VOLVO
ECM-2A2A - Rear heated oxygen sensor (HO2S) preheating. Faulty signal
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:
6 modelsC70 Cabriolet (1998–2005), S60 (2001–2009), S80 (1999–2006), V70 (2000–2008), V70 XC / XC70 (2001–2007), XC90 (2003–)
Show models by year and engine (11)
- Volvo C70 Cabriolet (1998–2005)2003–2005
- Volvo S60 (2001–2009)2002–2003Engine B5204T5, B5234T3, B5234T7, B5244T3 only
- Volvo S60 (2001–2009)2004Engine B5204T5, B5234T3, B5234T7, B5254T4 only
- Volvo S80 (1999–2006)2002Engine B5204T5, B5234T7, B5244T3, B6294S2, B6294T only
- Volvo S80 (1999–2006)2003Engine B5204T5, B5234T7, B5244T3, B5254T2, B6294S2, B6294T only
- Volvo S80 (1999–2006)2004Engine B5204T5, B5234T7, B6294S2, B6294T only
- Volvo V70 (2000–2008)2002–2003Engine B5204T5, B5234T3, B5234T7, B5244T3 only
- Volvo V70 (2000–2008)2004Engine B5204T5, B5234T3, B5234T7, B5254T4 only
- Volvo V70 XC / XC70 (2001–2007)2002
- Volvo V70 XC / XC70 (2001–2007)2003–2004Engine B5234T7 only
- Volvo XC90 (2003–)2003–2004All engines except: D5244T
What does this fault code mean?
The engine control module (ECM) has registered a faulty signal from the preheating of the rear oxygen sensor. The fault can be caused by contact resistance, oxidation or a defective sensor.
Possible causes
- Contact resistance and oxidation in the connections
- Defective rear oxygen sensor
What you can do
- 1Read the code, clear it and road test to see whether it returns
- 2Check that the connector at the rear oxygen sensor is secure and not oxidised or showing contact resistance
- 3Try a new rear oxygen sensor if the fault is not cleared by the connector check
- 4If the fault returns, have a workshop check the sensor signal with diagnostic equipment
Symptoms you may notice1
- The malfunction indicator light (MIL) comes on
General guidance for car owners. Diagnosis on the car can point to a different cause.