Circuit Description
The heated oxygen sensor (HO2S 2), located in the exhaust stream past the catalytic converter, produces an output signal relative to the oxygen storage capacity of the catalytic converter. The powertrain control module (PCM) can then determine the ability of the catalytic converter to convert the exhaust emissions effectively. The HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor 1 (O2S 1).
Conditions for Running the DTC
| • | No active MAP DTCs |
| • | No active IAT DTCs |
| • | No active ECT DTCs |
| • | No active TP DTCs |
| • | No active fuel trim DTCs |
| • | No active injector control DTCs |
| • | No active misfire DTCs |
| • | No active CKP DTCs |
| • | No active EVAP DTCs |
| • | No active IAC DTCs |
| • | No active PCM memory DTCs |
| • | Air flow is more than 5.5 grams per second |
| • | Engine coolant temperature (ECT) is more than 40°C (104°F) |
| • | The above conditions are met for 140 seconds |
| • | Throttle position (TP) is between 4 percent and 56 percent |
Conditions For Setting The DTC
HO2S 2 remains between 425 mV and 460 mV for 125 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles. |
| • | The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tools Freeze Frame and Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
Whenever the oxygen sensor pigtail wiring, the connector, or the terminal are damaged, replace the entire oxygen sensor assembly. Do not attempt to repair the wiring, connector, or terminals. In order for the sensor to function properly, the rear HO2S 2 must have a clean air reference. This clean air reference is obtained by way of the oxygen sensor wires. Any attempt to repair the wires, connectors, or terminals may result in the obstruction of the air reference and degrade the performance of the oxygen sensor.
A poor connection, rubbed through wire insulation or a wire broken inside the insulation may cause an intermittent.
Check for the following conditions:
| • | A poor connection or damaged harness -- Inspect the PCM harness for the following conditions: |
| - | Open in the rear HO2S high circuit |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wire connection |
| - | Damaged harness. |
| • | An intermittent test -- Observe the rear HO2S 2 on the scan tool while moving the related connectors and wiring harness with the key ON. Whenever the fault is induced, the rear HO2S 2 display will change. This may help isolate the location of the malfunction. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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After the ignition is turned ON, the HO2S heater heats up causing the HO2S signal voltage to either increase or decrease. This indicates that the HO2S heater is OK.
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If the HO2S voltage changes more than the specified value, the condition is not present.
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If the voltage is below the specified value, the high signal circuit, the low signal circuit, and the PCM are OK.
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If the voltage is above the specified value, the low signal circuit is OK.
-
Resistance below the specified value indicates the HO2S heater is shorted.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
|
Important: Allow the engine to cool for one-half hour before proceeding with this diagnostic. This allows the HO2S signal voltage to return to bias voltage, approximately 447 mV.
Does the HO2S 2 voltage change from bias voltage to more than or less than the specified range? | 300-600 mV | Go to Step 3 | Go to Step 5 | |
Did the HO2S 2 voltage change more than the specified value? | 300 mV | Go to Step 4 | Go to Step 5 | |
4 |
Did the DTC fail this ignition? | -- | Go to Step 5 | Go to Diagnostic Aids |
Is the HO2S 2 voltage less than the specified value? | 200 mV | Go to Step 9 | Go to Step 6 | |
Is the voltage more than the specified value? | 4 V | Go to Step 7 | Go to Step 8 | |
7 | Test the HO2S 2 high signal circuit for an open. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 16 |
8 | Test the HO2S 2 low signal circuit for an open. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 16 |
9 |
Is the fuse open? | -- | Go to Step 12 | Go to Step 10 |
10 |
Does the test lamp illuminate? | -- | Go to Step 11 | Go to Step 17 |
11 | Connect a test lamp between the ignition voltage circuit of the HO2S 2 on the engine harness side and the heater ground circuit of the HO2S 2 on the engine harness side. Does the test lamp illuminate? | -- | Go to Step 15 | Go to Step 18 |
12 |
Did you find and correct a short to ground in the ignition voltage circuit? | -- | Go to Step 21 | Go to Step 13 |
13 | Test the HO2S 2 ignition voltage circuit, sensor side, for a short to the HO2S Body. Refer to Testing for Continuity in Wiring Systems. Did you find the condition? | -- | Go to Step 19 | Go to Step 14 |
Measure the resistance between the HO2S 2 ignition voltage circuit, sensor side, and the HO2S 2 heater ground circuit, sensor side with a DMM. Does the resistance measure below the specified value? | 3 ohms | Go to Step 19 | Go to Diagnostic Aids | |
15 | Inspect for poor connections at the harness connector of the HO2S 2. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 19 |
16 | Inspect for poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 20 |
17 | Repair the open in the HO2S 2 ignition voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 21 | -- |
18 | Repair the open in the HO2S 2 heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 21 | -- |
19 | Replace the HO2S 2. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 21 | -- |
20 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | Go to Step 21 | -- |
21 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 22 |
22 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
