Start by checking the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.
The cost to diagnose the P0004 code is 1.0 hour of labor. The auto repair's diagnosis time and labor rates vary by location, vehicle's make and model, and even your engine type. Most auto repair shops charge between $75 and $150 per hour.
This fault code is stored in the engine control module when the system cannot correctly control the fuel pressure. The engine control module uses feedback from the fuel pressure sensor to monitor fuel pressure. The fuel pressure regulator circuit integrity is also monitored to ensure the circuit and component are functioning correctly.
Normally manufacturers will support data parameters for actual and desired fuel pressure.
A number of issues may cause this fault code to be set such as a faulty fuel rail pressure sensor, a mechanical fault with the fuel volume regulator could cause the valve to become stuck. An electrical fault such as an open circuit in the fuel volume regulator on a system with a normally closed valve will also cause this situation. A short circuit on the control wire of a normally open fuel volume regulator will also cause this fault.
A fault in the fuel injector return system will cause the fuel pressure to be lower than expected. This causes fuel from the high-pressure circuit to be leaked back to the low-pressure circuit. A faulty maximum pressure relief valve will also cause this situation.
The high-pressure pump should also be tested to ensure it is capable of delivering the required volume of fuel.
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