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
HO2S 2 voltage is more than 1,042 mV for 50-75 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
Inspect for the following conditions:
| • | A rich exhaust--An overly rich exhaust may load the catalyst, causing high HO2S 2 signal voltages. |
| • | Silicone contamination--Silicone contamination of HO2S 2 could cause a false rich condition . A powdery white deposit on the sensor will indicate this condition. |
| • | A malfunctioning HO2S--If there is an internal short in the HO2S 2, the HO2S 2 voltage displayed on a scan tool will be more than 1 volt. Disconnect the HO2S 2 and connect a jumper wire between the HO2S 2 low signal circuit to engine ground. Replace the HO2S 2 if the displayed voltage goes from more than 1,000 mV to approximately 450 mV . |
| • | 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 turned ON. If the malfunction is induced, the HO2S 2 display will change. This should help to isolate the location of the malfunction. |
| • | Damaged harness--Inspect PCM harness for a short to voltage in the HO2S 2 high signal circuit. |
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 numbers below refer to the step number on the diagnostic table.
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In order to determine if the engine is rich during decel fuel cut-off (DFCO) mode, operate the vehicle up to highway speed conditions, and release the accelerator pedal, allowing the vehicle to coast in gear. Monitor the scan tool HO2S voltage and the DFCO parameter. A rich condition will cause the HO2S voltage to be more than 468 mV during the DFCO mode.
An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of unapproved silicon room-temperature vulcanizing (RTV) engine gasket material or the use of silicon-based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also become contaminated.
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This step checks the HO2S high signal circuit for a short to voltage.
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An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of unapproved silicon RTV engine gasket material or the use of silicon-based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also become contaminated.
Step | Action | Values | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||
Is the HO2S voltage fixed more than the value specified? | 994 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 is detecting a rich exhaust condition or may be contaminated. 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 11 | Go to Step 8 | ||||||||||||
Is the voltage more than the specified value? | 20 mV | Go to Step 7 | Go to Step 10 | |||||||||||||
7 | Repair the short to voltage in the HO2S high signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 11 | -- | ||||||||||||
8 | 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 11 | Go to Step 9 | ||||||||||||
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Important: Before replacing a contaminated HO2S, determine and repair the cause of the contamination. Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | |||||||||||||
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||||||
11 |
Does the DTC run and pass? | -- | Go to Step 12 | Go to Step 2 | ||||||||||||
12 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||
