Circuit Description
In order to control emissions, a catalytic 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 catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalyst's 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).
Replace the entire HO2S 2 assembly. Do not attempt to repair the HO2S 2 if the following conditions exist:
| • | Damaged wiring |
| • | Damaged electrical connectors |
| • | Damaged terminals |
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, P0202, P0203, P0204, P0300, P0335, P0440, P0442, P0446, P0506, P0507, P0601, P0602, or P1441 are not set. |
| • | The air flow is more than 5.5 grams per second. |
| • | The engine coolant temperature (ECT) is more than 40°C (104°F). |
| • | The throttle position (TP) angle is between 5 percent and 50 percent for 4 seconds. |
Conditions For Setting The DTC
HO2S 2 voltage is more than 1042 mV for 50 to 75 seconds.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the malfunction present. |
| • | The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers. |
| • | A history DTC stores. |
| • | The coolant fan turns ON. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
Check 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 2 -- If there is an internal short in the HO2S 2, the HO2S 2 voltage displayed on a scan tool will be more than 1.0 volt. Disconnect the HO2S 2 and connecting a jumper wire between the HO2S 2 low circuit to engine ground. Replace the HO2S 2 if the displayed voltage goes from more than 1000 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 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 |
Replace the entire HO2S 2 assembly. Do not attempt to repair the HO2S 2 if the following conditions exist:
| • | Damaged wiring |
| • | Damaged electrical connectors |
| • | Damaged terminals |
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 de-acceleration fuel cut-off (DFCO), 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 DFCO.
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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Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor, check for rich conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S is defective, or a rich condition exists only on the suspect HO2S cylinder bank.
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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 | Value(s) | Yes | No | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||||||
Is the HO2S voltage fixed more than the value specified? | 994 mV | |||||||||||||||||
3 | This DTC is intermittent. Are any additional DTCs stored? | -- | Go to Diagnostic Aids | |||||||||||||||
4 |
Is the HO2S voltage within the value range specified? | 351 - 551 mV | ||||||||||||||||
The HO2S is detecting a rich exhaust condition or may be contaminated. Check for one of the following conditions:
Repair any of the above or similar engine conditions as necessary. Did you find a problem? | -- | |||||||||||||||||
Is the voltage more than the specified value? | 20 mV | |||||||||||||||||
7 | Repair the short to voltage in the HO2S HIGH signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||||||
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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 . Is the action complete? | -- | -- | ||||||||||||||||
9 |
Important: Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | -- | |||||||||||||||
10 |
Does the scan tool indicate the diagnostic Passed? | -- | ||||||||||||||||
11 | Does the scan tool display any additional undiagnosed DTCs? | -- | System OK |
