Front heated oxygen sensor (HO2S)

Supplied directly after start with 5 V for approximately 30 seconds. After this the engine control module (ECM) lowers voltage to approximately 1V and depending on the oxygen level in the exhaust gases the engine control module (ECM) retains a voltage which is constantly in the region around 0.5V when Lambda = 1.

The output signal characteristic is between 0 - 1V.

Short-term fuel trim control area is very narrow and lies 0.990 and 1.010.

Signal characteristics

low voltage = rich mixture
high voltage = lean mixture

CAUTION: Because the output voltage from the front heated oxygen sensor (HO2S) to the engine control module (ECM) at Lambda = 1 is constantly around 0.5 V it can easily seem as if the fuel trim does not function and that fault-tracing is required. This is correct signal which has a narrow range so that the engine control module (ECM) can control the fuel/air mixture faster and more precisely using the linear output signal from the heated oxygen sensor (HO2S).