PACCAR PX-9 CM2350 (2013-17) Fault Code:271 PID:SID 126 SPN:1347 FMI:4 Engine Fuel Pump Pressurizing Assembly 1 Circuit – Voltage Below Normal or Shorted to Low Source

Reason:
Engine Fuel Pump Pressurizing Assembly 1 Circuit – Voltage Below Normal or Shorted to Low Source. Low signal voltage is detected at the fuel pump actuator circuit.

Effect:
Possible reduced engine performance.

Circuit Description:
The circuit is a pulse-width modulation (PWM) driver in the engine control module (ECM) that controls the fuel pump actuator. The actuator is grounded in the ECM. The actuator is normally open. The PWM duty cycle to the fuel pump actuator depends on the difference between desired rail pressure and sensed rail pressure.

Component Location:
The high-pressure fuel pump is mounted to the gear housing. The fuel pump actuator is mounted on the fuel pump. The fuel pressure sensor is mounted in the high pressure fuel rail. The fuel pressure relief valve is mounted on the high pressure fuel rail.

Conditions for Running the Diagnostics:
This diagnostic runs continuously when the keyswitch is in the ON position or when the engine is running.

Conditions for Setting the Fault Codes:
The Engine Control Module (ECM) detected a short circuit to ground in the fuel pump actuator signal or return circuit

Action Taken When the Fault Code is Active:
1) The ECM illuminates the amber CHECK ENGINE lamp and/or the Malfunction Indicator Lamp (MIL) immediately when the diagnostic runs and fails.
2) Sensed fuel rail pressure will not follow the commanded rail pressure.
3) Exhaust Gas Recirculation (EGR) valve operation will be disabled.
4) Engine torque will be reduced if the engine is operated for an extended period of time with this fault active.

Conditions for Clearing the Fault Code:
1) To validate the repair, perform a key cycle, start the engine and let it idle for 1 minute.
2) The fault code status displayed by INSITE™ electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.
3) The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.
4) For On-Board Diagnostics (OBD) engines, the ECM will extinguish the Malfunction Indicator Lamp (MIL) after three consecutive trips where the diagnostic runs and passes.
5) The Reset All Faults command in INSITE™ electronic service tool can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Shop Talk:
This fault becomes active when the ECM detects a short circuit in the electronic fuel pump actuator circuit. Causes for this fault code are short circuit to ground or low resistance (fuel pump actuator coil is shorted internally) in the circuit for the fuel pump actuator. When excessive current or a short circuit is detected, the ECM driver to the fuel pump actuator is turned off to protect the circuit. It is necessary to cycle the keyswitch OFF and then back ON before the ECM will test again for the cause of the fault code. The ECM driver is enabled at key ON; if the cause is no longer present, the fault code will become inactive and can be cleared. If the fault code is intermittent, look for causes of an intermittent short to ground in the wiring harness or connectors.

Fault Code 2311 can have high counts if the short circuit condition is or was intermittent.

Possible Causes:
1) Inactive fault codes
2) Faulty fuel pump actuator and circuit
3) Faulty ECM