LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Jeep >> 2002 >> Wrangler X, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0136: 1/2 O2 Sensor Heater Circuit Malfunction >> Testing
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC P0136: 1/2 O2 Sensor Heater Circuit Malfunction: Testing

  1. Turn ignition on, engine not running. With the DRBIII®, read DTCs. Is the DTC Good Trip counter displayed and equal to zero? If yes, go to next step. If no, go to step  7.
  2. Turn ignition off. Remove the O2 Sensor Downstream Heater Relay from Power Distribution Center (PDC). Turn ignition on, engine not running. Using a 12-volt test light connected to ground, probe the ASD output voltage terminal of the O2 Heater Relay pin in the PDC. Does the test light illuminate brightly? If yes, go to next step. If no, repair the Heater Relay Supply circuit for an open and/or short to ground. Also check fuse No. 16 (15-amp) in the PDC.
  3. Turn the ignition off. Disconnect the PCM harness connectors. Measure the resistance of the O2S Heater Relay Control circuit from the O2 Sensor Downstream Heater Relay connector in the PDC and the PCM harness connector. Is the resistance below 5.0 ohms? If no, repair the open O2 Sensor Heater Relay Control circuit. If yes, go to next step.
  4. Measure the resistance between ground and the O2S Heater Relay Control circuit at the O2 Sensor Downstream Heater Relay connector in the PDC. Is the resistance below 100 ohms? If yes, repair the short to ground in the O2 Sensor Heater Relay Control circuit. If no, go to next step.
  5. Measure the resistance across terminals No. 85 and 86 at the O2 Sensor Downstream Relay (component side). Is the resistance above 100 ohms? If yes, replace the O2 Downstream Relay. If no, go to next step.
  6. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
    7. NOTE: Check for contaminants that may have damaged the O2 Sensor such as contaminated fuel, unapproved silicone, oil and coolant.
    WARNING: When the engine is operating, do not stand in a direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing.
  7. The conditions that set the DTC are not present at this time. The following may help in identifying the intermittent condition. With the engine running at normal operating temperature, monitor the DRBIII® parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set. Review the DRBIII® Freeze Frame information. If possible, try to duplicate the conditions under which the DTC was set. Refer to any Technical Service Bulletins (TSB) that may apply. Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals. Were any of the above conditions present? If yes, repair as necessary. If no, test is complete.
scientia non olet · About LEMON Manuals