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:
P0089 Fuel Pressure Regulator 1 Performance P0090 Fuel Pressure Regulator 1 Control Circuit P0092 Fuel Pressure Regulator 1 Control Circuit HighSymptoms & 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:
Delayed startup when the engine is cool Black smoke from the exhaust system Diminished fuel efficiency Engine misfire codes and idle control codes may also accompany a P0091Causes
Potential causes for this code to set are:
Shorted or open wiring and/or connectors in the fuel pressure regulator control circuit Defective fuel pressure regulator Faulty fuel rail pressure sensor Bad PCM or a PCM programming errorDiagnostic 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.
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