Injection Pump Timing Offset
The PCM has detected an abnormality in the injection pump timing offset position signal. This type of code pertains exclusively to diesel powered vehicles. If this code is exhibited in a vehicle that is not powered by a diesel engine, suspect a defective PCM.
Code Set Parameters
If the PCM detects variations in the injection pump timing offset position signal that exceed a predetermined number of degrees, a code will be stored and a service engine soon lamp may be illuminated. The maximum allowable number of degrees of variation may differ between manufacturers, vehicle application, engine sizes/types, and transmission applications.
Injection pump timing is critical to diesel engine operation and conditions which cause this type of code to be stored may prove catastrophic if not immediately addressed. Symptoms will likely include a no start condition but can vary between those that are not detectable at all to engine misfire and spark knock upon acceleration. Fuel mileage may also suffer as a result of the possible conditions associated with this code. Other injection and injection pump codes will usually accompany this code as well.
Professional technicians report that the most common causes of this type of code include a lack of oil pressure. Other possible causes may include a defective injection pump, worn or broken timing gears, a bad injection pump timing sensor, or injector pressure sensor. Faulty, damaged, or corroded wiring and electrical connectors are also contributed with failures of a similar nature. PCM failure is possible but rarely occurs.
Professional technicians report that the injection pump is often condemned in error when this code is presented. Even when the injection pump has failed, it is typically caused by low oil pressure and this issue must be addressed prior to injection pump replacement/timing.
- Diesel powered engines utilize a high pressure injection pump for fuel delivery to individual cylinders
- The pump is fed high pressure oil from the engine and timed to the engine camshaft and crankshaft
- The injection pump must keep time with the engine in order to deliver fuel to the individual cylinders at the precise moment
The PCM utilize electro-magnetic injection pump timing offset position sensors and injector pressure sensors to monitor injection pump timing offset and alert the operator of potential malfunctions
- Typical injection pump timing offset position sensor designs use a reluctor ring or teeth (integrated into a splined shaft) to interrupt the field of the stationary electro-magnetic injection pump timing offset position sensor; creating what is interpreted by the PCM as a square wave form pattern
- These interruptions provide the PCM with the precise injection pump timing offset position
- Engine control systems that use this type of system may allow the engine to start and run, despite a injection pump timing offset position sensor circuit or component failure, but engine performance and fuel economy will likely suffer and catastrophic engine damage may be the result
- Malfunction indicator lamp illumination may not occur until multiple failures are documented in this type of system
- In this type of system the PCM uses injection pump timing offset position to calculate fuel delivery
Several specialty tools will be required to diagnose this code successfully
- They include a scanner, a digital volt/ohmmeter, and possibly an oscilloscope.
Begin 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
- Continue by clearing the code and operating the vehicle to see if it returns
- This will help to determine whether or not the malfunction is intermittent
After the codes are cleared, test drive 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
- In the event of an intermittent condition, you may also utilize the oscilloscope to monitor waveforms created by the distributor, camshaft, and/or crankshaft sensor/s, while looking for glitches or other inconsistencies.
Suspect areas of system circuitry that are contaminated with oil, antifreeze, or power steering fluid that has leaked from the engine
- If wiring with missing or distorted insulation is found, repair or replace it as necessary
- Clear the codes and test drive the vehicle to ensure that the repair has been successful.
If no obvious system wiring problems are discovered, perform a resistance test at the crankshaft, camshaft, injection pump timing offset position sensor, and the injection pump pressure sensor
- Replace sensors as required
- Clear the codes and test drive the vehicle to ensure that the repair has been a successful one.
If the sensors comply with manufacturer's specifications, use the digital volt/ohmmeter to test reference voltage at the sensor connector/s and compare your findings with the manufacturer's specified reference voltage
- If system reference voltage readings are in line with specified values (or if sensor resistance values do not coincide), replace the appropriate sensor
- Clear the codes and test drive the vehicle.
Use caution when checking resistance values in wiring that is connected to the PCM
- For best results, disconnect the electrical connector from the PCM prior to using an ohmmeter on the harness side of the circuit
If all sensors coincide with manufacturer's specifications, disconnect the appropriate injection timing and injection pressure sensors, as well as the electrical connectors for all related controllers
- Perform a continuity and resistance test on all system circuits and repair or replace shorted or open circuits or components as required
- Clear the codes and test drive the vehicle to ensure a successful repair has been completed.
If all system circuitry, connectors, and sensors comply with manufacturer's specifications, visually inspect the injection pump sprocket to ensure that it is timed properly
- Repair or replace defective timing components and pumps as required and check system oil pressure.
If the injection pump offset is (mechanically) within specifications (see manufacturer's service manual) and all system circuitry, connectors, and sensors are within the manufacturer's recommended specifications, suspect a defective PCM or related controller
Remember that PCM failure is possible but very rare and PCM (or controller) replacement will require reprogramming.