For 1990-2009 cars
Engine Controls Components
HO2S 1 and HO2S 2
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 more 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

• | There are no active MAF, TP, IAT, MAP, ECT, AIR Sensor, Injector Circuit, EVAP, or HO2S Heater DTCs.

• | The mass air flow is between 10-30 g/s.

• | The ECT is more than 50°C (122°F).

• | The engine speed is between 1000-3000 RPM.

• | The vehicle is not in Park or Neutral.

• | The ignition voltage is between 9.0-18.0 volts.

• | The air pump is commanded OFF.

• | The above conditions are present for a 100-second monitoring period after Closed Loop.

### Conditions for Setting the DTC

• | The PCM monitors fewer than 65 rich to lean and 50 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 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 malfunction in the HO2S heater ignition feed or ground circuit may cause a DTC P1133 to set. Inspect the HO2S heater circuitry for intermittent faults or faulty connections, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. If connections and wiring are OK and DTC P1133 continues to set, replace the HO2S 1. Refer to Heated Oxygen Sensor Replacement .

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.

• | Faulty terminal connections--Inspect the harness connectors for the following conditions:

- | Backed-out terminals

- | Improper mating

- | Broken locks

- | Improperly formed or damaged terminals

- | Faulty terminal-to-wire connection--Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

• | A damaged harness--Inspect the wiring harness for damage.

| If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

• | Clean and secure the connections at the PCM and the engine grounds.

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.

### Test Description

The numbers below refer to the step numbers on the diagnostic table:

1. When the system is operating correctly the HO2S voltage should toggle above and below the specified values.

2. If the low circuit is shorted to ground the HO2S voltage will be less than 400 mV when the signal circuit is jumped to ground.

3. The specified value is what is measured on a correctly operating system.

4. The specified value is what is measured on a correctly operating system.

5. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Important: If any other DTCs are set, except HO2S DTCs, refer to the other DTCs first before proceeding .

1. Ensure that the engine is at operating temperature.
2. Operate the engine above 1200 RPM for two minutes.
3. With a scan tool, observe the HO2S voltage parameter.

Does scan tool indicate HO2S voltage varying outside the specified values?

400-500 mV

Go to Step 3

Go to Step 4

3 | Operate the vehicle within Failure Records conditions. Does the scan tool indicate this DTC failed this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids
4 | Inspect and test for the following:

• | Exhaust leak. Refer to Exhaust System Inspection and Exhaust Leakage - Not OBD II in Engine Exhaust.

• | The HO2S is installed correctly.

• | Damaged wiring. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 5

5 |

1. Turn ON the ignition.
2. Disconnect the HO2S.
3. Jumper the signal circuit on the PCM side to a good ground.
4. With a scan tool, observe the HO2S voltage parameter.

Does the scan tool indicate that the HO2S voltage is more than the specified value?

400 mV

Go to Step 6

Go to Step 10

6 |

1. Remove the jumper wire.
2. Measure the voltage on the HO2S signal circuit on the PCM side, using a DMM that is connected to a good ground.

Does the voltage measure near the specified value?

4.5V

Go to Step 7

Go to Step 9

7 | Measure the voltage on the HO2S low circuit on the PCM side, using a DMM that is connected to a good ground. Does the voltage measure near the specified value? | 5.0V | Go to Step 11 | Go to Step 8
8 | Test the low circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 13
9 | Test the signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 13
10 | Test the low circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14
11 | Test for faulty connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12
12 | Important: Determine the cause of contamination before replacing the sensor. Inspect and test for the following:

• | Fuel Contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Engine oil or coolant consumption. Refer to Oil Consumption Diagnosis in Engine Mechanical.

• | Use of an improper room-temperature vulcanizing (RTV) sealant. 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. in Cautions and Notices.

Replace the HO2S1 sensor. Refer to Heated Oxygen Sensor Replacement .

Did you complete the replacement?

--

Go to Step 15

--

13 | Test for faulty connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14
14 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | Go to Step 15 | --
15 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Failure Record conditions.

Does the DTC reset?

--

Go to Step 2

Go to Step 16

16 | Use the scan tool in order to check for DTCs. Does the scan tool indicate any DTCs that you have not diagnosed? | -- | Go to applicable DTC table | System OK