P0297 Vehicle Overspeed Condition
OBD-II Trouble Code Technical Description
ASE Certified Technician
Vehicle Overspeed Condition
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code, which means it applies to most OBD-II equipped vehicles including but not limited to Ford, Nissan, Suzuki, Dodge, Chevrolet, Jeep, Subaru, etc. Although generic, the exact repair steps may vary depending on make/model.
When an OBD-II equipped vehicle 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 actual vehicle speed has exceeded the maximum allowable limit.
The PCM, in most production vehicles sold in North America, is programmed to limit actual vehicle speed to 100 mph. When a VSS signal is received that indicates the vehicle has reached this speed, the PCM is programmed to discontinue the fuel injector pulse signal to all cylinders. This causes an immediate loss of momentum and vehicle speed is decreased. Once 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 at such a position as to allow the reluctor ring to pass by it; in close proximity. The reluctor ring is attached to the output shaft of the transmission so that it spins along with it. As the reluctor ring passes by the electromagnetic tip of the VSS, notches and grooves serve to complete and interrupt the circuit rapidly. These circuit manipulations 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 that indicates the vehicle has exceeded the maximum allowable speed, a code P0287 will be stored (on some vehicles) and a malfunction indicator lamp (MIL) may be illuminated. In some cases, multiple failure cycles will be required for a MIL to be illuminated. This code belongs in the P0200-P02FF batch of diagnostic codes.
Code Severity & Symptoms
Depending upon the symptoms exhibited with a Code P0297, it could be considered severe. If shifting abnormalities or transmission control codes accompany the P0297, it should be addressed with urgency.
Symptoms of a P0297 engine code may include:
- Most commonly, no symptoms will accompany a P0297
- Other transmission control codes
- Transmission shifting irregularities
- Antilock Brake System (ABS) codes
Possible causes for this P0297 code may include:
- The vehicle has been operated in excess of the maximum allowable speed
- Defective VSS or VSS reluctor ring
- Mechanical transmission failure
- VSS system circuits shorted to voltage
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.
Allow me to begin by suggesting that you make sure that the vehicle has not been operated above the maximum allowable speed. If the vehicle has been inadvertently operated above the maximum speed, connect the diagnostic scanner to the vehicle diagnostic port and retrieve all stored codes. You will want to write this information down (along with any available freeze frame data) as it can be helpful as your diagnosis unfolds.
Now, simply clear the code and test-drive the vehicle to make sure that it is 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, you know that there is a malfunction. If the PCM enters readiness mode, you are good-to-go. 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. Consult your vehicle information source for specific testing procedures and specifications. Replace the sensor if it fails to comply with 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 not an acceptable reference voltage signal at the VSS connector, use the DVOM to test the corresponding circuit at the PCM connector. If you discover 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 than an open circuit. If there is no ground at the VSS connector, consult your vehicle information source for the location of system grounds and carefully check them with the DVOM. Make repairs as required.
Test VSS System Circuits
If the reference and ground are both present at the VSS connector, test all VSS system circuits. Prior to 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 which do not adhere to manufacturer’s specifications. If all system circuits are in order, suspect a defective PCM.
- PCM failure is rare
- Actual overspeed vehicle operation is the leading cause of a stored code P0297
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