P2178 fault code: what it means

P2178: System too rich off idle, bank 1.

Engine and gearbox (powertrain) · Minor

Usual causes, most likely first

leaking injector
faulty MAF sensor
high fuel pressure
faulty front O2 sensor

P2178 by make

Volvo

Long-term fuel trim at its lower limit: the engine is running rich.

Usual causes: leaking injector; faulty MAF sensor; EVAP purge valve stuck open

What the repair usually costs

Air-fuel ratio / front O2 sensor replace (upstream)NZ$270–NZ$750 · A$260–A$730
O2 sensor replace (downstream / after cat)NZ$180–NZ$480 · A$180–A$460
MAF (mass air flow) sensor replaceNZ$170–NZ$660 · A$160–A$600
High-pressure fuel pump (GDI petrol or common-rail diesel)NZ$1,140–NZ$4,280 · A$1,060–A$3,800

Not sure what P2178 means on your car? Ask Credov.

Before you clear it

Write the code down or photograph the scanner first. A code that comes straight back after clearing points to a fault that is still there. A car whose codes were cleared just before you arrived may be hiding one: the scanner's readiness monitors show "not ready" for a while after codes are cleared.

Researched by Credov from manufacturer and workshop sources. A fault code points to where a fault may be; a workshop confirms it with a diagnosis. Browse all fault codes.