Note. For connector terminal identification, see CONNECTOR IDENTIFICATION . For circuit identification and wiring diagram, see CHEROKEE wiring diagram in WIRING DIAGRAMS article.
Note. DTC P0138: 1/2 O2S SHORTED TO VOLTAGE is monitored with engine running for more than 2 minutes and engine coolant temperature at more than 170°F (76.7°C). DTC may be stored in Powertrain Control Module (PCM) when PCM senses that 1/2 Heated Oxygen Sensor (HO2S) voltage is more than 1.2 volts. Possible causes are: defective 1/2 HO2S, defective PCM, defective connectors or defective wiring.
Note. 1/2 HO2S is located in downstream position.
- Start engine and warm to temperature more than 170°F (76.7°C). Leave engine running for 5 minutes. Using scan tool, read 1/2 HO2S voltage. If voltage is more than 4.97 volts, go to next step. If voltage is 4.97 volts or less, go to step 4).
- Turn ignition off. Disconnect 1/2 HO2S connector. Clean and/or repair connector as necessary. Start engine and allow it to idle for at least 5 minutes. Using scan tool, read 1/2 HO2S voltage. If voltage is 4.97 volts or less, go to next step. If voltage is more than 4.97 volts, repair 1/2 HO2S signal circuit (Tan/White wire) for short to voltage. Perform TEST VER-5A.
- At this time, 1/2 HO2S is assumed to be defective. Replace 1/2 HO2S. Perform TEST VER-5A.
- Turn engine off. Start engine and allow it to idle. Using scan tool, read and monitor 1/2 HO2S voltage while wiggling 1/2 HO2S connector and wiring harness. If voltage is 1.2 volts or less at any time, go to next step. If voltage is more than 1.2 volts at any time, repair intermittent short to voltage in wiring harness. Perform TEST VER-5A.
- Turn ignition off. Disconnect 1/2 HO2S connector. Clean and/or repair connector as necessary. Visually inspect related connectors and wiring harness for damage. Repair connectors and wiring harness as necessary. Perform TEST VER-5A. If connectors and wiring harness are okay, test is complete.