VOLVO
ECM-2A0A - Rear heated oxygen sensor (HO2S). Signal missing. Intermittent fault
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:
9 modelsC70 Cabriolet (1998–2005), C70 Coupé (1998–2002), S60 (2001–2009), S70 (1997–2000), S80 (1999–2006), V70 (1997–2000), V70 (2000–2008), V70 XC (1998–2000), V70 XC / XC70 (2001–2007)
Show models by year and engine (22)
- Volvo C70 Cabriolet (1998–2005)1999, 2001–2005
- Volvo C70 Cabriolet (1998–2005)2000All engines except: B5244S
- Volvo C70 Coupé (1998–2002)1999All engines except: B5254S DENSO
- Volvo C70 Coupé (1998–2002)2000All engines except: B5244S
- Volvo C70 Coupé (1998–2002)2001–2002
- Volvo S60 (2001–2009)2001All engines except: B5244S, B5244S2, D5244T
- Volvo S60 (2001–2009)2002–2003Engine B5204T5, B5234T3, B5234T7, B5244T3 only
- Volvo S60 (2001–2009)2004Engine B5204T5, B5234T3, B5234T7 only
- Volvo S70 (1997–2000)1999Engine B5204T3, B5204T4, B5234T3, B5234T7, B5254T only
- Volvo S70 (1997–2000)2000Engine B5204T3, B5204T4, B5234T3, B5234T7, B5244T only
- Volvo S80 (1999–2006)1999–2000All engines except: B5244S, B5244S2, D5252T MSA 15.8
- Volvo S80 (1999–2006)2001Engine B5204T5, B5234T7, B5244T3, B6284T, B6294S only
- Volvo S80 (1999–2006)2002–2003Engine B5204T5, B5234T7, B5244T3, B6294S2, B6294T only
- Volvo S80 (1999–2006)2004Engine B5204T5, B5234T7, B6294S2, B6294T only
- Volvo V70 (1997–2000)1999Engine B5204T3, B5204T4, B5234T3, B5234T7, B5234T8, B5254T only
- Volvo V70 (1997–2000)2000All engines except: B5244S, B5244S2, B5244SG, B5244SG2, D5252T MSA 15.8
- Volvo V70 (2000–2008)2000All engines except: D5252T MSA 15.8
- Volvo V70 (2000–2008)2001–2003Engine B5204T5, B5234T3, B5234T7, B5244T3 only
- Volvo V70 (2000–2008)2004Engine B5204T5, B5234T3, B5234T7 only
- Volvo V70 XC (1998–2000)1999–2000
- Volvo V70 XC / XC70 (2001–2007)2001–2002
- Volvo V70 XC / XC70 (2001–2007)2003–2004Engine B5234T7 only
What does this fault code mean?
The signal from the rear oxygen sensor is missing, so the fault is set. The fault is intermittent, meaning it has occurred at some point but may not be present now. The cause may be an open circuit in the signal or ground wire, or contact resistance or oxidation in the connector.
Possible causes
- Open circuit in the signal wire
- Open circuit in the ground wire
- Poor contact or oxide in the connector
What you can do
- 1Do not use rust solvent or grease on the sensor connector. Check that it is secure and clean, without play
- 2With the car switched off, use a multimeter to check that the signal and ground wires are not broken
- 3If you have a diagnostic tool: read the rear sensor signal in live data with the engine idling. A signal that is missing or irregular points to the sensor or wiring
- 4If the connector and wires are in order but the fault remains, have a workshop try a new rear oxygen sensor
Symptoms you may notice1
- Malfunction indicator lamp (MIL) lit
What the fault can affect2
- Twin oxygen sensor control is switched off
- Catalytic converter diagnostics are switched off
General guidance for car owners. Diagnosis on the car can point to a different cause.