Fault code P0091 – fuel pressure regulator 1 control circuit low

Fault code P0091 is called “Fuel Pressure Regulator 1 Control Circuit Low” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0091

This diagnostic trouble code (DTC) is a generic code. Error P0091 is considered a generic code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

Fault code P0091 – fuel pressure regulator 1 control circuit low

Stored code P0091 means that the transmission control module (PCM) has detected a low control circuit signal level in electronic fuel pressure regulator #1. This designation is used in systems that include more than one electronic fuel pressure regulator.

The electronic fuel pressure regulator is normally controlled by the PCM. The battery voltage signal and ground signal are used to control the servo motor. Which controls the valve so that the desired fuel pressure level can be at any engine operation.

When voltage is applied to the servo motor of the electronic fuel pressure regulator, the valve opens in small increments and the fuel pressure increases. When the voltage decreases, the servo motor retracts and the valve closes, and fuel pressure decreases accordingly.

The pressure sensor, is usually located on the fuel ramp where the fuel injectors are located. This allows the PCM to monitor the fuel pressure and adjust the pressure regulator voltage accordingly.

The fuel pressure regulator and fuel pressure sensor can be separate components. But more often than not, they are combined into a single housing and have the same electrical connector.

If the actual signal level in the control circuit is lower than the desired signal level calculated by the PCM, fault code P0091 will be stored. The Malfunction Indicator Light (MIL) may also illuminate.

Symptoms of vehicle malfunctions

The main signal that an error P0091 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The “Check engine” control lamp on the control panel will light up (the code will be stored as a fault).
  2. Other related fault codes may also be present.
  3. The engine may start emergency mode and shut down completely.
  4. Floating revolutions, and attempts to stall at idle.
  5. Large loss of power under load.
  6. The engine stalls or fails to start.
  7. Increased fuel consumption.
  8. Decreased fuel pressure.

Fault P0091 is quite serious, as its occurrence may cause problems with the engine and vehicle controllability. Excessive fuel pressure can cause various problems, as well as engine and catalytic converter damage.

Factors that can cause this error code

The error code P0091 can mean that one or more of the following problems have occurred:

  • Fuel pressure sensor is defective.
  • Short circuit in fuel pressure regulator control wiring harness.
  • Fuel pressure regulator malfunction.
  • Sometimes the cause is a faulty PCM module.

How to fix or reset OBD-2 code P0091

Some suggested steps for troubleshooting and fix the error code P0091:

  1. Connect the scan tool to the vehicle’s diagnostic port to retrieve the stored codes.
  2. Clear the error codes from the memory and test-drive the vehicle to find out if code P0091 appears again.
  3. Perform a visual inspection of the wiring and connectors.
  4. Make sure the regulator on the fuel rail is working properly.
  5. Pay attention to the fuel pressure sensor.

Diagnose and repair of problems

When the cause of the error, in this case P0091, lies on the surface and is easy to fix, that’s one thing. But sometimes it happens that the cause is very difficult to find, so let’s go over the most significant places.

High pressure fuel system

Check all the connectors and wiring harnesses. Make sure there are no bent or twisted contacts or corrosion on them. Replace or repair if necessary.

Pay attention to the fuel injector driver (FID). If the driver or fuel injector has been replaced, the FID should run a re-learning program. Which sets it up for the high pressure pump and fuel injectors.

Inspect the system for fuel leaks, also check the oil level. If the oil level is higher than normal and smells like fuel, look for a fuel injector leak. Especially if you also have fuel correction malfunction codes or ignition skips.

If you can’t find any problems with the high-pressure fuel system. But you have other fuel system related trouble codes. Diagnose and correct them before returning to error P0091.

Fuel lines and regulator

Look for physical damage or kinks in the fuel lines that may be causing difficulties in the supply or return line. It may be necessary to remove the fuel filter to determine if it is clogged and needs to be replaced.

Fuel should flow freely in the direction of flow indicated by the arrow on the fuel filter. On some vehicles the filter is located at the inlet of the fuel pump itself, you will need to remove the module. To determine if there is a lot in the tank, which can also restrict the flow of fuel to the pump.

On vehicles equipped with a reverse fuel system, the regulator is usually located on the fuel rail itself. The fuel pressure regulator has a vacuum line that mechanically limits the fuel supply based on the amount of vacuum created by the engine.

Check for damaged or loose vacuum hoses to the regulator. If there is fuel in the vacuum hose, there may be an internal leak in the regulator, resulting in a loss of pressure.

On non-return systems, the fuel pressure regulator may be located inside the gas tank on the fuel pump module, and the fuel pump module assembly may need to be replaced.

Fuel pressure sensor

Check the fuel pressure sensor by removing the connector and checking the resistance at the terminals using a voltmeter. Resistance should be within factory specifications. Check the reference voltage to the fuel pressure sensor, it should be about 5 volts, depending on the vehicle.

If the voltage is not within specifications, inspect the wiring to determine if there is excessive resistance in the wire. It should be very low, close to 0 ohms. If resistance is present, a ground fault may have occurred and the wiring will need to be traced to locate the fault.

By checking these points, you should be able to determine the problem with error P0091. Once determined, it shouldn’t be too difficult to solve.

On which vehicles does this problem occur most frequently

Fault code P0091 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Alfa Romeo (159)
  • BMW
  • Buick
  • Chevrolet
  • Chrysler
  • Citroen (C4)
  • Dodge
  • Fiat (Ducato)
  • Ford (Fiesta, Transit)
  • GMC
  • Honda
  • Hyundai (Santa Fe, Sonata, Starex)
  • Isuzu
  • Iveco (Daily)
  • Kia (Ceed, Sorento)
  • Mazda (CX-7)
  • Mercedes-Benz (Sprinter)
  • Peugeot (307)
  • Toyota
  • Volkswagen
  • Volvo

Fault code P0091 can sometimes be found with other errors. The most common are the following: P0087, P0088, P0089, P0090, P0092, P0094, P0190, P0191, P0192, P0193, P0194.

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