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
| • | The engine coolant temperature (ECT) is less than 40°C (104°F). |
| • | The intake air temperature (IAT) is less than 40°C (104°F). |
| • | The difference between the ECT and the IAT is less than 7°C (45°F). |
| • | The throttle position (TP) is less than 18 percent. |
Conditions for Setting the DTC
HO2S 2 voltage increases less than 150 mV in 100 to 190 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
An intermittent could be the result of the following conditions:
| • | A faulty electrical connection |
| • | Moisture in the connector/wiring |
| • | Rubbed-through wire insulation |
| • | A broken wire inside the insulation |
Check for a faulty electrical connection or a damaged harness. Inspect the harness electrical connectors for the following conditions:
| • | Improper mating |
| • | Broken locks |
| • | Improperly-formed electrical connectors |
| • | Damaged terminals |
| • | A faulty terminal-to-wire connection |
| • | A damaged harness |
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 numbers on the Diagnostic Table.
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As the heater warms the oxygen sensor to operating temperature, the HO2S will output a voltage in relation to the amount of oxygen in the exhaust. With the ignition ON and the engine OFF, the exhaust usually contains a high oxygen content. With the engine OFF the HO2S voltage will usually decrease from the initial, or bias, voltage due to the high oxygen content.
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This step checks for proper HO2S heater ignition positive voltage and ground supply.
-
This step checks for proper PCM and signal circuit operation.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||
|
Important: The HO2S must be cool before proceeding with a diagnosis. The Ignition must remain OFF for at least one-half hour before proceeding with a diagnosis.
Does the HO2S voltage increase or decrease from the initial voltage by at least the value specified? | 150 mV | |||||||||||
3 | The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:
Repair any of the above conditions as necessary. Refer to Wiring Repairs or Connector Repairs in Wiring Systems. Did you find a problem? | -- | Go to Diagnostic Aids | |||||||||
Is the test lamp ON? | -- | |||||||||||
Ensure the ignition is ON while the engine is OFF. Is the HO2S voltage less than the specified value? | 20 mV | |||||||||||
6 | Connect the test lamp between the HO2S heater ignition positive voltage circuit terminal at the engine harness side and a known good ground. Ensure the ignition is ON while the engine is OFF. Is the test lamp ON? | -- | ||||||||||
7 |
Is the resistance less than the specified value? | 5 ohms | ||||||||||
8 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | |||||||||
9 | Repair the open HO2S heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
10 | Repair the lack of voltage on the HO2S heater ignition positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. If the fuse is blown, repair the short to ground on the circuit. A blown fuse or lack of voltage to the fuse may cause other DTCs or symptoms to be present. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
11 | Repair the circuit that measured high resistance. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
12 |
Did you find a problem? | -- | ||||||||||
13 |
Important: Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the repair? | -- | -- | |||||||||
14 |
Important: The HO2S must be cool before proceeding with a diagnosis. The Ignition must remain OFF for at least one-half hour before proceeding with a diagnosis.
Does the HO2S voltage increase or decrease from the initial voltage by at least the value specified? | 150 mV | ||||||||||
15 | Does the scan tool display any additional undiagnosed DTCs? | -- | System OK |
