P0491 fault code: what it means

P0491: Secondary air injection system fault, bank 1 (older petrol engines). Cold start emission system.

Engine and gearbox (powertrain) · Minor

Usual causes, most likely first

secondary air pump failed
secondary air valve stuck
hose leak or blockage

P0491 by make

BMW

Secondary air injection system fault, bank 1 (older petrol engines). Cold start emission system.

Usual causes: secondary air pump failed; secondary air valve stuck; hose leak or blockage

What the repair usually costs

Glow plugs (diesel, set of 4)NZ$250–NZ$850 · A$250–A$850

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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.