Fault code P0173 – a step-by-step guide to diagnosing and fixing it

Error code P0173 is displayed and the check engine light is on - what does this mean?

The OBD/EOBD system detects a problem with the fuel trim in bank 2 with DTC P0173, which indicates that the air/fuel mixture is too lean. This fault code affects the fuel system, the oxygen sensors and the engine control unit on V6 and V8 engines. This code can have different priorities for different manufacturers, with German premium manufacturers in particular reacting sensitively to mixture faults.

What causes can this error code have?

• Defective oxygen sensor (lambda sensor) in bank 2
• Blocked or defective fuel injectors
• Leaks in the intake tract
• Defective fuel pump or low fuel pressure
• Dirty mass air flow sensor (MAF sensor)
• Damaged vacuum system
• Defective fuel pressure regulator
• Clogged fuel filter
• Loose or corroded plug connections
• Defective engine control unit (ECU)

What symptoms occur in parallel with fault code P0173?

• Uneven idling: The engine runs unevenly at idle speed
• Loss of power: Noticeable reduction in engine power, especially under load
• Increased fuel consumption: The vehicle requires more fuel than usual
• Starting problems: Difficulty starting the engine, especially when the engine is cold
• Jerking when accelerating: Uneven power delivery during acceleration
• Black smoke from the exhaust: Visible exhaust emissions due to incomplete combustion

How can the problem with error code P0173 be rectified?

• Repairing the P0173 error code requires a systematic diagnosis of the affected components.
• Check and replace oxygen sensors: Test all lambda sensors in bank 2 with a multimeter and replace defective sensors with original parts
• Clean the fuel system: Have fuel injection nozzles professionally cleaned or replace them completely if they are very dirty
• Check the intake tract for leaks: Check all hoses, seals and connections between the air filter and intake manifold and replace damaged parts
• Clean or replace the mass air flow sensor: Clean MAF sensor with special cleaner or replace with new sensor if defective
• Measure fuel pressure and check pump: Perform fuel pressure test and replace fuel pump or pressure regulator if pressure is insufficient
• Replace fuel filter: Replace the old filter with a new one and also check the fuel lines for blockages