P048A

What it means

P048A means the powertrain control module has found that Exhaust Pressure Control Valve 'A' is stuck closed. The module commands the valve to a position and compares the exhaust pressure or valve position feedback with what it expects. If the valve does not open as commanded, or the pressure stays too high, the code is set. The valve's location and function depend on the engine, as it is mostly found on diesels.

Symptoms

• Engine warning light on
• Loss of power or the car going into limp mode
• Poor acceleration or hesitation under load
• Turbo not building or holding boost as normal
• Higher than normal exhaust smoke or rough running
• Increased fuel consumption

Possible causes

• Exhaust pressure control valve seized or sticking due to carbon and soot build-uplikely
• Faulty valve actuator or motor (electric, vacuum or other type depending on the engine)likely
• Damaged wiring, corroded connector or poor earth or supply to the valvepossible
• Faulty exhaust pressure sensor or valve position sensor giving a wrong readingpossible
• Vacuum supply fault such as a split hose, leaking solenoid or weak pump, on vacuum-operated valvespossible
• Blocked exhaust components downstream, such as a clogged particulate filter or catalyst, raising pressurepossible
• Control module fault or outdated softwarerare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting load, engine speed and temperature when the code set, and look for related turbo, boost, particulate filter or pressure sensor codes.
2. Check for manufacturer service information or bulletins for the specific model and engine, as valve design and location vary.
3. Visually inspect the valve, its linkage, wiring, connector and any vacuum hoses for damage, heat damage, corrosion, splits or soot leaks.
4. With a suitable scan tool, command the valve through its range and compare commanded with actual position, and listen and watch for movement.
5. Check the exhaust pressure sensor and valve position sensor readings against specification with the engine off and then running.
6. Test the valve's power supply, earth and control signal at the connector, and check for wiring continuity and shorts.
7. On vacuum-operated valves, test the vacuum supply and control solenoid against the manufacturer's specification.
8. Check for exhaust restrictions such as a clogged particulate filter, using differential pressure data and the manufacturer's procedure.

How to fix

• Free or clean the valve only where the manufacturer permits it; otherwise replace the seized valve.
• Replace the faulty actuator or valve assembly if it fails the commanded movement test.
• Repair or replace damaged wiring, terminals or connectors, and clear any corrosion.
• Replace a faulty exhaust pressure or position sensor.
• Repair vacuum leaks or replace the faulty vacuum solenoid or pump.
• Rectify any exhaust restriction found, using the manufacturer's approved procedure, and update the control module software only if a bulletin identifies it as a cause.

Can I keep driving?

Nearby codes

• P0489GenericEGR A Control Circuit Low
• P048BGenericExhaust Pressure Control Valve A Position Sensor/Switch Circuit