Damaged, corroded or loose wiring or connector at the fuel pressure regulator; Faulty fuel pressure regulator or pressure control valve (open-circuit coil or stuck); Poor power or earth supply to the regulator circuit, including a blown fuse or faulty relay where fitted; Fuel pressure sensor giving an incorrect reading so the control unit cannot regulate properly; Low fuel pump output or restricted fuel filter affecting pressure control; Internal driver fault in the engine control unit; Outdated or faulty control unit software on a model with a known issue.

P0090

Fuel Pressure Regulator A Control Circuit/Open.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
0: AreaFuel and air metering, auxiliary emission controls
90: FaultThe specific fault in that area

What it means

P0090 means the engine control unit has detected an open circuit or a fault in the control circuit of fuel pressure regulator A. The control unit commands the regulator and monitors the circuit, and it sets the code when the expected electrical response is missing or the actual fuel pressure cannot be controlled to the target. The exact regulator type and location depend on the engine and fuel system.

Symptoms

Engine warning light on
Hard starting or long cranking
Rough idle or misfire
Hesitation or lack of power under load
Engine stalling or cutting out
Poor fuel economy

Possible causes

Damaged, corroded or loose wiring or connector at the fuel pressure regulatorlikely
Faulty fuel pressure regulator or pressure control valve (open-circuit coil or stuck)likely
Poor power or earth supply to the regulator circuit, including a blown fuse or faulty relay where fittedpossible
Fuel pressure sensor giving an incorrect reading so the control unit cannot regulate properlypossible
Low fuel pump output or restricted fuel filter affecting pressure controlpossible
Internal driver fault in the engine control unitrare
Outdated or faulty control unit software on a model with a known issuerare

How to diagnose

Read all stored codes and freeze frame data, noting engine speed, load and temperature when the code set, and check for related fuel pressure or rail codes
Visually inspect the regulator wiring and connector for chafing, corrosion, water ingress, bent pins and poor retention
Check the relevant fuses and relays and confirm the regulator has a correct supply and earth with the ignition on
Measure the regulator coil resistance and compare it with the manufacturer's specification for that engine
Check the wiring between the regulator and control unit for open circuits, short circuits and high resistance
Compare live fuel pressure data with the target value, and verify with a mechanical gauge if the system allows
Check the fuel pressure sensor reading against actual pressure and inspect the fuel filter and pump output
Check for applicable software updates or technical bulletins for the model and engine

How to fix

Repair or replace damaged wiring and clean or replace the connector terminals
Replace the fuel pressure regulator or pressure control valve if it fails electrical or functional tests
Replace the faulty fuse or relay after finding why it failed
Replace the fuel pressure sensor if its readings are wrong
Replace a clogged fuel filter or weak fuel pump as the testing shows
Update the control unit software only if a known fault with the existing calibration is documented for that vehicle

Can I keep driving?

Medium severity

The car may run with reduced performance, but poor fuel pressure control can cause stalling and hard starting, so get it fixed soon. Avoid long journeys or driving in traffic if it is cutting out or losing power.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.