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DTC P0136: 1/2 O2 Sensor Heater Circuit Malfunction (4.0L With CALIF. Emissions): Testing

NOTE: 1/2 HO2S is located in front exhaust pipe below front mini-catalytic converter and may also be referred to as a downstream oxygen sensor.
  1. Turn ignition on. Using scan tool, check for DTCs. If DTC SPECIFIC GOOD TRIP counter is displayed and displayed count is "0", go to next step. If DTC SPECIFIC GOOD TRIP counter is not displayed or displayed count is not "0", go to step  9 .
  2. Turn ignition off. Remove and inspect fuse No. 17 (20-amp) fuse from Power Distribution Center (PDC) located in right side of engine compartment, next to battery. See Figure . If fuse is okay, go to step  4 . If fuse is blown, go to next step.
  3. Remove HO2S downstream heater relay from PDC. See Figure . Measure resistance between ground and terminal C16 (Red wire) at HO2S downstream heater relay socket in PDC. See Figure . If resistance is 5 ohms or more, circuit is okay. Replace fuse. If resistance is less than 5 ohms, repair short to ground in Red wire. Replace fuse.
  4. Remove HO2S downstream heater relay from PDC. See Figure . Measure resistance between terminals No. 85 and 86 at downstream heater relay. See Figure . If resistance is 100 ohms or less, go to next step. If resistance is more than 100 ohms, replace relay.
  5. Measure resistance of Red wire between terminal C16 at HO2S downstream heater relay socket in PDC and terminal A22 at fuse holder for fuse No. 17 in PDC. See Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Red wire.
  6. Ensure ignition is off. Disconnect Powertrain Control Module (PCM) connectors. PCM is located in engine compartment on left front fender, near radiator support. Measure resistance of Brown/Violet wire between terminal C20 at HO2S downstream heater relay socket in PDC and terminal No. 9 at PCM C3 connector. See Figure and Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Brown/Violet wire.
  7. Measure resistance between ground and terminal C20 (Brown/Violet wire) at HO2S downstream heater relay socket in PDC. See Figure . If resistance is 5 ohms or more, go to next step. If resistance is less than 5 ohms, repair short to ground in Brown/Violet wire. See WIRING DIAGRAMS article.
  8. At this time, PCM is assumed to be defective. Replace PCM.
  9. It is assumed that there is an intermittent problem with wiring harness and/or connectors. Visually inspect all related connectors and wiring harness for any possible problems. Also, check for any related technical service bulletins.
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