Fault Codes P1271 Fuel Regulator Circuit Malfunction DESCRIPTION: The ECM controls the internal fuel pressure of the common rail by opening and closing the pressure discharge valve. When sudden deceleration occurs, the internal fuel pressure will temporarily become higher than usual and combustion noise may result. Therefore the ECM will open the valve temporarily to discharge the excess pressure inside the common rail. Also, the pressure discharge valve opens when the ignition switch is turned OFF to allow prompt discharge of the common rail internal pressure.
DTC No. P1271 P1272 DTC Detection Open or short in pressure discharge valve circuit. There is no valve opening confirmation (IJF) signal from EDU to ECM despite the ECM sending valve opening command (PRD) signal after the engine is started. (1 trip detection logic) Pressure discharge valve closed malfunction. Actual pressure decreasing rate deviates from the simulated pressure decreasing rate after the ignition switch is turned OFF. (2 trip detection logic) Trouble Area Open or short in pressure discharge valve circuit Open or short in pressure discharge valve itself EDU ECM Open or short in pressure discharge valve circuit (P1271 is set simultaneously) Pressure discharge valve Supply pump ECM
Actuation Description: 1. P1271 (Open or short in pressure discharge valve circuit): This DTC will be set if there is no valve opening confirmation (IJF) signal sent from the EDU to the ECM even though the ECM has commanded the EDU to open the pressure discharge valve. This DTC refers to an open or short circuit malfunction of the pressure discharge valve circuit, not a malfunction that includes a valve that is stuck open or closed. The EDU monitors the current supplied to the pressure discharge valve to verify that the current flows into the valve. If the current exceeds the specified level, the EDU determines that the IJF signal is low. If this DTC is present, the ECM enters the failsafe mode and limits engine power. The fail-safe mode continues until the ignition switch is turned OFF. 1. P1272 (Closed malfunction of the pressure discharge valve): The pressure discharge valve will open and discharge the internal fuel pressure from the common rail to the fuel tank when the ignition switch is turned OFF. When this occurs, the ECM compares the actual drop rate of the internal fuel pressure and the target drop rate. If the ECM judges the actual drop rate is smaller than the target, the ECM then judges that the valve has stuck closed and sets this DTC. This DTC will be stored if the internal fuel pressure does not drop to the target after the ignition switch has been turned OFF. If this DTC is present, the ECM enters a fail-safe mode and limits engine power. The fail-safe mode continues until the ignition switch is turned OFF.
Inspection: 1.READ DTC OUTPUT (DTC P1271 AND/OR P1272) 1. Connect the intelligent tester to the DLC3. 2. Turn the ignition switch ON and turn the tester ON. 3. Enter the following menus: Powertrain / Engine / DTC. 4. Read DTCs. Result: Display (DTC output) Proceed to P1271 and/or P1272 Step 2 P1272 Step 8 2.INSPECT COMMON RAIL ASSEMBLY (PRESSURE DISCHARGE VALVE) 1. Disconnect the P20 pressure discharge valve connector. 2. Measure the resistance of the pressure discharge valve. Standard resistance: Tester Connection 1-2 20 C (68 F) 0.85 to 1.05 Ω If NOT GOOD Replace Discharge Valve Available separately from Baileys Diesel Group If GOOD Go to Step 3
3.CHECK HARNESS AND CONNECTOR (PRESSURE DISCHARGE VALVE - EDU) 1. Disconnect the I14 and I15 EDU connectors. 2. Disconnect the P20 pressure discharge valve connector.
3. Measure the resistance of the wire harness side connector. Standard resistance (Check for open): COM3 (I14-3) - P20-2 Below 1 Ω PRV (I15-3) - P20-1 Below 1 Ω Standard resistance (Check for short): COM3 (I14-3) or P20-2 - Body ground PRV (I15-3) or P20-1 - Body ground 10 kω or higher 10 kω or higher If NOT GOOD, Repair or Replace Harness If GOOD, Go to Step 4
4.CHECK HARNESS AND CONNECTOR (ECM - EDU) 1. Disconnect the I15 and I16 EDU connectors. 2. Disconnect the E8 ECM connector.
3. Measure the resistance of the wire harness side connector. Standard resistance (Check for open): PRD (E8-32) - PRD (I16-5) Below 1 Ω INJF (E8-25) - INJF Below 1 Ω (I15-1) Standard resistance (Check for short): PRD (E8-32) or PRD (I16-5) - Body ground INJF (E8-25) or INJF (I15-1) - Body ground 10 kω or higher 10 kω or higher If NOT GOOD, Repair or Replace Harness If GOOD, go to Step 5
5.INSPECT INJECTOR DRIVER (BATTERY VOLTAGE) 1. Disconnect the I14 and I16 EDU connectors. 2. Turn the ignition switch ON. 3. Measure the voltage of the EDU connectors. Standard voltage: +B (I14-6) - GND (I16-4) 11 to 14 V If NOT GOOD, Check battery > EDU Circuit If GOOD, go to Step 6
6.INSPECT ECM (PRD VOLTAGE) 1. Inspect the ECM using the oscilloscope. 2. Drive the vehicle at 50 km/h (31 mph) in the third gear, and then decelerate by releasing the accelerator pedal. 3. Check the waveform between the terminal of the E7 and E8 ECM connectors. Standard: PRD (E8-32) - E1 (E7-7) Correct waveform shown HINT: Alternative inspection: Run the engine at 2,500 rpm for 10 seconds and then decrease the engine speed to idling by completely releasing the accelerator pedal. If NOT GOOD Replace ECM If GOOD go to Step 7
7.REPLACE INJECTOR DRIVER 1. Replace the injector driver (Click here). Then Clear all Fault Codes and Re-asses if the fault occurs again. 8.REPLACE COMMON RAIL ASSEMBLY (PRESSURE DISCHARGE VALVE) 1. Replace common rail assembly (Click here). Then Clear all Fault Codes and Re-asses if the fault occurs again.