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DTC P0135: Heated Oxygen Sensor (Ho2S) No. 1 Heater Circuit Malfunction

  1. Disconnect HO2S No. 1 harness connector. Using DVOM, measure resistance between terminals No. 3 and 4 of HO2S No. 1. See Fig 1 . On vehicles with warm-up three-way catalytic converters (WU-TWC), resistance should be between 4.5-5.7 ohms. On vehicles without WU-TWCs, resistance should be 11.7-14.3 ohms. If resistance is as specified, go to next step. If resistance is not as specified, replace HO2S No. 1 and retest system.
    Fig 1: Testing HO2S No. 1 & HO2S No. 2
    G96E09875Courtesy of SUZUKI OF AMERICA CORP.
  2. Reconnect HO2S No. 1 harness connector. Turn ignition on. Measure voltage (backprobe) between ground and PCM harness connector terminal C51-2-4. See PIN VOLTAGE/CIRCUIT RESISTANCE CHARTS article for terminal identification. If voltage is 10-14 volts, go to next step. If voltage is not as specified, check Black/White wire or Gray wire for an open, Gray wire for a short to ground, or poor HO2S No. 1 harness connection. Repair as necessary. If wires are okay, replace PCM and retest system.
  3. Start engine and allow it to reach normal operating temperature. Measure voltage (backprobe) between ground and PCM harness connector terminal C51-2-4. If voltage is 0-1 volt, check for an intermittent problem. See TROUBLE SHOOTING - NO CODES article. If voltage is not as specified, check for poor PCM harness connection. If connection is okay, replace PCM and retest system.
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