Engine Over Speed Condition
This code indicates that the PCM has received a signal from the engine RPM sensor that the engine has (or is currently) exceeding the maximum allowable limit.
Code Set Parameters
Any RPM reading that exceeds a predetermined limit will cause a code to be stored in the PCM and a service engine soon lamp to be illuminated. Some applications will require multiple failure cycles I order to illuminate a service engine soon lamp.
Symptoms can range from none at all to a no start condition. A service engine soon lamp will almost certainly accompany these symptoms and certain models have a built-in engine disabler if engine RPMs become too excessive. Many late model vehicles can be programmed to shut the engine off when a certain RPM Level is exceeded.
Typical causes of engine over speed include aggressive or inexperienced drivers, shorted or open electrical circuitry, or a bad PCM but the former scenarios rarely occur.
This code is almost always caused by driver error. Technicians report that many drivers are hesitant to admit to over revving the engine, especially if the vehicle is within the warranty period.
- The engine is equipped with overspeed sensor (usually a two or three-wire variable resistance sensor) which provides the PCM with data
- The sensor has a voltage wire (typically it is a 5-volt reference signal) and a ground wire
- The PCM uses the reference voltage wire to monitor engine speed
- As engine speed increases, sensor resistance decreases and reference voltage increases
- As engine RPMs increase, sensor resistance climbs higher, driving reference voltage to the PCM down
- The PCM receives input reference voltage readings as variations in engine RPM and reacts accordingly
- If engine speed is excessive, a code is stored and a service engine soon lamp is illuminated.
A scanner or code reader, a digital volt ohmmeter, and access to a manufacturer’s wiring schematic will be necessary to successfully diagnose this code
Begin your diagnosis with a visual inspection of all wiring and connectors
- Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
- Always retest the system after repairs are completed to ensure success.
If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
- This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
- After the codes are cleared, operate the vehicle to see if the code returns
- If the code fails to immediately return, you may have an intermittent condition
- Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made.
Proceed by unplugging the electrical connector from the engine speed sensor and testing for reference voltage
- This is usually 5-volts but consult your manufacturer’s service manual to be sure
- If there is a 5-volt signal present with the ignition turned to the run position, then check the sensor ground wire
- If both the reference signal and the ground signal are present, test the sensor resistance using the manufacturer’s temperature to resistance chart
- Compare your findings to the manufacturer’s specifications and replace the sensor if it fails to comply.
If the sensor and voltage at the sensor are within acceptable specifications, disconnect the PCM electrical connector and test circuit continuity and resistance between the sensor and the PCM
- Repair or replace system circuitry and components as required and retest the system.
Should all system circuitry and sensors check out, suspect a faulty PCM but keep in mind that PCM failure is rare and PCM replacement will require reprogramming.