Catalyst efficiency on Nissan petrol — the front cat-back O2 sensor is the weakness on Micra K12, Note E11 and Qashqai J10.
Nissan P0420 — Catalyst efficiency on Nissan petrol — the front cat-back O2 sensor is the weakness on Micra K12, Note E11 and Qashqai J10. Typical UK independent garage cost: £180–£700.
What actually causes P0420 on a Nissan
Nissan front cat assemblies on these models are well known to crack internally — the substrate loosens and rattles when tapped. P0420 with a rattle when you tap the cat = replacement needed. Without rattle, try a rear lambda first.
Nissan engines that log P0420
- Micra K12 1.2 / 1.4
- Note E11 1.4 / 1.6
- Qashqai J10 1.6 petrol
- Juke F15 1.6 DiG-T
How we diagnose P0420 on a Nissan
- Tap test the cat with a rubber mallet — internal rattle = substrate failure
- Graph both lambdas on scan tool
- Trial rear lambda replacement if no rattle
- Buy type-approved direct-fit cat — universal cats fail MOT on most modern Nissans
The common misdiagnosis to avoid
Aftermarket universal cats (£90–£140) generally don't pass MOT emissions on UK Nissan petrols — buy a type-approved direct-fit unit (£280–£480) to avoid a second MOT failure.
Nissan P0420 repair cost in the UK
Expect £180–£700 including parts and labour at an independent garage. Main-dealer quotes on Nissan are usually higher for the same job, and the spread exists because the cheap cause and the expensive cause throw the same code — pay for the diagnosis before you pay for parts.
Bob's workshop tip
For MOT compliance always insist on a type-approved (e-marked) cat — keep the box and paperwork in the car for emission-test pushback.
Codes usually seen alongside P0420 on Nissan
- P0430
- P0171
Symptoms drivers report with P0420
- Engine warning light on steady, no obvious drivability change day-to-day
- 3–7 mpg drop over the last 2,000 miles with no other explanation
- Faint smell of sulphur / rotten eggs from the exhaust under load
- Muffled rattle inside the cat when you tap it with a rubber mallet (loose substrate)
- MOT emissions test fails on Lambda, CO or HC — the P0420 was already MIL-on at the pre-test
- Sudden loud exhaust roar from cold start = catalytic converter has been stolen, not worn
- Paired codes: P0430 (bank 2), P0171/P0174 (lean), P0300-series misfires, P0136/P0156 (lambda circuit)
Repairs that clear P0420
- Smoke-test exhaust for leaks
- Graph both lambda outputs at steady state
- Replace rear lambda as cheaper trial
- Replace cat with type-approved unit if confirmed
For the generic, all-makes explanation of this code — meaning, every known cause and UK cost bands — see our P0420 guide.