Circuit Description
The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal relative to the oxygen storage capacity of the catalytic converter. The PCM can then determine the ability of the catalytic converter 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
| • | No active MAP DTC's |
| • | No active IAT DTC's |
| • | No active ECT DTC's |
| • | No active TP DTC's |
| • | No active Fuel Trim DTC's |
| • | No active Injector Control DTC's |
| • | No active Misfire DTC's |
| • | No active CKP DTC's |
| • | No active EVAP DTC's |
| • | No active IAC DTC's |
| • | No active PCM Memory DTC's |
| • | The Start-up Engine Coolant Temperature (ECT) less than 40°C (104°F). |
| • | The Start-up Intake Air Temperature (IAT) less than 40°C (104°F). |
| • | Difference between ECT and IAT is less than 7°C (45°F). |
| • | Battery voltage is between 11.6 volts and 16 volts. |
| • | The average air flow prior to activity is less than 20 gps. |
Conditions for Setting the DTC
HO2S 2 voltage increases or decreases less than 148 mV from bias voltage in 100 to 190 seconds after a cold start.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles. |
| • | The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records. |
Conditions for Clearing the MIL or DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order to clear the DTCs. |
Diagnostic Aids
Replace the entire HO2S 2 assembly. Do not attempt to repair the HO2S 2 if the following conditions exist:
| • | Damaged HO2S sensor harness wiring |
| • | Damaged electrical connector |
| • | Damaged terminals |
Obstruction of the air reference and degrade 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.
An intermittent may be caused by any of the following conditions:
| • | A poor connection |
| • | Rubbed through wire insulation |
| • | A broken wire inside the insulation |
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The number(s) below refer to the step number(s) 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 (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 diagnosis. The Ignition must remain OFF for at least one half hour before proceeding with 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 (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: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |||||||||
14 |
Important: The HO2S must be cool before proceeding with diagnosis. The Ignition must remain OFF for at least one half hour before proceeding with 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? | -- | Go to the applicable DTC table | System OK |
