Pick a colour. The page changes, like the app does.
Officially? A wall of jargon. To most people? Absolutely nothing. That's exactly why we built the app.
Plug into any code reader and you'll get the same line every other app shows you. Technically correct. Practically useless.
"The same heater fault as P0135, but in the rear oxygen sensor, the one after the catalytic converter. Its heater's stopped working, so the sensor is slow to wake up on cold starts. Here's the honest good news: the rear sensor doesn't control your fuelling, it only monitors the cat's health. So the car runs exactly as it should. The only real-world consequence is the engine light and the MOT problem that comes with it. Check the fuse and wiring first (on many cars the heaters share a fuse), then it's a sensor swap."
Worth checking in roughly this order. Don't jump straight to the expensive fix:
The code itself is a snapshot. The fault sets after the car's watched the numbers over a whole drive cycle. Here's what's worth keeping an eye on:
Illustrative panels. These readings aren’t in our free demo drive, but the app shows them live from your own car.
Codes rarely tell the whole story. The clever part is reading them together, and against your exact car. Here's the kind of thing it catches:
The same heater fault as P0135, but in the rear oxygen sensor, the one after the catalytic converter. Its heater's stopped working, so the sensor is slow to wake up on cold starts. Here's the honest good news: the rear sensor doesn't control your fuelling, it only monitors the cat's health. So the car runs exactly as it should. The only real-world consequence is the engine light and the MOT problem that comes with it. Check the fuse and wiring first (on many cars the heaters share a fuse), then it's a sensor swap.
Yes, it's safe to drive. This is the most benign code in the O2 family. The rear sensor only watches the cat; it doesn't steer the fuelling, so the engine runs completely normally. The engine light is the whole problem, and that's an MOT fail item while it's lit. Get it sorted at your next service.
A rear O2 sensor is typically £30-100, often a touch cheaper than the front one, plus modest fitting. If the fuse or a corroded connector is the culprit, next to nothing. The sensor being seized into the exhaust is the usual complication, and garages handle that daily.
A lit engine management light is an MOT fail item, even when the fault behind it changes nothing about how the car drives. That's really the reason to fix this one, so fix the fault first and time it before your test is due.
Free app. Plug in, and get every code in plain English, plus the connections you'd never spot.