For 1990-2009 cars
Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The powertrain control module (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

1. No TP sensor, EVAP system, misfire, IAT sensor, MAP sensor, Fuel trim, injector circuit, EGR Pintle Position, MAF sensor, ECT sensor, CKP sensor, or H02S sensor 1 heater circuit DTCs set.
2. Mass Air Flow is between 10 g/s and 30 g/s.
3. ECT is greater than 50°C (122°F).
4. Engine run time is greater than 60 seconds.
5. Engine speed is between 1000 RPM and 3000 RPM.
6. The engine is running in closed loop.

### Conditions for Setting the DTC

• | The above conditions are present for a 100 second monitoring period.

• | The PCM monitors fewer than 40 rich to lean and 40 lean to rich switches for HO2S 1.

### Action Taken When the DTC Sets

• | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

• | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

### 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

A poor connection in the HO2S heater ignition feed or ground circuit may cause the DTC to set. Check HO2S heater circuitry for intermittent malfunctions or poor connections. If connections and wiring are OK and the DTC continues to set, replace the HO2S 1.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

### Test Description

The numbers below refer the step numbers on the diagnostic table.

1. This step checks for conditions which may cause the DTC to set with a good heated oxygen sensor. Correct any of the described conditions if present.

2. Before replacing the HO2S, check 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.

   .

#### DTC P1133 - HO2S Insufficient Switching Sensor 1

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Important: If any DTCs are set (except P1134), go to those DTCs before proceeding with this diagnostic table.

1. Operate the vehicle within parameters specified under Conditions for Setting the DTC criteria included in Diagnostic Support.
2. Monitor Specific DTC info for DTC P1133 until the DTC P1133 test runs using a scan tool.

Does the scan tool indicate DTC failed this ignition?

--

Go to Step 3

Go to Diagnostic Aids

3 |

1. Check the exhaust system for leaks. Refer to Exhaust Leakage - Not OBD II .
2. If an exhaust leak is found, repair as necessary.

Was a problem found?

--

Go to Step 11

Go to Step 4

4 | Visually and physically inspect the following items:

• | Ensure that the HO2S 1 is securely installed.

• | Check for corrosion on terminals.

• | Check terminal tension at HO2S 1 and at the PCM.

• | Check for damaged wiring.

Was a problem found in any of the above areas?

--

Go to Step 8

Go to Step 5

5 |

1. Disconnect the HO2S 1 and jumper HO2S low (PCM side) signal circuit to ground.
2. Monitor HO2S 1 voltage using a scan tool.

Does the scan tool indicate voltage near the specified value?

450 mV

Go to Step 6

Go to Step 9

6 |

1. Jumper the HO2S 1 high and low (PCM side) signal circuits to ground.
2. Monitor HO2S 1 voltage using a scan tool.

Does the scan tool indicate a voltage less than the specified value?

300 mV

Go to Step 7

Go to Step 10

7 | Replace the affected Heated Oxygen Sensor(s). Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | Go to Step 11 | --
8 | Repair the condition as necessary. Is the action complete? | -- | Go to Step 11 | --
9 | Repair the open HO2S 1 low signal circuit or grounded HO2S 1 high signal circuit. Refer to Heated Oxygen Sensor Wiring Repairs . Is the action complete? | -- | Go to Step 11 | --
10 | Repair the open HO2S 1 high signal circuit or poor connections at the PCM. Refer to Heated Oxygen Sensor Wiring Repairs . Is the action complete? | -- | Go to Step 11 | --
11 |

1. Clear the DTCs.
2. Operate the vehicle within parameters specified under Conditions for Setting the DTC criteria included in Diagnostic Support.
3. Monitor Specific DTC info for DTC P1133 until the DTC P1133 test runs using a scan tool.

Does the scan tool indicate the DTC failed this ignition?

--

Go to Step 2

System OK