Circuit Description
The powertrain control module (PCM) continuously monitors the oxygen sensor 1 (O2S) 1 activity for 100 seconds. During the monitor period, the PCM counts the number of times that the O2S 1 switches from rich-to-lean and from lean-to-rich. You can determine a total for all of the switches with this information. If the number of switches is too low, a diagnostic trouble code (DTC) P1133 will set.
Conditions For Running The DTC
| • | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0201-P0204, P0300, P0301-P0304, P0335, P0440, P0442, P0446, P0506, P0507, P0601, P0602, or P1441 are not set. |
| • | The engine coolant temperature (ECT) is more than 70°C (158°F). |
| • | The engine speed is between 1,600-2,450 RPM. |
| • | The fuel level is greater than 10 percent. |
| • | The engine is operating in Closed Loop. |
| • | The throttle position (TP) angle is between 9-18 percent. |
| • | The evaporative emissions (EVAP) control system is commanded open for more than 36 percent. |
| • | The purge learned memory is more than approximately 0.78. |
| • | The diagnostic completes when 30 seconds accumulated time has been spent in the above conditions. |
Conditions for Setting the DTC
The number of rich-to-lean counts is less than 2 or the lean-to-rich counts is less than 2.
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
DTC P1133 is most likely caused by one of the following:
| • | Fuel pressure--The system will go rich if fuel pressure is too high. The PCM can compensate for some increase, however, if pressure gets too high a DTC P0172 will be set. Refer to Fuel System Diagnosis . |
| • | Leaking injector-- A leaking or malfunctioning injector can cause the system to go rich. |
| • | Manifold absolute pressure (MAP) sensor--An output that causes the PCM to sense a higher than normal manifold pressure, or low vacuum, can cause the system to go rich. Disconnecting the MAP sensor will allow the PCM to set a fixed value for the MAP sensor. Substitute a different MAP sensor if the rich condition is gone while the sensor is disconnected. |
| • | Pressure regulator--Inspect for a leaking fuel pressure regulator diaphragm by inspecting for the presence of liquid fuel in the vacuum line to the regulator. |
| • | The throttle position (TP) sensor--An intermittent TP sensor output will cause the system to go rich due to a false indication of the engine accelerating. |
| • | O2S 1 contamination--Inspect O2S 1 for silicone contamination from fuel or use of improper RTV sealant. The sensor may have a white powdery coating and result in a high but false voltage signal, a rich exhaust indication. The PCM will then reduce the amount of fuel delivered to the engine causing a severe surge or driveability problem. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step tests for proper sensor activity. When in Closed Loop fuel control the heated oxygen sensor (HO2S) voltage should rapidly swing above and below the bias voltage.
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This step tests the PCM and the high and low signal circuits between the PCM and the HO2S connector for proper operation.
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This step tests for proper HO2S heater circuit operation up to the HO2S connector.
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This step tests for proper circuit resistance between the HO2S low signal circuit and PCM ground.
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Probable causes include the following: poor O2S low terminal contact at PCM, poor PCM ground connection, high PCM ground circuit resistance and an ungrounded exhaust system.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Does the O2S voltage read fixed within the specified value? | 300-600 mV | Go to Step 4 | Go to Step 3 | |
3 | Were any other DTCs set? | -- | Go to Diagnostic Aids | |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 5 | |
5 |
Does the voltage read less than the specified value? | 20 mV | Go to Step 7 | Go to Step 6 |
6 |
Does the resistance read less than the specified value? | 5 ohms | Go to Step 7 | Go to Step 10 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 8 | |
Does the test lamp illuminate? | -- | Go to Step 12 | Go to Step 9 | |
9 |
Does the resistance measure less than the specified value? | 5 ohms | Go to Step 13 | Go to Step 11 |
10 | Repair the circuit that measured high resistance. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 14 | -- |
Repair the high resistance between the O2S low signal circuit and engine ground. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 14 | -- | |
12 | Replace the O2S sensor. Refer to Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
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 | |
