P0001 Trouble code

What the P0001 code means?

- P0001 : "Fuel Volume Regulator Control Circuit - Open".

- The P0001 code is associated with the electrical circuit which connects to your fuel pressure regulator. Is the OBD-II generic code describing an issue with the circuit which runs from your engine computer (ECM) to your fuel pressure regulator on your fuel injection rail on your engine.

- The ECM regulates your fuel pressure from your fuel pump going to your engine through this circuit. When the computer detects a fault in the circuit, it will set a Check Engine Light (MIL). The code will affect fuel economy and possibly damage the engine.

- This code relates to the the electrical system as part of the fuel volume regulator system. Automotive fuel systems consist of many components, the fuel tank, fuel pump, filter, lines, injectors, etc. One component in high pressure fuel systems is a high pressure fuel pump. It's job is to increase the fuel pressure for the very high pressure needed at the fuel rail for the injectors. These high pressure fuel pumps have a low pressure side and high pressure side, and a fuel volume regulator which controls the pressure. For this P0001 code, it refers to an electrical reading that is "open".

- It also may be related to other codes, such as: P0002, P0003, or P0004.


- The common rail system prototype was developed in the late 1960s by Robert Huber of Switzerland and the technology further developed by Dr. Marco Ganser at the Swiss Federal Institute of Technology in Zurich, later of Ganser-Hydromag AG (est.1995) in Oberägeri.

- The first successful usage in a production vehicle began in Japan by the mid-1990s. Dr. Shohei Itoh and Masahiko Miyaki of the Denso Corporation, a Japanese automotive parts manufacturer, developed the common rail fuel system for heavy duty vehicles and turned it into practical use on their ECD-U2 common-rail system mounted on the Hino Ranger truck and sold for general use in 1995. Denso claims the first commercial high pressure common rail system in 1995.

- Modern common rail systems, whilst working on the same principle, are governed by an engine control unit (ECU) which opens each injector electrically rather than mechanically. This was extensively prototyped in the 1990s with collaboration between Magneti Marelli, Centro Ricerche Fiat and Elasis. After research and development by the Fiat Group, the design was acquired by the German company Robert Bosch GmbH for completion of development and refinement for mass-production. In hindsight, the sale appeared to be a strategic error for Fiat, as the new technology proved to be highly profitable. The company had little choice but to sell Bosch a licence, as it was in a poor financial state at the time and lacked the resources to complete development on its own. In 1997 they extended its use for passenger cars. The first passenger car that used the common rail system was the 1997 model Alfa Romeo 156 2.4 JTD, and later on that same year Mercedes-Benz introduced it in their W202 model.

What causes it?

- The fuel volume regulator code may have several causes:

  • Disconnected plug to the fuel regulator.
  • Possible corrosion in the sensor connector.
  • Damage to the sensor wiring to the ECM.
  • Leaking fuel pressure regulator.
  • Damaged fuel pump.
  • The ECM is damaged.

What are the symptoms?

- The P0001 code will produce a Check Engine Light on the instrument panel/dash and will likely affect:

  • The engine’s performance during driving
  • Vehicle won't start. Possible stalling.
  • Engine stops shortly after starting.
  • "Limp mode" enabled and/or lack of power.
  • It may cause the exhaust to show smoke in various colors from black to white
  • Fuel economy will not be efficient

How serious is it?

  • Inefficient fuel economy.
  • Fuel inestability which may damage your engine.
  • Potentially damage your catalytic converters, which is an expensive repair.
  • Prevent you from passing emissions.

How diagnose this code?

- It is properly diagnosed with a scan tool capable of sensor readings. Then read the data from the scan tool to determine when the problem occurred, or if it is still occurring. Clear the code/light and test drive the vehicle while monitoring data to see if it returns.

- Based upon the conditions of the testing, possibly clearing the code and performing a road test, further diagnosis may be required. Diagnosis may require multiple electrical tools such as:

  • An advanced scan tool to read the ECM data values
  • A digital voltage meter with attachments
  • A fuel pressure tester

What repairs can fix it?

- The most common potential steps to repair it are as follows:

  • Check the connection is correctly made as well as the ground.
  • Check there are no other related electronic faults.
  • Check there are no damaged or cut cables.
  • Check there is a correct working voltage in the valve.
  • Check the condition of the fuel filter as well as fuel hoses, which are not bent or cut.
  • Inspect all of the items listed above. (wiring, leaks, etc)
  • Replace the fuel volume control valve (VCV) or otherwise repair if possible. On some models it is not possible to replace this part and the solution is to replace the whole fuel pump.
  • In other cases, the work of this part can be replaced by a non-return valve, thus avoiding the return of fuel to the tank and improving start-up.
  • Replace the component, wiring, or ECM (requires programming) which is faulty.

Common mistakes

- Do not handle the fuel system without waiting 60 seconds to reduce the fuel pressure in the system. In the common rail system there may be a pressure greater than 1000 bar.

- Avoid handling the system with the engine running. High pressure fuel leaks may occur.

- Just replacing the fuel pressure regulator never guarantees a successful repair in resolving your issue. It may be caused by several components as listed above and more.

- Performing a visual inspection and testing the car with a scan tool, and other special equipment listed above, will verify your issue before spending money and time replacing the fuel pressure regulator unnecessarily.

- Electrical signals require evaluation by a scan tool and voltage meter to ensure that the fuel pressure regulator requires replacement or if another problem exists. Additional testing may be required.

Additional information

- It is a very rare failure because it affects wiring and connections. Generally affects the fuel volume control valve (VCV).

Fuel pump - P0001 fault OBD2

- This valve is responsible for modulating the fuel transfer in the system depending on the requirements of the engine. It can be attached to the ramp or to the high pressure pump. If the pressure is too high it opens and returns the fuel to the tank if otherwise the pressure is too low shut the system to increase the pressure. As a general rule, this valve, when failing, is usually in the open position causing all the fuel to return to the tank, so that each time the vehicle stays in a standstill, it fails to start as it must restore adequate supply and pressure

- Any sensor issue may occur all the time or intermittently. Some fault codes may require more time to diagnose. With this particular code, the solution could be simple or require extensive time to diagnose and repair. Depending on your vehicle, it may take several hours to determine the root cause and repair.

- The sensor may be the cause, wiring issues might be burning/rubbing on another engine component from previous repairs, rodents like to chew wires, or you may have a bad ECM. A scan tool inspection is required. Then we will determine where the fault lies. We could clear the fault code/light first, then verify if the Check Engine Light returns, and go from there. It may have been a weird occurrence from bad gas or weather, or a permanent problem.

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