Fuel System Leak Detected - Large Leak


The PCM has detected a large leak in the high-pressure area of the fuel system. This code is seen most frequently in diesel applications.

Code Set Parameters

When the PCM detects a sudden decrease in running fuel pressure, this code will be stored and a malfunction indicator lamp may be illuminated. Most models will also enter into a fail-safe or limp-in mode. In this mode engine power will be noticeably reduced and in some instances, the engine will be totally disabled.


This code can come with dramatic symptoms. They may include smoke from the engine area, reduced acceleration, the engine may be disabled, and the strong odor of fuel may be present as well.

Common Causes

Common causes include fuel injector (or injection pump) failure, damaged or defective fuel rail, damaged or burst fuel lines, a fuel pressure sensor malfunction, faulty fuel pressure regulator, clogged fuel filter, leaking injector pump, fuel control actuator failure, fuel temperature sensor failure, fuel heater circuit malfunction (heater on constantly), defective PCM or fuel controller. Open, shorted, damaged, or corroded electrical wiring and connectors may also be the cause of this code.

Common Misdiagnosis

Use caution when working around high-pressure fuel components. Unlike gasoline engines that feature fuel pressure of 35 to 75 psi, diesel engines require extreme amounts of fuel pressure to operate (4,000 to 29,000 psi). Serious injury or even death can result from attempting to diagnose diesel engines without proper knowledge and training.


  • 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 suitable 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, ruptured fuel line/rail, or a problem with the fuel injector/fuel injection pump
  • 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, fuel controller, 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. Start your diagnosis by carefully inspecting the fuel delivery components for leaks
  • If leaks are detected, repair or replace components as required and retest the system to ensure that the repairs corrected the condition that caused this code to be stored
  • If no leaks are detected and fuel pressure is present, continue with the diagnosis. 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.