P0191 Fuel Rail Pressure Sensor "A" Circuit Range/Performance
OBD-II Trouble Code Technical Description
Fuel Rail Pressure Sensor "A" Circuit Range/Performance
What does that mean?
This generic powertrain/engine diagnostic trouble code typically applies to most fuel injected engines, both gas and diesel since 2000. The code applies to all manufacturers such as Volvo, Ford, GMC, VW, etc.
This code is strictly concerned about the incoming signal from the fuel rail pressure sensor not matching what is being delivered to the engine. This can be a mechanical or an electrical circuit fault, depending upon vehicle manufacturer, fuel type and fuel system.
Troubleshooting steps may vary depending upon manufacturer, type of fuel rail pressure system, and type of fuel rail pressure sensor and wire colors.
Symptoms
Symptoms of a P0191 engine code may include:
Malfunction Indicator Lamp (MIL) illuminated Lack of power Engine cranks but won't startCauses
Potential causes for this code to set are:
High fuel pressure Low fuel pressure Damaged FRP sensor Excessive resistance in the circuit Vacuum leaks Low or no fuelDiagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known issue with a known fix put out by the manufacturer and can save you time and money during diagnosis.
Also, with this particular code, make sure you have no fuel pump/fuel pressure related codes. If you have any other codes that point to a fuel pump related issue, diagnose that code first and disregard the P0191 code. Especially when it comes to a no-start related issue.
Next, locate Fuel Rail Pressure Sensor on your particular vehicle. It may look similar to this one:
Once located, visually inspect the connectors and wiring. Look for chafing, rubbing, bare wires, burn spots or melted plastic. Pull the connectors apart and carefully inspect the terminals (the metal parts) inside the connectors. See if they look corroded, burnt or possibly green in color versus the normal metal color you are probably used to seeing. You can get some Electrical Contact cleaner at any parts store if cleaning of the terminals is needed. If this is not possible, find some 91% rubbing alcohol and a light plastic bristle brush to clean them with. Afterwards let them air dry, get some dielectric silicone compound (same stuff they use for light bulb sockets and spark plug wires) and put some where the terminals come into contact.
Next, make sure that the vacuum hose that connects the sensor to the intake manifold is not leaking (if used). Visually inspect all vacuum hose connections at the fuel rail pressure sensor and intake manifold. Replace as needed.
If you have a scan tool, clear the diagnostic trouble codes from memory, and see if this code returns. If it does not, then the connections were most likely your problem.
If the code does return, we will need to test the sensor against a mechanical gauge. First turn the key off, then hook up the fuel pressure gauge. Next connect the scan tool and monitor fuel pressure on the scan tool. Turn the key on and note the pressure on the gauge versus what the scan tool reads. The scan tool and the gauge should be within 5 psi of each other.
If all tests have passed so far, and you continue to get a P0191 code, the last thing to check is the connections at the PCM. Pull the connectors apart and carefully inspect the terminals (the metal parts) inside the connectors. See if they look corroded, burnt or possibly green in color versus the normal metal color you are probably used to seeing.
If all tests have passed and you still get a code P0191, this would most likely indicate a failed PCM. A hard reset (battery disconnect) would recommended before any PCM replaceme
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