P1185 Possible Causes
- Faulty fuel pressure regulator valve (stuck open)
- Faulty rail pressure sensor
- Rail pressure sensor wiring harness is open or short-circuited
- Poor electrical connection in the rail pressure sensor circuit
How to Fix Code P1185?
Start by checking the “Possible Causes” listed above. Visually inspect the corresponding wiring harness and connectors. Look for damaged components and check for broken, bent, pushed out, or corroded connector pins.
Possible Symptoms
- Engine light on (or engine service warning light soon)
P1185 Meaning
As a rail pressure sensor input signal, the Engine Control Module (ECM) of the common rail diesel engine controls the fuel pressure regulator (integrated into the high-pressure pump) to maintain optimal rail pressure based on the engine’s current speed and load.
However, when a problem that causes the rail pressure to deviate from the target value set by the ECM occurs due to mechanical or electronic reasons, the ECM stops the engine and sets the Diagnostic Trouble Code (DTC) by limiting the fuel (stops injector operation) to prevent the engine from being controlled abnormally. “Rail Pressure Monitoring Error” is the DTC that diagnoses 1) the low-pressure fuel supply condition, 2) the mechanical operating conditions of the high-pressure pump, and 3) indirectly based on the RPS output voltage and RPS service. Therefore, repairing this DTC requires mechanics to have a complete understanding of the fuel supply system.