VOLVO
ECM-0420 - Three-way catalytic converter (TWC) efficiency, bank 1.Signal too low
System
Engine Control Module (ECM)
Volvo models this fault code applies to
This fault code has different meanings depending on model, model year or engine. Select the meaning that applies to your car.
Applies to the following models:
3 modelsC30 (2007–2013), S40 (2004–2013), V50 (2004–2013)
Show models by year and engine (14)
- Volvo C30 (2007–2013)2007–2009Engine B4164S3, B4184S11, B4184S8, B4204S3 only
- Volvo C30 (2007–2013)2010Engine B4164S3, B4184S11, B4184S8, B4204S3, B4204S4 only
- Volvo C30 (2007–2013)2011–2012Engine B4164S3, B4204S3, B4204S4 only
- Volvo C30 (2007–2013)2013Engine B4204S3, B4204S4 only
- Volvo S40 (2004–2013)2005Engine B4164S3, B4184S11 only
- Volvo S40 (2004–2013)2006Engine B4164S3, B4184S11, B4184S8 only
- Volvo S40 (2004–2013)2007–2009Engine B4164S3, B4184S11, B4184S8, B4204S3 only
- Volvo S40 (2004–2013)2010Engine B4164S3, B4184S11, B4184S8, B4204S3, B4204S4 only
- Volvo S40 (2004–2013)2011–2012Engine B4164S3, B4204S3, B4204S4 only
- Volvo V50 (2004–2013)2005Engine B4164S3, B4184S11 only
- Volvo V50 (2004–2013)2006Engine B4164S3, B4184S11, B4184S8 only
- Volvo V50 (2004–2013)2007–2009Engine B4164S3, B4184S11, B4184S8, B4204S3 only
- Volvo V50 (2004–2013)2010Engine B4164S3, B4184S11, B4184S8, B4204S3, B4204S4 only
- Volvo V50 (2004–2013)2011–2012Engine B4164S3, B4204S3, B4204S4 only
What does this fault code mean?
The control module checks the efficiency of the catalytic converter on bank 1 by comparing the signal from the rear oxygen sensor with the front one. If the converter performs below a set level, the fault is recorded. The causes may be misfires, leaks in the intake or exhaust system, faulty fuel pressure or uneven compression, but also an aged or damaged converter.
Possible causes
- Misfiring
- Air leakage in the intake system
- Leakage in the exhaust system
- Faulty fuel pressure
- Uneven compression
- Aged or damaged catalytic converter
What you can do
- 1Read out the fault code, erase it and road-test to see whether it returns
- 2Look for air leaks in the intake system, such as cracks in hoses and at connections
- 3Look for leaks in the exhaust system, such as soot around joints and clamps
- 4If you have a diagnostic tool, read the misfire counters in live data, since misfires can damage the catalytic converter
- 5If the intake and exhaust systems are sealed, have a workshop check the fuel pressure and compression, and replace the converter if the fault remains
Symptoms you may notice1
- The malfunction indicator lamp (MIL) is lit
General guidance for car owners. Diagnosis on the car can point to a different cause.