Page 1034 of 5267

When Monitored:
With battery voltage greater than 9 volts, at a cold start, ECT less than 147°F, battery temperature sensor
equal to or less than 27°F, and engine at idle for at least 12 seconds.
Set Condition:
O2 sensor voltage greater than 3 volts for 30 to 90 seconds.
Possible Causes
(K199) O2 2/1 HEATER CONTROL CIRCUIT OPEN
(K199) O2 2/1 HEATER CONTROL CIRCUIT SHORTED TO GROUND
(K343) O2 FUSED ASD RELAY OUTPUT CIRCUIT OPEN
(K343) O2 FUSED ASD RELAY OUTPUT CIRCUIT SHORTED TO GROUND
O2 SENSOR
PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
Diagnostic Test
1.O2 SENSOR HEATER OPERATION
Turn the ignition off.
NOTE: Wait a minimum of 8 minutes to allow the O2 Sensor to cool down before continuing the test. Allow
the O2 Sensor voltage to stabilize between 4.6 and 5.0 volts.
Ignition on, engine not running.
With a scan tool, actuate the O2 Heater Test.
With the scan tool, monitor 2/1 O2 Sensor voltage for at least 2 minutes.
Does the voltage stay above 4.5 volts?
Ye s>>
Go To 2
No>>
Refer to the INTERMITTENT CONDITION Symptom. (Refer to 9 - ENGINE - DIAGNOSIS AND TEST-
ING)
2.O2 SENSOR HEATER ELEMENT
Turn the ignition off.
NOTE: Allow the O2 sensor to cool down to room temperature.
Disconnect the O2 Sensor harness connector.
Measure the resistance of the O2 Heater Element across the 2/1 O2 Sensor connector between the (K199) O2
Heater Control terminal and the (K343) Fused ASD relay output terminal.
NOTE: O2 Heater Element resistance values should be measured at 70°F (21.1°C). The resistance value will
vary with different temperature values.
Is the resistance of the O2 Sensor Heater Element between 3.3 and 4.1 ohms?
Ye s>>
Go To 3
No>>
Replace the O2 Sensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
Page 1038 of 5267

When Monitored:
At a cold start, engine coolant below 98°F, Ambient/Battery Sensor readingwithin27°F,andEngineCoolant
Temperature above 170°F on the previous key off.
Set Condition:
The Oxygen Sensor signal voltage is below 0.156 of a volt for 28 seconds after starting engine.
Possible Causes
(K243) O2 SENSOR 2/2 SIGNAL CIRCUIT SHORTED TO GROUND
(K243) O2 SENSOR 2/2 SIGNAL CIRCUIT SHORTED TO (K900) SENSOR GROUND CIRCUIT
(K243) O2 SENSOR 2/2 SIGNAL SHORTED TO THE (Z1) HEATER GROUND CIRCUIT
O2 SENSOR
PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
Diagnostic Test
1.O2 SENSOR BELOW 0.16 OF A VOLT
Ignition on, engine not running.
With the scan tool, read DTCs and record the related Freeze Frame data.
Start the engine.
Allow the engine to idle for 4 to 5 minutes.
With the scan tool, read the O2 Sensor voltage.
Is the voltage below 0.16 of a volt?
Ye s>>
Go To 2
No>>
Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
2.O2 SENSOR OPERATION
WARNING: When the engine is operating, do not stand in a direct line with thefan. Do not put your hands
near the pulleys, belts, or fan. Do not wear loose clothing.
Disconnect the O2 Sensor harness connector.
Start the engine.
With the scan tool, monitor the O2 Sensor voltage.
IstheO2Sensorvoltageabove0.16ofavolt?
Ye s>>
Replace the O2 Sensor
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 3
Page 1039 of 5267

3.(K243) O2 SENSOR 2/2 SIGNAL CIRCUIT SHORTED TO GROUND
Turn the ignition off.
Disconnect the PCM harness connectors.
Measure the resistance between ground and the (K243) O2 Sensor 2/2
Signal circuit at the 2/2 O2 Sensor harness connector.
Istheresistancebelow100ohms?
Ye s>>
Repair the short to ground in the (K243) O2 Sensor 2/2 Sig-
nal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 4
4.(K243) O2 SENSOR 2/2 SIGNAL CIRCUIT SHORTED TO (K900) SENSOR GROUND CIRCUIT
Measure the resistance between the (K243) O2 Sensor 2/2 Signal cir-
cuit and the (K900) Sensor ground circuit at the O2 Sensor harness
connector.
Istheresistancebelow100ohms?
Ye s>>
Repair the short between the (K900) Sensor ground circuit
and the (K243) O2 Sensor 2/2 Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 5
5.(K243) O2 SENSOR 2/2 SIGNAL CIRCUIT SHORTED TO (Z1) HEATER GROUND CIRCUIT
Measure the resistance between the (K243) O2 Sensor 2/2 Signal cir-
cuit and the (Z1) O2 Sensor Heater ground circuit if it applies to the O2
Sensor being tested.
Istheresistancebelow100ohms?
Ye s>>
Repair the short between the (K243) O2 Sensor 2/2 Signal
circuit and the (Z1) Heater ground circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 6
Page 1042 of 5267

