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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 are not displayed at the same time, go to next step. If DTC P0135 and P0141 are displayed at the same time, turn ignition off. Disconnect ECM harness connector. Check resistance between ECM harness 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 greater than 5 ohms, repair open in harness between ECM and coupling connector, open in harness 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 greater, 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 harness and connector of ECM, repair contact in ECM connector. If wiggling harness and connector does not change reading, disconnect connector from front O2S. Check voltage between ECM harness connector terminal No. 38 and chassis ground. If voltage is one volt or less, replace ECM. If voltage is greater than one volt, check for short circuit in harness between ECM and front O2S connector. If circuit is okay, replace ECM.
  4. Turn ignition off. Disconnect front O2S harness connector. Turn ignition on. Check voltage between front O2S harness connector terminal No. 2 and chassis ground. If voltage is 10 volts or greater, 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 harness connector terminals No. 1 and 2. If resistance is greater than 30 ohms, replace O2S. If resistance is 30 ohms or less, repair open in harness 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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