2013 PACCAR MX-13 – P0261 Common rail pump unit 1 – Voltage too low or short circuit to ground on ECU D420 pin A25

Fault code information

1 trip MIL
3 drive cycle recovery
Readiness group – None
Freeze frame type – Comprehensive

Description of component(s)

The internal plunger is actuated via a roller lifter on the camshaft. Each pump has three pump events every two crankshaft revolutions.

Fuel from the fuel gallery can enter the pump plunger area via an internal valve.
A pump event starts when the plunger travels up, the PCI ECU activates the solenoid briefly, and the internal valve closes the opening to the fuel gallery. The internal valve is kept closed hydraulically, and the fuel is pumped to the rail via a check valve in the outlet bore of the pump unit.

The pump event stops when the roller lifter passes the top of the camshaft lobe, causing the plunger to travel downward again. Due to this, the pressure above the plunger decreases and the internal valve opens the opening to the fuel gallery. The check valve in the outlet bore closes and prevents fuel from flowing back from the rail to the plunger area.

The amount of fuel pumped to the rail depends on the duration of the pump event.
The earlier the solenoid is activated by the PCI ECU in the up stroke of the pump plunger, the more (mg/stroke) fuel is pumped to the rail.

Effect on the system:
Rail pressure control.
The rail pressure is closed-loop controlled. A comparison is made between the actual rail pressure and rail pressure demands determined by the ECU. The rail pressure is adjusted by pumping more or less fuel to the rail with the common rail pump units.

Location of component(s)

Diagnostic condition

Please Contact the Engine Support Center

Set condition of fault code

If High side voltage on the injector (before injection) is less than 20% compared to battery voltage.

Reset condition of fault code

This diagnostic runs when the engine is running

Electrical diagram(s)

Technical data

Possible causes

* Faulty wiring
* Faulty connector
* Faulty solenoid valve

Additional information

No additional information available.

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