The heated oxygen (HO2S) bank 2 sensor 1 is threaded into the cylinder 2, 4, 6 exhaust manifold (cylinders 2, 4, 6 are closest to radiator). The sensor is equipped with a heater element to decrease the amount of time required to enter closed loop fuel control. The ECM controls the heater by pulsing circuit 551 to ground. When the heater is commanded Off (circuit not grounded), the voltage level at the ECM should be high (ignition voltage). When the heater is commanded On (circuit grounded), the voltage level at the ECM should be low. The ECM heater feedback circuit uses a pull-up voltage (1.6-3.6 volts), which allows the ECM to individually differentiate between an open, short to ground or short to voltage. DTC P0155 will set if the ECM detects HO2S bank 2 sensor 1 does not become active within a certain length of time of the exhaust temperature reaching 600°C (1112°F).

DTC P0155 will set if the ECM detects HO2S bank 1 sensor 1 does not become active within 20 seconds when:

DTC P0155 diagnostic runs continuously once the above conditions have been met.

P0155 is a (type B) DTC

To locate an intermittent problem, use scan tool to monitor HO2S BANK 2 SEN. 1 HEATER with engine running. The voltage should fluctuate greater than 1 volt indicating the circuit is functioning correctly. Compare this parameter to HO2S BANK 1 SEN. 1 HEATER parameter. Both parameters should closely match. The voltage will not change greater than 1 volt when an open circuit occurs.

Heater element resistance: 2.4-9.2 ohms