VOLVO
ECM-28AA - Front heated oxygen sensor (HO2S), bank 1. Signal too low
System
Engine Control Module (ECM)
Volvo models this fault code applies to
Applies to the following models:
2 modelsS40 (2004–2013), V50 (2004–2013)
Show models by year and engine (2)
What does this fault code mean?
Although the code is named signal too low, it is set when the readings of the front and rear oxygen sensors do not agree, or when the front sensor signal indicates a mixture that is incorrect compared with what the control module expects. The problem could sit in either the front or rear sensor circuit, or in the exhaust system.
Possible causes
- Leakage in the exhaust system
- Damaged oxygen sensor
- Poor contact or oxidation in the connections
- Short circuit to supply voltage or ground in the signal wire (-)
What you can do
- 1Check the exhaust system for air leaks, for example at joints, gaskets and around the oxygen sensors
- 2Check that the sensor connectors are clean and secure. Do not use rust solvent or grease on them
- 3If the exhaust is sealed but the fault remains, have a workshop replace the oxygen sensors as needed, since the code can also be set by a defective front or rear sensor
Symptoms you may notice1
- Malfunction indicator lamp (MIL) lit
What the fault can affect2
- 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.