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 front of radiator). The sensor monitors the oxygen content in the exhaust gas before the pre-converter. The ECM supplies a variable output pump current to circuit 1664 in order to maintain a constant voltage level at the input pump current circuit 1666. As output pump current passes through the oxygen sensor when the sensor is operating above 300°C (572°F), the sensor will vary resistance according to changes in exhaust oxygen content. If oxygen content increases (lean air/fuel ratio) the resistance of the sensor increases which requires more current to maintain a constant voltage level. The ECM calculates a lambda value (actual air/fuel ratio divided by 14.6 to 1) based on the input pump current voltage level on circuit 1666 and the signal voltage level on circuit 1653. DTC P0154 will set when consecutive HO2S bank 2 sensor 1 lambda values differ more than a calibrated value over several readings.

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.