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DTC P0135 (FO2H): Front O2S Heater Circuit Malfunction

  1. Connect SSM and check for DTC(s). If DTC P0135 and P0141 do not exist, go to next step. If DTC P0135 and P0141 exist, turn ignition off. Disconnect ECM connector. Check resistance between ECM connector terminal No. 42 and chassis ground. See appropriate wiring diagram in WIRING DIAGRAMS article. If resistance is 5 ohms or less, repair poor contact in ECM connector. If resistance is more than 5 ohms, repair open in wiring between ECM and coupling connector, open in wiring between coupling connector and engine ground terminal, poor contact in front O2S or poor contact in coupling connector.
  2. Start engine. Set SSM function to mode F32 to read front O2S heater current indication. If reading is 0.2 amp or more, repair O2S connector and/or ECM connector. If current is less than 0.2 amp, go to next step.
  3. Start and idle engine. Using DVOM connected to chassis, backprobe ECM terminal No. 38. If voltage is one volt or less, go to next step. If voltage is one volt or less while wiggling wiring and connector of ECM, repair contact in ECM connector. If wiggling wiring and connector does not change reading, disconnect connector from front O2S. Check voltage between ECM connector terminal No. 38 and chassis ground. If voltage is one volt or less, replace ECM. If voltage is always more than one volt, check for short circuit in wiring between ECM and front O2S connector. Repair circuit and replace ECM.
  4. Turn ignition off. Disconnect front O2S connector. Turn ignition on. Check voltage between front O2S connector terminal No. 2 and chassis ground. If voltage is 10 volts or more, go to next step. If voltage is less than 10 volts, repair power supply line between main relay and front O2S. Check for poor terminal contact in main relay and O2S connector.
  5. Turn ignition off. Check resistance between front O2S connector terminals No. 1 and 2. If resistance is more than 30 ohms, replace O2S. If resistance is 30 ohms or less, repair open in wiring between front O2S connector and ECM connector. Check for poor contact in front O2S connector or poor contact in ECM connector.
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