2000 Jeep Cherokee Limited, 2D PickupFACTORY OEM SERVICE PROCEDURE

DTC P0135: 1/1 O2 Sensor Heater Failure: Testing

NOTE: 1/1 HO2S may also be referred to as an upstream oxygen sensor. On 2.5L and 4.0L Federal models, 1/1 HO2S is located in exhaust downpipe in front of catalytic converter. On 4.0L Calif. models, 1/1 HO2S is located in front exhaust manifold.
  1. Using scan tool, read 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  3 .
  2. Turn ignition on, with engine off. Using scan tool in SENSOR mode, monitor 1/1 HO2S voltage until voltage stabilizes between .4 and .6 volt (about 3 minutes). Using scan tool, actuate HO2S HEATER TEST and monitor 1/1 HO2S voltage for 3 minutes. If voltage is one volt or less, go to next step. If voltage is more than one volt, go to step  4 .
  3. At this time, conditions for 1/1 HO2S heater failure do not exist or fault is an intermittent problem. Using scan tool, read FREEZE FRAME data while attempting to duplicate the condition that caused DTC to be set by paying special attention to the conditions that 1/1 HO2S heater is monitored. 1/1 HO2S heater is monitored when ignition is off and then engine has cooled down. Recheck for DTCs. If DTC P0135: 1/1 O2S HEATER FAILURE is present, go to next step. If DTC P0135: 1/1 O2S HEATER FAILURE is not present, no problem is indicated at this time. Test is complete.
  4. Turn ignition off. Disconnect 1/1 HO2S connector. Visually inspect connector for corroded, damaged, pushed-out or miswired terminals. Repair connector as necessary. If connector is okay, go to next step.
  5. Turn ignition on, with engine off. Ensure 1/1 HO2S is still disconnected. Using scan tool, actuate HO2S HEATER TEST. Measure voltage between ground and Dark Green/White wire (2.5L) or Dark Green wire (4.0L) at 1/1 HO2S harness connector. If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, repair open in appropriate power circuit to 1/1 HO2S heater. See WIRING DIAGRAMS article.
  6. Ensure 1/1 HO2S connector is still disconnected. On 2.5L, measure resistance between Dark Green/White wire and Black wire at 1/1 HO2S connector (component side). On 4.0L, measure resistance between Dark Green wire and Black wire at 1/1 HO2S connector (component side). On all models, if resistance is not 4-7 ohms, replace 1/1 HO2S. If resistance is 4-7 ohms, 1/1 HO2S heater element is okay. Go to next step.
  7. Using ohmmeter, measure resistance between ground and Black wire at 1/1 HO2S harness connector. If resistance is less than 5 ohms, replace 1/1 HO2S. If resistance is 5 ohms or more, repair open in Black wire (heater ground circuit). See WIRING DIAGRAMS article.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.