P0091 Fuel Pressure Regulator 1 Control Circuit Low
OBD-II Trouble Code Technical Description
Fuel Pressure Regulator 1 Control Circuit Low
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles (Isuzu, Mazda, Dodge, Chrysler, Ford, GMC, Chevy, Toyota, Honda, etc.). Although generic, the specific repair steps may vary depending on make/model.
When a code P0091 is stored, it means that the powertrain control module (PCM) has detected a low voltage signal from the control circuit of the electronic fuel pressure regulator designated 1. The numeral designation 1 is used in systems which have multiple electronic fuel pressure regulators. It may refer to a particular engine bank but not always.
Typically, the electronic fuel pressure regulator is controlled by the PCM. Battery voltage and ground signals are used to control a servo motor which positions the regulator valve so that the desired level of fuel pressure is achieved for any given situation. The fuel pressure sensor is located in the fuel injector rail and allows the PCM to monitor fuel pressure so that it can adjust fuel pressure regulator voltage as necessary. As voltage is increased at the electronic fuel pressure regulator servo motor, the valve is opened and fuel pressure is increased. Decreased voltage at the servo causes it to retract and fuel pressure decreases.
Most often, the fuel pressure regulator and fuel pressure sensor are integrated into a single housing (with one electrical connector) but may be separate components.
If actual fuel pressure regulator control circuit voltage is less than a desired level, as calculated by the PCM, a P0091 will be stored and a malfunction indicator lamp (MIL) may be illuminated.
Related fuel pressure regulator engine codes:
Symptoms & Severity
Since excessive fuel pressure may lead to a variety of drivability issues and cause internal engine and catalytic converter damage, a code P0091 should be considered severe.
Symptoms of a P0091 code may include:
Causes
Potential causes for this code to set are:
Diagnostic and Repair Procedures
In order to diagnose a code P0091, a diagnostic scanner, a digital volt/ohmmeter (DVOM), a suitable fuel pressure gauge, and a reliable vehicle information source (such as All Data DIY) will be required.
NOTE: Extreme caution must be exercised when using a fuel pressure gauge. High pressure fuel contacting hot surfaces or open spark could ignite and cause a fire.
I like to begin with a visual inspection of system wiring and connectors; focusing my attention on harnesses and connectors on top of the engine. The warm upper engine area makes it popular with pests in cold climates. These pests often gnaw system wiring and connectors.
Connect the scanner to the vehicle diagnostic port and retrieve stored codes and freeze frame data. Write this information down as it will prove helpful if the diagnostic process drags on. Clear the codes and test-drive the vehicle if possible.
Should the code be immediately reset, check for the correct degree of voltage and a battery ground at the fuel pressure regulator. If voltage is not discovered, test power supply relays and fuses following the wiring diagram derived from the vehicle information source. If there is no ground, the wiring diagram can help to find the location of the fuel pressure regulator control system ground/s and make sure they are secure.
The presence of voltage and ground at the fuel pressure control regulator would prompt me to obtain fuel pressure specifications from the vehicle information source, then test fuel system pressure using the fuel pressure gauge. Always follow manufacturer’s recommendations for using the fuel pressure gauge. Use the scanner to observe fuel system data while visually monitoring manual fuel pressure with the fuel gauge.
Suspect a faulty fuel pressure sensor if the level of fuel pressure reflected on the scanner does not coincide with actual fuel pressure. Variations in fuel pressure regulator control voltage should mirror fluctuations in actual fuel pressure. If this does not occur, suspect that either the fuel pressure regulator is defective, there is an open or shorted circuit in one of the fuel pressure regulator control circuits, or that the PCM is bad.
Use the DVOM and follow manufacturer’s recommendations for testing the electronic fuel pressure regulator and the individual fuel pressure regulator control circuits. To prevent damage to control modules, disconnect controllers from the circuit before testing circuit resistance and continuity with the DVOM.
Additional diagnostic notes:
Other fuel pressure trouble codes include:
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"Delete Error Code Permanently, Disable DTC Error Code Function for p0091 in the ECU"
In extreme cases, we even have the option to permanently remove the specific DTC p0091 and disable the function of the specific error code in the ECU. All other fault code functions will then continue to work to protect the engine. This is different from clearing an error code with a diagnostic device. We have the option to permanently remove the function of the specific error code, so that it never comes back. Also emergency running that occurs on the specific error code can be solved in most cases.
Of course we prefer to first try to solve the cause of the error code, but sometimes the only solution is to permanently disable the DTC function of p0091.
