What Does P0091 Mean?
The ECM has detected a low voltage or short-to-ground condition in the fuel pressure regulator 1 control circuit. The solenoid signal wire is reading below the expected threshold, which prevents the ECM from properly controlling fuel rail pressure. The driver may experience hard starting, poor idle quality, misfires, or reduced power, especially under load.
Safety Warning
Avoid driving if possible. The fuel pressure regulator cannot be properly controlled, which may cause the engine to run with incorrect fuel pressure. This can result in stalling, severe misfires, or catalytic converter damage. Have the vehicle diagnosed promptly.
Common Causes
35%
Short to ground in the wiring between the ECM and fuel pressure regulator solenoid
30%
Internally shorted fuel pressure regulator solenoid coil
20%
Water intrusion or corrosion at the regulator solenoid connector
15%
ECM driver circuit failure pulling the signal low
Diagnostic Steps
1
Disconnect the fuel pressure regulator solenoid and measure coil resistance. A reading significantly below spec indicates an internally shorted coil.
2
With the solenoid unplugged, check continuity between each wire in the harness and chassis ground. Continuity on the control wire indicates a short to ground.
3
Inspect the solenoid connector for moisture, corrosion, or green verdigris on the pins. Clean with electrical contact cleaner or replace the connector.
4
Trace the wiring harness and inspect for chafing against brackets, engine mounts, or other metal components that could create a ground path.
5
If the wiring and solenoid test normal, verify the ECM output by back-probing the ECM connector. If the ECM is pulling the line low internally, ECM replacement may be necessary.
Estimated Repair Cost
$200 - $1,100
Parts + labor, varies by vehicle and location
The ECM has detected a low voltage or short-to-ground condition in the fuel pressure regulator 1 control circuit. The solenoid signal wire is reading below the expected threshold, which prevents the ECM from properly controlling fuel rail pressure. The driver may experience hard starting, poor idle ...
The most common cause of P0091 (Fuel Pressure Regulator 1 Control Circuit Low) is: Short to ground in the wiring between the ECM and fuel pressure regulator solenoid
Typical repair costs for P0091 range from $200 to $1,100, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Avoid driving if possible. The fuel pressure regulator cannot be properly controlled, which may cause the engine to run with incorrect fuel pressure. This can result in stalling, severe misfires, or catalytic converter damage. Have the vehicle diagnosed promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0091 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel System
Difficulty
Type
Generic (SAE)
Recommended Tools
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