Low Press Fuel Sys Sensor Circ Low
The PCM has detected a fuel pressure reading that does not coincide with what is required for normal engine operation.
Code Set Parameters
If 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 will be illuminated.
Symptoms typically include a no start condition, extended cranking before engine starts, hesitation upon acceleration, as well as stored trouble code and malfunction indicator lamp illumination.
Probable causes include 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.
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.
- Begin your diagnosis by visually inspecting all wiring and connectors
- Look for shorted or burned wiring and replace circuitry and connectors as required
If the system wiring, connectors, and components appear to be in normal working order, connect the scanner to the diagnostic connector and record all stored trouble 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.
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.