P0091 indicates the engine control module (PCM/ECM) has detected a voltage signal from the fuel pressure regulator control circuit that is lower than expected. This typically points to an electrical issue in the wiring, connector, or the fuel pressure regulator solenoid itself.
The solenoid may be internally shorted or open, causing a low voltage signal to the PCM. This is the most common cause of P0091.
Damaged, corroded, or shorted wiring between the fuel pressure regulator and the PCM can cause a low voltage reading. Check for chafing, breaks, or poor connections.
A weak or corroded ground connection for the fuel pressure regulator circuit can result in a low voltage signal.
If the circuit is fused or relay-controlled, a blown fuse or failed relay can interrupt power and cause a low voltage condition.
While uncommon, a faulty PCM/ECM could incorrectly interpret the signal or have an internal short. This should only be considered after all other causes are ruled out.
Driving with P0091 may lead to poor engine performance, reduced fuel economy, or stalling. It is best to diagnose and repair the issue promptly to avoid potential drivability problems or further damage.
No, the PCM/ECM is rarely the cause of P0091. The issue is almost always related to the fuel pressure regulator solenoid, wiring, or connectors. Replace the PCM/ECM only after all other possibilities are exhausted.
Disconnect the solenoid connector and use a multimeter to measure resistance across the solenoid terminals. Compare the reading to the manufacturer’s specifications. If the resistance is out of range, the solenoid is likely faulty.
The code may clear temporarily if the issue is intermittent, but it will likely return if the underlying problem is not fixed. Proper diagnosis and repair are necessary to resolve the code permanently.