2003 Hummer H2 Oxygen Sensor Bank 1

JSEEFRIED

MEMBER
2003 HUMMER H2
V8
4WD
AUTOMATIC
73,000 MILES

I received a P0135 code after getting a check engine light. I replaced both O2 sensors before the cat and both of them after the catalytic convertor. I still had a P0135 code come back. So I checked the fuses for both 02 heater circuits and they are good. What could be the problem with the error? Engine runs fine by the way and seems to have no other issues.

1 Reply

FACTORYJACK

MECHANIC
4,159 POSTS

Check that power is getting to the fuse(s), I am showing O2A is the fuse designation. Power to the fuse comes from the ignition 1 circuit. If there is power to the fuse, identify which wires are heater power and ground and check that a test lamp lights at the sensor connector(harness side). I show pink and black/white being the heater circuit for bank 1 sensor 1. The ECM supplies the ground for the sensor, and it monitors the current from that side. My guess is, you have a poor connection via a terminal, a wire is open, or you have a faulty ECM. If you can determine whats missing, power or ground, you would need to check individual wire resistances for the two circuits. If the wires show continuity, then you have a faulty ECM. The pink wire goes to the underhood fuse panel pin D8 of connector C2, and the BLK/WHT goes to ECM pin 72 of connector C2.

Oxygen Sensor Bank 1 and Bank 2 Are usually caused by lack of fuel, have you changed the fuel filter? It may also be a weak fuel Pump, or a bad temperatures sending unit.