VOLVO
ECM-4901 - Three-way catalytic converter (TWC) efficiency, bank 2. Intermittent fault
System
Engine Control Module (ECM)
Volvo models this fault code applies to
Applies to the following models:
1 modelS80 (1999–2006)
What does this fault code mean?
The catalytic converter on bank 2 deviated too much at an earlier point, but the engine control module can no longer detect the fault. The fault is intermittent, meaning it comes and goes, and it may already be gone when you read the code.
Possible causes
- Misfiring in the engine
- Air leak in the intake on bank 2
- Leak in the exhaust system
- Fuel pressure is wrong
- Uneven compression in the engine
- Catalytic converter is defective
What you can do
- 1Read off the fault code and note it, erase it and test-drive to see whether it returns
- 2If it does not return, the fault is probably temporary, and no further troubleshooting is needed beyond keeping an eye on it
- 3Check the intake and exhaust systems for leaks such as cracks or loose joints
- 4Have a workshop check fuel pressure and compression if the fault comes back
Symptoms you may notice1
- Emissions warning lamp (MIL) lit
What the fault can affect1
- Control of the rear oxygen sensor is switched off
General guidance for car owners. Diagnosis on the car can point to a different cause.