P0091 OBD Error Code: Problem & Solutions

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Is your car engine misfiring and having delayed start up? Is there black smoke emitting from the car exhaust? Is there a sudden drop in the fuel economy? All these are the indications to the OBD Code P0091 being stored and flashed in the Powertrain Control Module (PCM).

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.

What causes problem of Fuel Pressure Regulator 1 Control Circuit Low?

• Fuel pump fault/failure
• Fuel pump relay fault/failure
• PCM faulty
• Electric fuel pressure regulator faulty
• Fuel filter or other parts of the fuel system clogged/restricted
• Damaged wiring such as a short to ground
• Fuel tank low fuel levels

1. Fuel Pump - Damaged fuel pump will affect the fuel delivery system and the internal combustion process. Replace it immediately.
2. Fuel Pressure Sensor - If the sensor the faulty, will not read the air pressure correctly thus affecting the air to fuel ratio. Buy new pressure sensor form us.
3. Fuel Pressure Regulator - Faulty regulators will not be able to determine the duel fuel requirement and hamper the fuel delivery system. Replace the damaged one now!
4. Fuel Injection - The fuel injection system lies at the very heart of the diesel engine. By pressurising and injecting the fuel, the system forces it into air that has been compressed to high pressure in the combustion chamber. The diesel fuel injection system consists of: fuel injection pump - pressurised fuel to high pressure. Replace faulty fuel injectors and parts today.
5. Fuel Filters - A fuel filter is a filter in the fuel line that screens out dirt particles from the fuel, normally made into cartridges containing a filter paper. They are found in most internal combustion engines. Fuel filters serve a vital function in today's modern, tight-tolerance engine fuel systems. Replace old and clogged fuel filters now!
6. Diagnostic Tools - Use professional OBD scan tools to diagnose an OBD code error problem. Buy quality diagnostic tools from us now!

P0091 should be considered severe since excessive fuel pressure may lead to a variety of drivability issues and cause internal engine and catalytic converter damage.

Common Symptoms

• Delayed cold start
• Black smoke emission from the exhaust system
• Reduced fuel efficiency
• Engine misfire and rough idle

• Fuel pressure regulator replacement
• Fuel pump replacement
• Fuel filter replacement
• Faulty fuel injectors or other fuel system related sensors replacement
• Repairing or replacing electrical wiring or connectors
• Faulty fuel pump relay replacement
• Vehicle hood is raised and supported
• Removal of defective fuel pump relay
• Installing new fuel pump relay
• Testing the fuel pressure and codes cleared with a scanner or gauge
• Close the vehicle hood and road tested for proper operation

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A mechanic may start with a good visual inspection of the fuel system and the following components: 

• Fuel tank
• Fuel pump
• Fuel filter
• Lines and hoses
• Electrical wiring
• Electrical connectors
• Sensors
• Injectors 

Check for other problematic parts of your vehicle's fuel system that are not listed here that are specific to your particular vehicle. 

During an inspection, the mechanic will take note of any damages to the system and repair them before proceeding with the diagnosis. 

After performing the visual inspection, the mechanic will perform a fuel pressure test to test the functionality of all fuel system sensors. 

If all the parts are checked for perfect operation, then suspect for faults in the Powertrain Control Module (PCM). Although, this error is rare but faulty components should be repaired or replaced and the system should be reprogrammed for eliminating any error. 

Common Mistakes When Diagnosing The P0091 Code 

A most frequent or common mistake when diagnosing the P0091 code can be replacing the fuel pressure regulator or fuel pump without checking if it is bad or not. 

A trouble code is simply a sensor giving a reading that the Powertrain Control Module sees as out of specification. Sometimes, mechanics will see a trouble code and take that for what is actually wrong with the car. Just because a particular part is mentioned in a trouble code, it does not mean that the part is faulty.