Fix P0191: Mechanic’s solutions that WORKED

The code P0191: Fuel Rail Pressure Sensor Circuit Range/Performance points out a fault in the fuel rail pressure sensor circuit, and it’s most likely caused by a faulty sensor, fuel pump issues, or wiring problems. This sensor is vital for monitoring the fuel pressure delivered to the engine’s fuel injectors.

P0191 quick overview

Meaning	P0191: Fuel Rail Pressure Sensor Circuit Range/Performance
Is it serious?	The P0191 code can be serious as it relates to fuel pressure, which is crucial for proper engine operation and may lead to performance issues or stalling.
Possible causes	– Faulty fuel rail pressure sensor – Issues with the fuel pump or its relay – Clogged fuel filter leading to low pressure – Damaged wiring or poor connections in the sensor circuit – Problems with the vehicle’s powertrain control module (PCM)
How to diagnose?	Check Fuel Pressure: Measure the actual fuel pressure and compare it to the expected values. Inspect Wiring/Connectors: Look for signs of damage or corrosion on the sensor wiring and connectors. Replace Sensor: If the fuel pressure sensor is suspected to be faulty, consider replacing it. Check Fuel Pump: Evaluate the condition and operation of the fuel pump. Scan for Other Codes: Use a scanner to check for additional codes that may indicate related issues.

How to fix P0191 – learn from mechanics

I looked into P0191 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Ford

Vehicle Information:
2000 Ford Taurus LX 3.0L Stall

Issue + Repair History:

• The car had low fuel pressure (17 PSI).
• Replaced the fuel pump with Airtex and OEM pumps; pressure remained low.
• Found fixes indicating a fuel module under the rear seat.
• Grounding the pump’s ground side increased pressure to 70 PSI.
• Installed a new control module, but the issue persisted.

Suggestions to Fix Issue:

• Check the fuel pressure sensor on the fuel rail.
• Compare scan tool readings with the pressure gauge.
• Consider if a failed pump contaminated the fuel system.
• Inspect the filter and consider replacing it.
• Look for wiring issues under the driver’s seat.

Final Fix:

• A bad ground connection in the trunk was discovered.
• Cleaning the corroded connection under the bolt restored proper fuel pressure.

Case #2: Chevrolet

Vehicle Information:
2013 Chevrolet Malibu Eco 2.4L MIL Lamp on

Issue + Repair History:

• Initially towed for engine replacement; used engine installed.
• After installation, MIL with P0191 code appeared.
• Replaced fuel rail sensor and injector harness from the original motor due to frayed wires.
• New P0013 code appeared alongside P0191 after repairs.

Suggestions to Fix Issue:

• Compare desired vs. actual fuel rail pressure.
• Check freeze frame data to replicate conditions causing the code.
• Confirm the health of the High-Pressure Fuel Pump (HPFP).
• Check for a faulty fuel rail pressure sensor, leaking injector, or fuel supply issues.
• Measure exhaust cam position actuator resistance; consider replacing cam solenoids.
• Perform wiring harness wiggle test for possible loose connections.

Final Fix:

• The high-pressure fuel pump was replaced.
• Despite the inability to replicate the issue in the shop, replacing the pump resolved the problem, and the MIL did not reappear.

Case #3: Jaguar

Vehicle Information:
2003 Jaguar X-Type 2.5L MIL Lamp on

Issue + Repair History:

• Came in with P0191 code and low power.
• Low fuel pressure (30psi) noted; replaced fuel pump.
• After replacement, fuel pressure increased to 55psi at idle and 85psi in closed loop.
• Replaced fuel pressure sensor, fuel pump driver module, and PCV hose.

Suggestions to Fix Issue:

• Clear Keep Alive Memory (KAM) by disconnecting the battery.
• Question if an OEM or aftermarket pump was used.
• Monitor the fuel rail pressure sensor closely for dropouts.
• Be suspicious of the fuel pressure sensor’s accuracy.
• Check the commanded fuel pressure duty cycle on the scanner.

Final Fix:

• Resetting the Keep Alive Memory (KAM) resolved the issue.
• Fuel pressure stabilized at 55-60 psi at idle.

Case #4: Chevrolet

Vehicle Information:
2019 Chevrolet Silverado 2500 HD LTZ 6.6L MIL Lamp on

Issue + Repair History:

• Initial P0191 code with no drivability issues.
• Replaced burnt pressure sensor pigtail and sensor.
• Code returned after 500 miles; focused on Fuel Pressure Regulators (FPRs).
• Replaced driver-side fuel rail with attached FPR #2 after erratic adjustments.
• Truck returned after 2485 miles with the same P0191 code.

Suggestions to Fix Issue:

• Check for circuit issues, especially at terminal x112 on top of the engine.
• Perform a drag test on connections and check the circuit end-to-end with a meter.
• Inspect the rear fuel tank for collapsing as per TSB 19-NA-277.

Final Fix:

• No definitive fix was identified at the time of the last update.
• The technician continued to investigate, considering advice to inspect connectors and potential circuit issues.

Case #5: Mazda

Vehicle Information:
2009 Mazda B2300 2.3L No Start, MIL Lamp on

Issue + Repair History:

• Engine light on with P0191 code (“fuel rail pressure”).
• Previously replaced fuel rail pressure sensor and Suction Control Valve (SCV).
• Intermittent no-start and stalling issues.
• Conducted an injector leak-back test with even results.

Suggestions to Fix Issue:

• Possible intermittent fuel pump issue.
• Check for air intake issues, particularly through the hand primer.
• Consider installing a one-way valve to the main intake fuel line to prevent leak-back.

Final Fix:

• Installed a one-way valve in the main intake fuel line to prevent any leak-back.
• The vehicle has not faulted since the installation, though the fix was based on the commonality of air intake issues, not a definitive diagnosis.

Advice	Brief Description of Diagnostic Step
Check Fuel Pressure	Monitor actual vs. desired fuel pressure to identify discrepancies.
Inspect Wiring and Connectors	Examine for burnt, frayed, or loose connections, especially at crucial points like fuel sensors and pigtails.
Replace Fuel Pressure Sensor	If the sensor or its connections are damaged, consider replacing to ensure accurate readings.
Consider Fuel Pump Issues	Investigate the health and operation of the fuel pump, as intermittent issues can lead to P0191.
Look for Air Intake Problems	Check for air sucking, particularly through hand primers or other components, which might cause pressure irregularities.
Reset or Relearn Necessary Systems	Resetting systems like Keep Alive Memory (KAM) or relearning processes might resolve the issue if other repairs have been made.

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