P1133

Circuit Description
The Engine Control Module (ECM) constantly monitors the Oxygen Sensor (O2S) activity for 100 seconds. During the monitor period, the ECM counts the number of times that the O2S switches from rich to lean and from lean to rich. With this information, a total for all switches can be determined. If the number of switches is too low, Diagnostic Trouble Code (DTC) P1133 will set. The lean- to-rich and the rich-to-lean are less than 20 switches.

Conditions for Setting the DTC
- DTCs P0106, P0107, P0108, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0134, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0336, P0337, P0351, P0352, P0402, P0404, P0405, P0406, P0506, P0507, P1404, P1441 and P1627 are not set.
- Closed Loop stoichiometry.
- Purge duty cycle is greater than 0%.
- Engine Coolant Temperature (ECT) is greater than 162 °F (72 °C).
- Engine run time is at least two minutes.
- Calculated airflow is between 9 and 40 grams/sec.
- Engine speed is between 1600 rpm and 4000 rpm.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- Open loop fuel control will be in effect.
- The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the freeze frame and failure records buffers.
- A history DTC is stored.

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 have occurred without a fault.
- DTC(s) can be cleared by using the scan tool.

Diagnostic Aids
DTC P1133 is most likely caused by one of the following items:
- Fuel Pressure - The system will go rich if the fuel pressure is too high. The ECM can compensate for some increase. However, if it gets too high, a DTC P1133 may 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 ECM to sense a higher than normal manifold pressure (low vacuum) can cause the system to go rich. Disconnecting the MAP sensor will allow the ECM 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 - Check for a leaking fuel pressure regulator diaphragm by checking for the presence of liquid fuel in the vacuum line to the pressure regulator.

- Throttle Position (TP) sensor - An intermittent TP sensor output can cause the system to go rich due to a false indication of the engine accelerating.

- O2S contamination - Inspect the O2S for silicone contamination from fuel or improper use of Room Temperature Vulcanizing (RTV) sealant. The sensor may have a white powdery coating and result in a high but false voltage signal (rich exhaust indication). The ECM will then reduce the amount of fuel delivered to the engine causing a severe surge or driveability problem.

Steps 1 - 6:

Steps 7 - 14:

Steps 15 - 16:

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
14. The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming
16. If no malfunctions have been found at this point and no additional DTCs are set, refer to "Diagnostic Aids" for additional checks and information.