Circuit Description
The heated oxygen sensor 2 (HO2S) 2, located in the exhaust stream past the 3-way catalytic converter (TWC), produces an output signal relative to the oxygen storage capacity of the TWC. The powertrain control module (PCM) can then determine the ability of the TWC to convert the exhaust emissions effectively. The HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor 1 (O2S) 1.
Conditions for Running the DTC
| • | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0169, P0171, P0172, P0178, P0179, P0201-P0204, P0300, P0301-P0304, P0336, P0440, P0446, P0452, P0453, P0506, P0507, P0601, P0602, or P1441 are not set. |
| • | The ignition 1 voltage is greater than 10 volts. |
| • | The engine run time is less than 4.25 minutes. |
| • | The intake air temperature (IAT) is less than 45°C (113°F). |
| • | The start up engine coolant temperature (ECT) and start up IAT are less than 45°C (113°F). |
| • | The difference between ECT and IAT is less than 7°C (45°F). |
| • | The fuel level is greater than 10 percent. |
| • | The HO2S voltage at start up must be between 395-495 mV. |
| • | The fuel ethanol composition is less than 15 percent. |
Conditions for Setting the DTC
The HO2S voltage does not go greater than 600 mV or less than 300 mV within 110-255 seconds after cold start. Depending on driving conditions and start up coolant temperature.
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:
| • | Poor electrical connection |
| • | Moisture in the connectors or wiring |
| • | Rubbed through wire insulation |
| • | Broken wire inside of the insulation |
Inspect for a poor 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 poor 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 connector |
| • | Damaged terminals |
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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As the heater warms the O2S 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.
-
This step checks for proper HO2S heater ignition 1 voltage and ground supply.
-
This step checks for proper PCM and signal circuit operation.
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: 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 | Go to Step 3 | Go to Step 4 | |||||||||
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 and correct the condition? | -- | Go to Step 14 | Go to Diagnostic Aids | ||||||||
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 6 | |||||||||
Is the HO2S voltage less than the specified value? | 20 mV | Go to Step 8 | Go to Step 7 | |||||||||
6 |
Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 10 | ||||||||
7 |
Does the resistance measure less than the specified value? | 5 ohms | Go to Step 12 | Go to Step 11 | ||||||||
8 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||||
9 | Repair the open HO2S heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 14 | -- | ||||||||
10 |
Did you complete the repair? | -- | Go to Step 14 | -- | ||||||||
11 | Repair the circuit that measured high resistance. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 14 | -- | ||||||||
12 |
Did you complete the repair? | -- | Go to Step 14 | Go to Step 13 | ||||||||
13 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||||
14 |
Does the DTC run and pass? | -- | Go to Step 15 | Go to Step 2 | ||||||||
15 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||
