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P0091 Severity
Once the vehicle's onboard system no longer detects the issue, most codes will disappear on their own. If your vehicle still has this code, however, it should be properly diagnosed to avoid a more serious problem.
For a proper diagnosis, RepairPal Certified shops have the equipment, tools, and expertise.
Moderate severity codes might not threaten the vehicle's safety or functionality immediately, but you should still get it diagnosed within a reasonable time frame to keep your car running well.
Diesel engines operate off of high fuel pressure. The engine computer (PCM) uses a Fuel Pressure Regulator to control the fuel on the low pressure side (from the fuel tank) to the high pressure injection pump (pressurizes the fuel to the injectors). If the PCM cannot control the fuel pressure regulator, code P0091 will set.
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OBD-II Code Decreased engine performance is defined as a Fuel Pressure Regulator 1 Control Circuit Low
Diesel engines operate off of high fuel pressure. The engine computer (PCM) uses a Fuel Pressure Regulator to control the fuel on the low pressure side (from the fuel tank) to the high pressure injection pump (pressurizes the fuel to the injectors). If the PCM cannot control the fuel pressure regulator, code P0091 will set.