1998 Mitsubishi Galant O2 sensor problems

Hi bdiedrich97,

Let me know the exact trouble code and I will get the diagnostic procedures for you.

DTC P0135: FRONT HEATED OXYGEN SENSOR (HO2S) HEATER CIRCUIT MALFUNCTION

1. Disconnect front Heated Oxygen Sensor (HO2S) connector. Connect Test Harness (MD998464 ) to front HO2S. Check continuity between ground and test harness terminals No. 1 (Red clip) and No. 3 (Blue clip) on Eclipse and Galant (California), or terminals No. 2 (Red clip) and No. 4 (Blue clip) on Galant (Federal). If continuity exists, go to next step. If continuity does not exist, replace front HO2S.

2. Start and warm engine until engine coolant temperature is 176 °F (80 °C) or more. Connect jumper wires between battery voltage and test harness terminal No. 1 (Red clip) and between ground and terminal No. 3 (Blue clip). Connect DVOM between test harness terminals No. 2 (Black clip) and No. 4 (White clip) on Eclipse and Galant (California), or terminals No. 1 (Black clip) and No. 3 (White clip) on Galant (Federal). Check front HO2S output voltage while repeatedly racing engine. If voltage is 0.6-1.0 volt, go to next step. If voltage is not as
specified, replace front HO2S.

3. Disconnect test harness. Turn ignition on. Check voltage between rear HO2S connector terminal No. 1 on Eclipse 2.0L and Galant (California), or No. 2 on Eclipse 2.4L and Galant (Federal). If battery voltage exists, go to next step. If battery voltage does not exist, check PCM connector and wiring harness between front HO2S connector and PCM.

4. Disconnect PCM connector. Turn ignition on. Check voltage between ground and PCM connector terminal No. 60 on Eclipse, or No. 90 on Galant. If battery voltage does not exist, check connectors and wiring harness between front HO2S connector and PCM. If battery voltage exists, check PCM connector. If PCM connector is okay, replace PCM.