P0091 — Pressure regulator A – control circuit low

The fuel pressure regulator A command monitor detects a low electrical condition. Actual pressure may be affected, but P0091 is not simply a low-pressure measurement.

Affected system: Powertrain

Symptoms

• Hard starting or no start if fuel delivery is affected.
• Engine warning lamp; reduced power or stalling.

Possible causes

• Short to ground, missing supply or high-resistance connection, depending on control design.
• Internal actuator or control-driver electrical fault after wiring is excluded.

What to check

• Identify fuel pressure regulator A by VIN and check wiring and subcodes before measuring.
• Save failure conditions and related codes; establish whether pressure regulator a is commanded when the fault returns.
• Inspect connector, heat/vibration-exposed wiring and shared supplies before replacing components.
• Test for ground shorts and supply voltage drops in the specified command state.
• Compare command and electrical response with engine specifications; verify the repair under the original conditions.

Also written as: P0091-00, P009100, PO091 (some scan tools add the fault-type byte, e.g. -00).