VOLVO
ECM-2120 - Front heated oxygen sensor (HO2S), control element. 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:
7 modelsC70 Cabriolet (1998–2005), C70 Coupé (1998–2002), S60 (2001–2009), S70 (1997–2000), S80 (1999–2006), V70 (1997–2000), V70 (2000–2008)
Show models by year and engine (19)
- Volvo C70 Cabriolet (1998–2005)2000Engine B5244S only
- Volvo C70 Coupé (1998–2002)1999Engine B5254S DENSO only
- Volvo C70 Coupé (1998–2002)2000Engine B5244S only
- Volvo S60 (2001–2009)2001, 2009Engine B5244S, B5244S2 only
- Volvo S60 (2001–2009)2002Engine B5244S, B5244S2, B5244SG, B5244SG2 only
- Volvo S60 (2001–2009)2003–2005Engine B5244S, B5244S2, B5244S6, B5244SG, B5244SG2 only
- Volvo S60 (2001–2009)2006Engine B5244S, B5244S2, B5244S6, B5244SG only
- Volvo S60 (2001–2009)2007–2008Engine B5244S, B5244S2, B5244SG only
- Volvo S70 (1997–2000)1999Engine B5254S DENSO only
- Volvo S70 (1997–2000)2000Engine B5244S, B5244S2, B5244SG, B5244SG2 only
- Volvo S80 (1999–2006)1999–2000Engine B5244S, B5244S2 only
- Volvo S80 (1999–2006)2001, 2006Engine B5244S, B5244S2, B5244SG only
- Volvo S80 (1999–2006)2002–2005Engine B5244S, B5244S2, B5244SG, B5244SG2 only
- Volvo V70 (1997–2000)1999Engine B5254S DENSO only
- Volvo V70 (1997–2000)2000Engine B5244S, B5244S2, B5244SG, B5244SG2 only
- Volvo V70 (2000–2008)2001, 2007–2008Engine B5244S, B5244S2, B5244SG only
- Volvo V70 (2000–2008)2002Engine B5244S, B5244S2, B5244SG, B5244SG2 only
- Volvo V70 (2000–2008)2003–2005Engine B5244S, B5244S2, B5244S6, B5244SG, B5244SG2 only
- Volvo V70 (2000–2008)2006Engine B5244S, B5244S2, B5244S6, B5244SG only
What does this fault code mean?
The engine control module has detected that the control circuit for the front heated oxygen sensor is short-circuited to ground or voltage, or that the circuit is open. The sensor measures the oxygen content in the exhaust and is used to control the fuel mixture, so when the sensor circuit fails the fuel trim is switched off.
Possible causes
- Signal cable short-circuited to voltage
- Signal cable short-circuited to ground
- Open-circuit in the signal cable
- Damaged heated oxygen sensor or damaged control circuit for the sensor
- Poor contact or oxidation in the heated oxygen sensor connector
What you can do
- 1Read the status of the diagnostic trouble code and note what it shows; then clear the code and road test the car
- 2Check the connector on the heated oxygen sensor for contact resistance and oxidation; disconnect and reconnect it with clean, tight contacts
- 3Do not use rust solvent spray or grease in the heated oxygen sensor connector
- 4Inspect the wiring to the heated oxygen sensor for chafing, pinching and breaks, especially where it runs close to the exhaust pipe
- 5Have a diagnostic tool? Follow the front oxygen sensor value in live data with the engine running at idle and check whether it swings evenly after a while
- 6If the fault returns despite these checks, have a workshop check the wiring and replace the oxygen sensor if needed
Symptoms you may notice1
- The malfunction indicator lamp (MIL) comes on
What the fault can affect1
- The fuel trim is switched off, so the fuel mixture is controlled without feedback from the sensor
General guidance for car owners. Diagnosis on the car can point to a different cause.