Circuit Description
In order to control emissions, a 3-way catalytic (TWC) converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.
The powertrain control module (PCM) has the capability to monitor this process by using a rear heated oxygen sensor (HO2S) 2. The HO2S 2, located in the exhaust stream past the TWC converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor (O2S) 1.
Obstruction of the air reference and degraded HO2S 2 performance could result from any attempt to repair the above conditions.
The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.
Conditions for Running the DTC
| • | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0201-P0204, P0300, P0301-P0304, P0335, P0440, P0442, P0446, P0506, P0507, P0601, P0602, or P1441 are not set. |
| • | The engine coolant temperature (ECT) is greater than 70°C (158°F). |
| • | The battery voltage is greater than 10 volts. |
| • | The fuel level is greater than 10 percent. |
| • | The engine run time is greater than 30 seconds. |
| • | The air flow is more than 5.5 g/s. |
| • | The throttle position (TP) is between 8-56 percent. |
| • | The manifold absolute pressure (MAP) is greater than 25 kPa. |
| • | The engine is operating in Closed Loop. |
Conditions For Setting The DTC
The HO2S 2 remains between 425-460 mV for 125 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
An intermittent could be the result of the following conditions:
| • | A faulty electrical connection |
| • | Moisture in the electrical connector or connector wiring |
| • | Rubbed-through wire insulation |
| • | A broken wire inside the insulation |
Inspect for the following conditions:
| • | A faulty electrical connection or a damaged harness--Inspect the PCM harness for an open in the HO2S 2 signal circuit. Inspect for the following conditions: |
| - | Improper mating |
| - | Broken locks |
| - | Improperly-formed connectors |
| - | Damaged terminals |
| - | A faulty terminal-to-wire connection |
| - | A damaged harness |
| • | An intermittent test--Observe the HO2S 2 on the scan tool while moving the related electrical connectors and the wiring harness with the ignition switch ON. If the malfunction is induced, the HO2S 2 display will change. This test should help isolate the location of the malfunction. |
Obstruction of the air reference and degraded HO2S 2 performance could result in any attempt to repair the above conditions.
The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.
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.
-
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 . 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 | |
