Circuit Description
The 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 DTC P1133 will set.
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 engine run time is more than 10 seconds. |
| • | ECT is more than 75°C (167°F). |
| • | Engine speed is between 1600 RPM and 2600 RPM. |
| • | Engine is operating in closed loop. |
| • | Throttle Position (TP) angle is between 14 percent and 26 percent. |
| • | Evaporative emissions control system is commanded open for more than 40 percent. |
| • | Purge learned memory is more than 191. |
Conditions for Setting the DTC
The number of rich to lean counts is less than 1 or the lean to rich counts is less than 1.
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
DTC P1133 is most likely caused by one of the following:
| • | Fuel pressure - The system will go rich if fuel pressure is to high. The PCM can compensate for some increase, however, if it 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. |
| • | MAP sensor - An output that causes the PCM to sense a higher than normal manifold pressure (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 - Check for a leaking fuel pressure regulator diaphragm by checking for the presence of liquid fuel in the vacuum line to the regulator. |
| • | 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 (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 checks for proper sensor activity. When in Closed Loop fuel control the HO2S voltage should rapidly swing above and below the bias voltage.
-
This step checks the VCM and the HIGH and LOW circuits between the VCM and the HO2S connector for proper operation.
-
This step checks for proper HO2S heater circuit operation up to the HO2S connector.
-
This step checks for proper circuit resistance between the HO2S LOW circuit and VCM ground.
-
This step checks for proper circuit resistance between the HO2S LOW circuit and VCM ground with a COLD sensor. A loose HO2S or poor tread to exhaust electrical contact will cause higher resistance when the HO2S is cold. Although 500 ohms is allowed, typical resistance should be less than 50 ohms.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||
Is the O2S voltage fixed within the voltage range specified? | 300-600 mV | |||||||||||
3 | This DTC is intermittent. Are any additional DTCs stored? | -- | Go to the applicable DTC table | Go to Diagnostic Aids | ||||||||
The leak may be very small and typically be within 12 inches of the suspect O2S. Did you find and repair a problem? | -- | |||||||||||
5 |
Is the voltage less than the specified value? | 20 mV | ||||||||||
6 |
Is the resistance of the circuit less than the specified value? | 5 ohms | ||||||||||
Did you find and repair a problem? | -- | |||||||||||
Connect a test lamp between the O2S LOW circuit (PCM side) and Battery positive terminal. Is the test lamp ON? | -- | |||||||||||
9 |
Is the resistance less than the specified value? | 5 ohms | ||||||||||
10 | Repair the circuit that measured high resistance. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
11 | Repair the high resistance between the O2S LOW circuit and engine ground. Refer to Wiring Repairs in Wiring Systems. Probable causes include the following:
Is the action complete? | -- | -- | |||||||||
12 | Replace the O2S sensor. Refer to Oxygen Sensor Replacement Is the action complete? | -- | -- | |||||||||
|
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||||||||||
14 |
Does the scan tool indicate the diagnostic passed? | -- | ||||||||||
15 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable table | System OK |
