Page 1033 of 5267
P0155-O2 SENSOR 2/1 HEATER PERFORMANCE
For a complete wiring diagramRefer to Section 8W.
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 1035 of 5267

3.(K199) O2 2/1 HEATER CONTROL CIRCUIT OPEN
Disconnect the C3 PCM harness connector.
Measure the resistance of the (K199) O2 2/1 Heater Control circuit from
the O2 harness connector to the PCM harness connector.
Is the resistance below 5 ohmS?
Ye s>>
Go To 4
No>>
Repair the excessive resistance in the (K199) O2 2/1
Heater Control circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
4.(K343) O2 2/1 FUSED ASD RELAY OUTPUT CIRCUIT OPEN
Measure the resistance of the (K343) O2 2/1 Fused ASD Relay Output circuit,from the relay terminal to the O2
Sensor harness connector.
Is the resistance below 5 ohms?
Ye s>>
Go To 5
No>>
Repair the excessive resistance in the (K343) O2 2/1 Fused ASD relay outputcircuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
5.(K343) O2 2/1 FUSED ASD RELAY OUTPUT CIRCUIT SHORTED TO GROUND
Measure the resistance between ground and the (K343) O2 2/1 Fused
ASD Relay Output circuit in the O2 Sensor harness connector.
Is the resistance below 5 ohms?
Ye s>>
Repair the short to ground in the (K343) O2 2/1 Fused ASD
Relay Output circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 6
Page 1036 of 5267
6.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 1037 of 5267
P0157-O2 SENSOR 2/2 CIRCUIT VOLTAGE TOO LOW
For a complete wiring diagramRefer to Section 8W.
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
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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 1040 of 5267
6.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)