When Monitored:
With battery voltage greater than 10.4 volts, engine running for more than4 minutes and coolant temperature
above 180°F.
Set Condition:
The oxygen sensor voltage is above 1.5 volts.
Possible Causes
(K243) O2 SENSOR 2/2 SIGNAL SHORTED TO VOLTAGE
(K243) O2 SENSOR 2/2 SIGNAL CIRCUIT OPEN
(K243) O2 SENSOR 2/2 SIGNAL CIRCUIT SHORTED TO THE (K344) O2 HEATER RELALY OUPUT CIRCUIT
(K900) SENSOR GROUND CIRCUIT OPEN
(Z1) O2 SENSOR HEATER GROUND CIRCUIT OPEN
O2 SENSOR
PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
Diagnostic Test
1.O2 SENSOR ABOVE 1.5 VOLTS
Ignition on, engine not running.
With the scan tool, read DTCs and record the related Freeze Frame data.
Start the engine.
Allow the engine to idle for 4 to 5 minutes.
With the scan tool, read the O2 Sensor voltage.
Is the voltage above 1.5 volts?
Ye s>>
Go To 2
No>>
Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
2.O2 SENSOR OPERATION
WARNING: When the engine is operatind, do not stand in a direct line with thefan. Do not put your hands
near the pulleys, belts, or fan. Do not wear loose clothing.
Turn the ignition off.
Disconnect the O2 Sensor harness connector.
Start the engine.
With the scan tool, monitor the O2 Sensor voltage.
Is the O2 Sensor voltage below 1.5 volts?
Ye s>>
Replace the O2 Sensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 3
Page 1043 of 5267
3.(K243) O2 SENSOR 2/2 SIGNAL CIRCUIT SHORTED TO VOLTAGE
Turn the ignition off.
Disconnect the PCM harness connectors.
Ignition on, engine not running.
Using a 12-volt test light connected to ground, probe the (K243) O2
Sensor 2/2 Signal circuit at the 2/2 O2 Sensor harness connector.
Does the test light illuminate brightly?
Ye s>>
Repair the short to voltage in the (K243) O2 Sensor 2/2
Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 4
4.(K243) O2 SENSOR 2/2 SIGNAL CIRCUIT OPEN
Turn the ignition off.
Measure the resistance of the (K243) O2 Sensor 2/2 Signal circuit from
the 2/2 O2 Sensor harness connector to the PCM harness connector.
Is the resistance below 5.0 ohms?
Ye s>>
Go To 5
No>>
Repair the open in the (K243) O2 Sensor 2/2 Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
Page 1045 of 5267

7.(K344) O2 SENSOR HEATER RELAY OUTPUT CIRCUIT OPEN
Connect the PCM harness connectors.
Ignition on, engine not running.
With the scan tool actuate the O2 Heater Test.
Measure the voltage on the (K344) O2 Sensor Heater Relay Output cir-
cuit.
Is the voltage above 11.0 volts?
No>>
Repair the open in the (K344) O2 Sensor Heater Relay Out-
put circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
Ye s>>
Go To 8
8.(Z1) O2 SENSOR HEATER GROUND CIRCUIT OPEN
Turn the ignition off.
Disconnect the PCM harness connectors.
Measure the resistance between ground and the (Z1) O2 Sensor Heater
ground circuit from the 2/2 O2 Sensor harness connector.
Is the resistance below 5.0 ohms?
Ye s>>
Go To 9
No>>
Repair the open in the (Z1) O2 Sensor Heater ground cir-
cuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
9.PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal
push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and
Ground circuits.
Were there any problems found?
Ye s>>
Repair as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No>>
Replace and program the Powertrain Control Module per Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
Page 1047 of 5267

When Monitored:
Start engine. Allow engine to idle. For 1st part of test, if limits are exceeded, test passes. If not, 2nd part of
test runs. amb/batt temp >44°F, Baro >22.13
H2O, battery >10.5 volts, MAP >11.79 & <18.15H2O, RPM
>1350 & <2200 and vss >50 and <65.
Set Condition:
The oxygen sensor signal voltage is switching from below 0.39 of a volt to above 0.58 of a volt and back fewer
times than required.
Possible Causes
EXHAUST LEAK
(K243) O2 2/2 SIGNAL CIRCUIT
(K900) SENSOR GROUND 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 forthe remaining O2 Sensors.
With a scan tool, read DTCs.
Is the DTC active at this time?
Ye s>>
Go To 2
No>>
Refer to the INTERMITTENT CONDITION Symptom. (Refer to 9 - ENGINE - STANDARD PROCE-
DURE)
2.EXHAUST LEAK
Start the engine.
Inspect the exhaust system for leaks between the engine and the O2 Sensors.
Are there any exhaust leaks?
Ye s>>
Repair or replace the leaking exhaust parts as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 3
3.(K243) O2 2/2 SIGNAL CIRCUIT VOLTAGE DROP
Turn the ignition off
Ignition on, engine not running.
With a voltmeter, back probe the (K243) O2 Sensor Signal circuit at the 2/2 O2 Sensor harness connector and the
PCM harness connector.
NOTE: Make sure the voltmeter leads meet the terminals in the connector andthat there is good terminal to
wire connection and are connected for positive polarity.
Start the engine.
Page 1048 of 5267

Allow the engine to idle.
Is the voltage below 0.10 of a volt?
Ye s>>
Go To 4
No>>
Repair the excessive resistance in the (K243) O2 Sensor 2/2 Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
4.(K900) SENSOR GROUND CIRCUIT VOLTAGE DROP
Turn the ignition off.
With a voltmeter, back probe the (K900) Sensor ground circuit at the 2/2 O2 Sensor harness connector and PCM
harness connector.
NOTE: Make sure the voltmeter leads meet the terminals in the connector andthat there is good terminal to
wire connection.
Start the engine.
Allow the engine to idle.
Is the voltage below 0.10 of a volt?
Ye s>>
Go To 5
NOTE: Turn the ignition off before continuing.
No>>
Repair the excessive resistance in the (K900) Sensor ground circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
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)