What Does P0191 Mean?
This code indicates the fuel rail pressure sensor A circuit is not operating within its expected range or is failing to track properly with commanded fuel pressure changes. The ECM has detected that the sensor output does not match expected values based on engine load, RPM, and fuel pump commands. This suggests the sensor is reading inaccurately or the fuel system has an actual pressure delivery problem.
Common Causes
35%
Faulty fuel rail pressure sensor A providing inaccurate readings due to internal calibration drift or contamination on the sensing diaphragm
25%
Weak or failing fuel pump unable to maintain target fuel rail pressure across operating conditions
20%
Leaking fuel injector(s) causing fuel rail pressure to drop faster than expected during key-off or bleed down faster than the pump can compensate
20%
Restricted fuel filter or supply line reducing fuel volume to the rail and preventing target pressure from being reached
Diagnostic Steps
1
Step 1: Compare the fuel rail pressure sensor PID reading on a scan tool against a known-accurate mechanical fuel pressure gauge installed at the rail test port. A discrepancy greater than 5 PSI indicates sensor inaccuracy.
2
Step 2: Monitor fuel rail pressure at idle, under load (snap throttle), and during key-off. Normal idle pressure is typically 35-65 PSI (port injection) or 500-2000+ PSI (GDI). Pressure should hold within 5 PSI for at least 5 minutes after key-off.
3
Step 3: Check fuel pump volume delivery by disconnecting the supply line at the rail and measuring output into a graduated container. Most systems require at least 750 mL per 30 seconds at full pump speed.
4
Step 4: Inspect the fuel filter for restriction; if it has not been replaced within the maintenance interval, install a new filter and recheck pressure.
5
Step 5: Perform an injector leak-down test by pressurizing the rail with the engine off and monitoring for pressure loss. More than 2 PSI drop per minute suggests a leaking injector.
Estimated Repair Cost
$150 - $600
Parts + labor, varies by vehicle and location
This code indicates the fuel rail pressure sensor A circuit is not operating within its expected range or is failing to track properly with commanded fuel pressure changes. The ECM has detected that the sensor output does not match expected values based on engine load, RPM, and fuel pump commands. T...
The most common cause of P0191 (Fuel Rail Pressure Sensor A Circuit Range/Performance) is: Faulty fuel rail pressure sensor A providing inaccurate readings due to internal calibration drift or contamination on the sensing diaphragm
Typical repair costs for P0191 range from $150 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Incorrect fuel rail pressure can lead to lean or rich running conditions, causing engine misfires, reduced power, and potential catalytic converter damage from unburned fuel. Severe lean conditions could cause engine overheating.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0191 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel Delivery System
Difficulty
Type
Generic (SAE)
Recommended Tools
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