P0040 fault code: what it means

P0040: Front oxygen sensor plugs swapped between banks. Common after sensor replacement.

Engine and gearbox (powertrain) · Minor

Usual causes, most likely first

1. oxygen sensor plugs swapped
2. wrong harness routing

P0040 by make

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

Not sure what P0040 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.