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DTC P0135: O2 Sensor 1/1 Heater Failure

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION . For wiring diagram, see WIRING DIAGRAMS article.
NOTE: The 1/1 O2 sensor is referred to as upstream oxygen sensor in this test. Upstream oxygen sensor heater monitor runs during oxygen sensor cool-down period, after a hot drive cycle or when engine is shut down with ignition off. DTC may be stored in Powertrain Control Module (PCM) if upstream oxygen sensor signal voltage is different when heater is commanded on as compared to when heater is off. Possible causes are: defective upstream oxygen sensor or heater, defective Auto Shutdown (ASD) relay output circuit, or defective connectors or wiring.
  1. Using scan tool, check for DTCs. If global good trip counter is displayed and equal to zero, go to next step. If global good trip counter is not displayed and equal to zero, go to step  6.
  2. Turn ignition off. Disconnect upstream oxygen sensor connector. Upstream oxygen sensor is located on the exhaust manifold. Turn ignition on with engine off. With scan tool in SENSORS mode, actuate O2 HEATER TEST. Using voltmeter, check voltage at ASD relay Dark Green/Orange wire. ASD relay is located in Power Distribution Center (PDC). If voltage is more than 11 volts, go to next step. If voltage is 11 volts or less, repair open Dark Green/Orange wire between ASD relay and upstream oxygen sensor. Perform TEST VER-5A .
  3. Turn ignition off. Disconnect PCM connectors. PCM is located at driver's side front corner of engine compartment, between battery and fender. Using ohmmeter, check resistance of Dark Blue/Yellow wire between ASD relay and PCM terminal No. 67. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open Dark Green/Yellow wire. Perform TEST VER-5A .
  4. Check resistance between ground and PCM connector terminal No. 67 (Dark Blue/Yellow wire) If resistance is less than 5 ohms, repair short to ground on Dark Blue/Yellow wire between ASD relay and PCM. Perform TEST VER-5A . If resistance is 5 ohms or more, go to next step.
  5. Check resistance between upstream oxygen sensor connector (harness side) terminals No. 1 (Dark Green/Orange wire) and No. 2 (Orange/Red wire). If resistance is 4-7 ohms, replace PCM. Perform TEST VER-5A . If resistance is not 4-7 ohms, replace upstream oxygen sensor. Perform TEST VER-5A .
  6. Inspect wiring and connectors between upstream oxygen sensor and PCM. Inspect related wiring harnesses and connectors. Refer to Technical Service Bulletins (TSBs) for related problems. If no problems exist, test is complete. If any problems exist, repair wiring or connectors as necessary. Perform TEST VER-5A .
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