Jeep Liberty KJ. Manual — part 497
P0139-O2 SENSOR 1/2 SLOW RESPONSE
For a complete wiring diagram Refer to Section 8W.
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ENGINE ELECTRICAL DIAGNOSTICS
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Theory of Operation
The downstream O2 Sensor is located in the exhaust path behind the catalytic converter, is monitored for proper
response to assure optimum catalytic converter efficiency. The downstream O2 response monitor is intended to
diagnose a downstream O2 sensor that is not moving or stuck in a voltage window and to insure accurate infor-
mation for catalyst monitor diagnosis.
•
When Monitored:
Vehicle is started and driven between 20 and 55 MPH with the Throttle open for a minimum of 120 seconds.
Coolant greater than 70°C (158°F). Catalytic Converter Temp greater than 600°C (1112°F) and EVAP Purge is
active.
•
Set Condition:
The oxygen sensor signal voltage switches less than 16 times from lean to rich within 20 seconds during mon-
itoring. Two Trip Fault. Three good trips to turn off the MIL.
Possible Causes
EXHAUST LEAK
(K141) O2 1/2 SIGNAL CIRCUIT
(K904) O2 DOWNSTREAM RETURN CIRCUIT
O2 SENSOR
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
Diagnostic Test
1.
ACTIVE DTC
NOTE: Check for contaminants that may have damaged the O2 Sensor: contaminated fuel, unapproved sil-
icone, oil and coolant.
Ignition on, engine not running.
NOTE: After the repairs have been made, verify proper O2 Sensor operation. If all the O2 Sensor voltage
readings have not returned to normal, follow the diagnostic procedure for the remaining O2 Sensors.
With a scan tool, read DTCs.
Is the DTC active at this time?
Yes
>> Go To 2
No
>> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
2.
EXHAUST LEAK
Start the engine.
Inspect the exhaust system for leaks between the engine and the O2 Sensors.
Are there any exhaust leaks?
Yes
>> Repair or replace the leaking exhaust parts as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
>> Go To 3
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ENGINE ELECTRICAL DIAGNOSTICS
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3.
(K141) O2 1/2 SIGNAL CIRCUIT
Turn the ignition off
Disconnect the 1/2 O2 Sensor harness connector.
Ignition on, engine not running.
Measure the voltage on the (K141) O2 1/2 Signal circuit in the O2 Sen-
sor harness connector.
Is the voltage approximately 5.0 volts?
Yes
>> Go To 4
No
>> Check the (K141) O2 1/2 Signal circuit for a short to
ground, open, or short to voltage. If OK, replace and pro-
gram the Powertrain Control Module per Service Informa-
tion.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
4.
(K904) O2 DOWNSTREAM RETURN CIRCUIT
Measure the voltage on the (K904) O2 Downstream Return circuit in the
1/2 O2 Sensor harness connector.
Is the voltage at 2.5 volts?
Yes
>> Check the (K904) O2 Downstream Return circuit for a short
to ground, open, or short to voltage. If OK, replace and pro-
gram the Powertrain Control Module per Service Informa-
tion.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No
>> Go To 5
5.
O2 SENSOR
If there are no possible causes remaining, view repair.
Repair
Replace the O2 Sensor
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
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ENGINE ELECTRICAL DIAGNOSTICS
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P0141-O2 SENSOR 1/2 HEATER PERFORMANCE
For a complete wiring diagram Refer to Section 8W.
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ENGINE ELECTRICAL DIAGNOSTICS
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