CodelampTwo codes together
P0420 and P0141 together: the converter test and its sensor
P0420
- In plain words
- The catalytic converter on bank 1 is not cleaning the exhaust as well as it should.
- Standard name
- Catalyst System Efficiency Below Threshold (Bank 1)
- System
- Catalytic converter and oxygen sensors
P0141
- In plain words
- The heater in the rear oxygen sensor, the one that watches the catalytic converter, has a fault.
- Standard name
- O2 Sensor Heater Circuit (Bank 1 Sensor 2)
- System
- Catalytic converter and oxygen sensors
General information, not a mechanic's diagnosis: have a mechanic confirm before any repair.
What the computer saw
P0141 says the heater in the rear oxygen sensor on bank 1 has a fault. That sensor is the one that judges the catalytic converter for P0420. A sensor that cannot heat up reads poorly, so the converter may not be the problem at all.
Likely causes, most common first
- A failed rear oxygen sensor. Its heater burned out, and its readings are unreliable. The most common cause of this pair.
- Wiring or a fuse for the sensor heater. A broken wire or blown fuse stops the heater.
- A worn catalytic converter as well. Possible, but judged only once the sensor works.
What you can note yourself
- Read every code, including pending ones.
- Note whether any exhaust work was done recently, which can damage sensor wiring.
What to tell the shop
- Both codes.
- Ask them to fix the sensor heater fault and retest before quoting a converter.
This page gives no verdict on whether a car is safe to drive; a mechanic can.