For 1990-2009 cars

Schematic Reference: Engine Controls Schematics

### Circuit Description

The PCM supplies a bias voltage (approximately 450 mV) on the Heated Oxygen Sensor (HO2S) signal high and low circuits. When the ignition is turned to the ON position, battery voltage is supplied to the HO2S heater. As the heater reaches operating temperature, the HO2S voltage responds by changing from a bias voltage range to normal operation. Typically, as the HO2S reaches operating temperature, the HO2S voltage goes from a bias voltage to a voltage below 300 mV. Depending on the exhaust gas content, it is possible for the HO2S voltage to go above 450 mV.

The PCM will run the heater test only on a cold start (depends on cumulative air flow) and only once an ignition cycle. When the engine is started the PCM will monitor the HO2S voltage. When the HO2S voltage goes above or below the bias range threshold, the PCM will determine how much time it took. If the PCM detects that it took too much time for the HO2S to enter into normal operating range, a DTC will set. The time it takes the HO2S to reach operating temperature is based on the amount of air that flows into the engine.

### Conditions for Setting the DTC

• | DTCs P0100, P0102, P0103, P0112, P0113, P0117, P0118, P0122, P0123, P0131, P0132, P0134, P0200 not set.

• | Engine is started and Intake Air and Engine Coolant temperatures are less than 50°C (122°F) and are within 3°C (5°F) of each other at start-up.

• | Ignition voltage between 10 volts and 16 volts.

• | Engine air flow less than 40 grams per second.

• | TP sensor angle less than 20%.

• | HO2S voltage remains between 300 mV and 700 mV for a predetermined amount of time (depends on engine coolant temperature and air flow).

### Action Taken When the DTC Sets

• | The PCM will illuminate the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.

• | The PCM will record operating conditions at the time the diagnostic fails. The first time the diagnostic fails, this information will be stored in Failure Records. If the diagnostic reports a failure on the second consecutive drive trip, the operating conditions at the time of failure will be written to Freeze Frame and the Failure record will be updated.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.

• | A last test failed (Current DTC) will clear when the ignition is cycled and the diagnostic runs and does not fail.

• | A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | PCM battery voltage is interrupted.

• | Using a Scan tool.

### Diagnostic Aids

• | Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame and/or Failure Records data can be useful in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that were noted. This will isolate when the DTC failed.

• | The heater diagnostic will only run on a cold start and it will only run once per ignition cycle.

• | An oxygen supply inside the HO2S is necessary for proper operation. This supply of oxygen is provided through the HO2S wires. All HO2S wires and connections should be inspected for breaks or contamination. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5).

• | For intermittents, refer to Symptoms .

### Test Description

Number(s) below refer to step numbers on the diagnostic table.

1. The engine must be allowed to cool, as the HO2S maybe at operating temperature and no drop or rise in HO2S voltage would occur. If the HO2S voltage stays between 300-700 mV indicates the HO2S heater is inoperative. For any test that requires probing the PCM or a component harness connector, must use the Connector Test Adapter Kit J 35616-A. Using this kit will prevent damage to the harness connector terminals.

2. If more then one HO2S DTC is set, is good indication that the HO2S fuse is open. Check all related circuits going to all heated oxygen sensors for a short to ground. If all wiring checks to be OK, it may be necessary to disconnect each HO2S one at a time to locate a shorted sensor.

3. Checks whether B+ supply is available at the sensor.

4. Checks whether a ground is available at the sensor.

5. Checks whether the HO2S heater element is internally open.

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 engine has just been operating, allow engine to cool for about one half hour before proceeding.

1. Turn the ignition OFF.
2. Install the scan tool.
3. Turn the ignition ON, engine OFF.
4. Monitor the HO2S voltage display on the Engine 1 Data List of the scan tool.

Does HO2S voltage go from a bias voltage to above or below the specified values?

300-700 mV

Go to Diagnostic Aids

Go to Step 3

3 | Inspect fuse for the HO2S ignition feed. Is HO2S fuse open? | -- | Go to Step 11 | Go to Step 4
4 |

1. Raise the vehicle.
2. Disconnect HO2S electrical connector.
3. Using a test light (J 34142-B) connected to ground (A known good ground. Do not use HO2S heater ground or HO2S low), probe ignition feed circuit at the HO2S electrical connector (PCM side).

Does the test light illuminate?

--

Go to Step 5

Go to Step 7

5 | Connect the test light between HO2S ignition feed and HO2S heater ground. Does the test light illuminate? | -- | Go to Step 6 | Go to Step 8
6 | Using a DVM (J 39200), measure resistance between HO2S ignition feed and HO2S heater ground at HO2S pigtail. Is the HO2S resistance within the specified values? | 3.5-14.0 ohms | Go to Step 9 | Go to Step 10
7 | Repair the open in the HO2S ignition feed circuit to HO2S. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Is the action complete? | -- | Go to Step 12 | --
8 | Repair the open in the HO2S heater ground circuit. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Is the action complete? | -- | Go to Step 12 | --
9 |

1. Check for a poor connection at the HO2S harness terminals.
2. If a poor connection is found, replace terminals. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5).

Was a poor connection found?

--

Go to Step 12

Go to Step 10

10 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | Go to Step 12 | --
11 | Locate and repair the short to ground in HO2S ignition feed circuit and replace the faulty fuse. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Is the action complete? | -- | Go to Step 12 | --
12 |

1. Using the scan tool, select DTC, Clear Info.
2. Start the engine and idle at normal operating temperature.
3. Select DTC, Specific, then enter the DTC number which was set.
4. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text, if applicable.

Does the scan tool indicate that this test ran and passed?

--

Go to Step 13

Go to Step 2

13 | Using the scan tool, select Capture Info, Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK