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 10 seconds. |
| • | The engine is operating in Closed Loop. |
| • | The throttle position (TP) angle is between 8-50 percent for 3.8 seconds. |
| • | The manifold absolute pressure (MAP) is greater than 25 kPa. |
Conditions For Setting The DTC
The voltage reading on HO2S 2 remains below 43 mV for 150 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
| • | The exhaust system--Inspect the exhaust system for the following conditions: |
| - | Exhaust system leaks between the TWC converter and the flange |
| - | Exhaust system corrosion between the TWC converter and the flange |
| - | Exhaust system hardware that is loose or missing between the TWC converter and the flange |
| - | Repair the conditions as necessary. |
| • | A faulty electrical connection or a damaged harness--Inspect the harness for a short to ground in the HO2S 2 high signal circuit. Ensure that the HO2S 2 pigtail is not contacting the exhaust. |
| Inspect for the following conditions: |
| - | Wiring contacting the exhaust system |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed harness connectors |
| - | Damaged terminals |
| - | Faulty terminal-to-wire connections |
| - | A damaged harness |
| • | An intermittent test--Observe the HO2S 2 on the scan tool while moving any of the related electrical connectors and the wiring harness with the ignition ON. If the malfunction is induced, the HO2S 2 display will change. This should help isolate the location of the malfunction. |
An intermittent could be the result of the following conditions:
| • | A faulty electrical connection |
| • | Rubbed-through wire insulation |
| • | A broken wire inside the insulation |
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.
Test Description
The number below refer to the step number on the diagnostic table.
Step | Action | Values | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||
Does the HO2S voltage measure less than the value specified? | 26 mV | Go to Step 4 | Go to Step 3 | |||||||||||||
3 | This DTC is intermittent. Are any additional DTCs stored? | -- | Go to Diagnostic Aids | |||||||||||||
4 |
Does the voltage measure within the specified value? | 351-551 mV | Go to Step 5 | Go to Step 6 | ||||||||||||
5 | The HO2S may be detecting a lean exhaust condition. Inspect for one of the following conditions:
Repair any of the above or similar engine conditions as necessary. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 7 | ||||||||||||
6 | Test the high signal circuit of the HO2S for a short to ground or a short to the low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 | ||||||||||||
7 | Inspect for poor connections at the harness connector of the HO2S sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 | ||||||||||||
8 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- | ||||||||||||
9 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- | ||||||||||||
10 |
Does the DTC run and pass? | -- | Go to Step 11 | Go to Step 2 | ||||||||||||
11 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||
