Fuel Press Reg 2 Ctrl Circ Low
The PCM has detected an abnormal fuel pressure reading that what is required for normal engine operation. This type of code is limited to vehicles which utilize multiple fuel pressure regulators and may indicate either a lean or rich condition.
Code Set Parameters
When fuel pressure is not within a predetermined range (as determined by the vehicle manufacturer), a trouble code will be stored and a service engine soon lamp may be illuminated. Some models require multiple failure cycles in order for a service engine soon lamp to be illuminated and others will illuminate the service engine soon lamp on the initial failure.
Symptoms typically include a no start condition, extended cranking before engine starts, hesitation upon acceleration, and decreased fuel mileage, along with a stored trouble code and malfunction indicator lamp illumination. Other codes will also likely accompany this type of code including engine misfire codes, lean and/or rich exhaust codes, and mass airflow sensor codes.
Probable causes include a defective electronic fuel pressure regulator, a faulty fuel pump, clogged fuel filter, a low fuel condition, a faulty fuel pump driver/relay, or a defective fuel rail sensor. Open, shorted, damaged, or corroded electrical wiring and/or electrical connectors are also common causes of this code being stored. Wildlife damage (to system circuitry and components) is common on this area of the engine.
Often the fuel pressure regulator is replaced in error when the fuel rail sensor is defective. Techs report that many fuel pumps and other components have been replaced when a vehicle is simply out of fuel. If the fuel level gauge is not working properly, the likelihood of this misdiagnosis becomes more prominent.
- The electronic fuel pressure regulator is used to maintain consistent fuel pressure across the fuel rail, or a section thereof
- Power is supplied to the regulator by the PCM (or fuel delivery module in conjunction with the PCM) and fuel pressure is monitored by the PCM via the fuel rail pressure sensor
- As the fuel rail pressure sensor inputs data to the PCM, voltage variations (from the PCM output to the electronically controlled fuel pressure regulator) command the fuel pressure regulator to restrict or allow fuel as required
- Other input signals from various engine sensors are also used by the PCM to develop a fuel delivery strategy
- As voltage from the PCM is increased, the fuel pressure regulator actuator allows pressure from the fuel pump to build and as voltage (from the PCM) is decreased, fuel pressure is restricted
Several tools will be instrumental in successfully diagnosing this code
- A suitable OBD-II scanner (or code reader), a digital volt/ohmmeter, and a fuel pressure gauge will be most helpful in performing a successful diagnosis
Begin with a visual inspection of all wiring and connectors
- Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
- 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
- Make sure that the engine is filled to the proper level with suitable engine oil.
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.
Connect the fuel pressure gauge to the appropriate location according to manufacturer’s recommendations and turn the key to the ON position
- Observe fuel pressure and compare your actual findings with manufacturer’s specifications found in the service manual
- If the fuel pressure is within specs, test drive the vehicle with the gauge connected and visible through the windshield
- Use caution when working with high pressure fuel lines and fittings
- If the fuel pressure maintains a level that is within the manufacturer’s specifications, suspect a faulty fuel pressure sensor or PCM.
If fuel pressure is insufficient, there is probably an issue with the fuel pump or fuel filter
- Here are some tips for diagnosing these conditions:
Quick Diagnosis: If the vehicle will start, check freeze frame data to determine the conditions that occurred when the code was set and diagnose the problem accordingly
- If the vehicle will not start, then test for fuel pressure using a fuel pressure gauge
- Compare readings to manufacturer’s specifications
- If it is determined that fuel pressure is low, check to make sure that there is fuel in the vehicle
- Once it is determined that fuel is actually in the fuel tank, listen for the sound of the electric fuel pump operating
- If the fuel pump can be heard and the vehicle will not start, suspect a clogged fuel filter or a problem with the fuel injector circuitry (including the PCM)
- If the fuel pump cannot be heard, use a rubber mallet to gently tap the bottom of the fuel tank while someone attempts to start the vehicle
- If the vehicle starts while gently whacking the tank, you have a faulty fuel pump (this is the simplest method of testing)
- If the vehicle still fails to start, then test for battery voltage at the fuel pump connector
- If no voltage is present, follow the fuel pump circuit to the fuse panel, fuel pump relay, and/or the PCM.
Detailed Diagnosis: Many vehicles that are equipped with OBD-II systems use a fuel pressure sensor in the fuel injector rail to monitor operating fuel pressure
- The sensor is of a variable pressure to resistance type
- As fuel pressure increases, sensor resistance decreases, allowing system voltage to increase
- When fuel pressure decreases, sensor resistance increases, causing system voltage to decrease
- The PCM reads these variations in system voltage as fuel pressure and reacts accordingly; adjusting fuel injector pulse width, engine timing, and drivability strategy.
You will need a scanner or a code reader and a digital volt ohmmeter to successfully diagnose this code
Begin by unplugging the electrical connector from the fuel rail pressure 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, check the sensor ground wire
- If both the reference signal and the ground signal are present, test the sensor resistance using the manufacturer’s pressure 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.
Disconnect the connector from the affected fuel pressure regulator and use the digital volt/ohmmeter to test the regulator according to the manufacturer’s specifications
- If the fuel pressure regulator fails to comply with the manufacturer’s specs, replace it then clear the codes and test drive the vehicle to make sure that the repair has been completed successfully.
If fuel pressure regulator testing proves that it is within specifications, disconnect the electrical connectors from the regulator and check for reference voltage and a ground signal at the electronic fuel pressure regulator connector
- Next, plug the electrical connector back into the fuel pressure regulator and monitor signal wire voltage with the digital volt ohmmeter
- Compare your findings with manufacturer’s specifications and replace the fuel pressure regulator if signal voltage fails to comply
- Clear codes and test drive to ensure an effective repair.
If the signal input to the PCM proves to be within manufacturer’s specifications and the scanner shows a contradictory reading, disconnect the connector from the fuel pressure regulator, the fuel pressure sensor, and all related control modules
- Perform a continuity and resistance test on all circuits and compare your findings with the manufacturer’s specifications
- Repair or replace system circuitry, connectors and/or components as required and clear the codes
- Test drive the vehicle to guarantee a successful repair.
If all system circuitry complies with manufacturer’s specifications suspect a defective fuel delivery controller or PCM
- Failure of either of these types of controllers is rare and will require reprograming.