P039A fault code: what it means

P039A: SKYACTIV-D low compression detected in cylinder 1 during deceleration. Stored history; if rough running continues, test compression and injectors.

Engine and gearbox (powertrain) · Costly if missed

Usual causes, most likely first

carbon on valves / valve not sealing
injector leaking or sticking
worn rings or valve damage

P039A by make

Mazda

SKYACTIV-D low compression detected in cylinder 1 during deceleration. Stored history; if rough running continues, test compression and injectors.

Usual causes: carbon on valves / valve not sealing; injector leaking or sticking; worn rings or valve damage

What the repair usually costs

Compression and leak-down test with diagnosisNZ$140–NZ$420 · A$150–A$450
Engine replacement, reconditioned engine (4-cylinder)NZ$5,570–NZ$10,560 · A$5,070–A$9,720

Not sure what P039A 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.