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Home >> Jeep >> 2000 >> Grand Cherokee Laredo, 4.0 S, AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0159: 2/2 O2 Sensor Slow Response (With CALIF. Emissions) >> Testing

DTC P0159: 2/2 O2 Sensor Slow Response (With CALIF. Emissions): Testing

NOTE: 2/2 HO2S may also be referred to as a downstream oxygen sensor. On 4.0L, 2/2 HO2S is located in rear exhaust pipe below front mini-catalytic converter. On 4.7L, 2/2 HO2S is located in exhaust pipe behind right (passenger's side) catalytic converter.
  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  10 .
  2. Using scan tool, actuate O2 HEATER TEST and monitor HO2S signal voltage. Voltage should change to less than 1.5 volts within 2-3 minutes. If voltage is as specified, go to next step. If voltage is not as specified, go to step  7 .
  3. Start engine and allow it to idle. Check exhaust system for leaks between engine and 2/2 HO2S. Repair exhaust system leaks as necessary. If exhaust system is okay, go to next step.
  4. Turn ignition off. Using voltmeter, backprobe Black/Light Blue wire between 2/2 HO2S and terminal No. 4 at PCM C1 connector. Start engine and allow it to idle. Ensure coolant temperature is at normal operating temperature. Note voltage reading. If voltage drop is less than .1 volt, go to next step. If voltage drop is .1 volt or more, repair poor connection causing high resistance on 2/2 HO2S ground circuit (Black/Light Blue wire) between 2/2 HO2S and PCM.
  5. Turn engine off. Using a voltmeter, backprobe Pink/White wire between 2/2 HO2S connector and terminal No. 29 at PCM C1 connector. See Figure . Start engine and allow it to idle. Ensure coolant temperature is at normal operating temperature. Note voltage reading. If voltage drop is less than .1 volt, go to next step. If voltage drop is .1 volt or more, repair poor connection causing high resistance on 2/2 HO2S signal circuit (Pink/White wire) between 2/2 HO2S and PCM.
  6. At this time, 2/2 HO2S is assumed to be defective. Replace 2/2 HO2S.
  7. Turn ignition off. Disconnect 2/2 HO2S connector. Turn ignition on. Using scan tool, actuate O2S HEATER TEST. Measure voltage between ground and Violet/Orange wire at 2/2 HO2S harness connector. If voltage is more than 11 volts, go to next step. If voltage is 11 volts or less, repair open in Violet/Orange wire.
  8. Turn ignition off. Measure resistance between ground and Black wire at 2/2 HO2S harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Black wire between ground and 2/2 HO2S.
  9. At this time, 2/2 HO2S is assumed to be defective. Replace 2/2 HO2S.
  10. Start engine and allow it to idle. Check exhaust system for leaks between engine and 2/2 HO2S. Repair exhaust system leaks as necessary. If exhaust system is okay, go to next step.
  11. Turn ignition off. Visually inspect related connectors and wiring harness for damage. Repair connectors and wiring harness as necessary. If connectors and wiring harness are okay, reconnect all connectors. Start engine. Wiggle 2/2 HO2S connector and wiring harness while monitoring scan tool display. If GOOD TRIP counter display count changes to "0", repair connector or wiring harness where wiggling caused display to change. If GOOD TRIP counter display count does not change to "0", no problem is indicated at this time. Check for any related technical service bulletins that may apply.
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