than an open circuit. If there is no ground at the VSS connector, refer to your vehicle information source for the location of system grounds and carefully check them with the DVOM. Make any necessary repairs.
Test VSS System Circuits
If both the reference and ground are present at the VSS connector, test all VSS system circuits. Before using the DVOM to test continuity on system circuits, disconnect all related controllers. Test individual system circuits using the DVOM and repair or replace any circuits that do not adhere to the manufacturer’s specifications. If all system circuits are in order, suspect a defective PCM.
