Refer to Engine Controls Schematics
Cell 20: Engine Data Sensors-HO2S 1 and HO2S 2
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Circuit Description
The PCM monitors the Heated Oxygen Sensor (HO2S) activity for 100 seconds. During this test period the PCM counts the number of times that the HO2S signal voltage crosses the rich to lean and lean to rich thresholds. If the PCM determines that the HO2S did not switch enough times, DTC P1133 will be set.
A lean to rich switch is determined when the HO2S voltage changes from less than 300 mV to greater than 600 mV. A rich to lean switch is determined when the HO2S voltage changes from more than 600 mV to less than 300 mV.
Conditions for Running the DTC
| • | No active MAF, TP, IAT, MAP, ECT, EGR sensor, injector circuit, EVAP, fuel trim, or HO2S heater DTCs. |
| • | Above conditions present for a 100 second monitoring period after closed loop. |
| • | Mass Air Flow is between 10 and 30 g/s. |
| • | ECT is greater than 50°C (122°F). |
| • | Engine speed is between 1000 and 3000 RPM. |
Conditions for Setting the DTC
| • | The PCM monitors fewer than 40 rich to lean and 40 lean to rich switches for HO2S 1. |
| • | The condition is present for a 100 second monitoring period. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. |
| • | The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Inspect for the following:
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Poor terminal connection. |
| Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Intermittents and Poor Connections Diagnosis , and Connector Repairs Wiring Systems. |
| • | Damaged harness. |
| Inspect the wiring harness for damage. If the harness appears to be OK, observe the sensor display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the sensor display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems. |
| • | Inspect the PCM and the engine grounds for clean and secure connections. |
If the DTC is determined to be intermittent, reviewing the Fail Records can be useful in determining when the DTC was last set.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table:
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This step Tests for conditions which may cause the heated oxygen sensor to appear faulty. Correct any of the described conditions if present.
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Before replacing the HO2S, Test for silicon contamination. Refer to
Notice: Contamination of the oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption. Remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream in order to check for contamination. If contaminated, the portion of the sensor exposed to the exhaust stream will have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Eliminate the source of contamination before replacing the oxygen sensor.
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Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain OBD System Check performed? | -- | ||||||||||
2 |
Important: : If any DTCs are set (except P1133 or P1134), go to those DTCs before proceeding with this diagnostic table.
Note the test result, does the scan tool indicate DTC failed this ignition? | -- | Go to Diagnostic Aids | |||||||||
3 |
Was a problem found? | -- | ||||||||||
Visually/physically inspect the following items:
Was a problem found in any of the above areas? | -- | |||||||||||
5 |
Does the scan tool indicate voltage near the specified value? | 450mV | ||||||||||
6 |
Does the scan tool indicate voltage less than the specified value? | 300mV | ||||||||||
Replace the affected Heated Oxygen Sensor(s). Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | ||||||||||
8 | Repair the condition as necessary. Refer to Testing for Continuity Intermittents and Poor Connections Diagnosis Repairing Connector Terminals and Connector Repairs . Is the action complete? | -- | -- | |||||||||
9 | Repair open HO2S 1 low signal circuit or grounded HO2S 1 high signal circuit. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | |||||||||
10 | Repair open HO2S 1 high signal circuit or faulty PCM connections. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | |||||||||||
11 |
Note the test result, does the scan tool indicate DTC failed this ignition? | -- | System OK |
