P1421 fault code: what it means

P1421: Secondary air system bank 1 fault.

Engine and gearbox (powertrain) · Minor

Usual causes, most likely first

1. failed secondary air pump
2. stuck valve
3. pump relay fault

P1421 by make

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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.