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For 1990-2009 cars only

Circuit Description

The heated oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm the sensor to the operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches the operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or "lean out" the mixture, when the HO2S detects a rich exhaust condition.

This DTC is designed to detect an HO2S voltage that remains high for more than a specified number of seconds during the test conditions.

Conditions for Running the DTC

    • DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1414, or P1441 are not set.
    • The air fuel ratio is between 14.5:1 and 14.7:1.
    • The throttle position (TP) is between 3-70 percent.
    • The loop status is closed.
    • The ignition 1 signal is between 9-18 volts.
    • The fuel tank level remaining is more than 10 percent.
    • Intrusive tests are not in progress.
    • Scan tool output controls are not active.

Conditions for Setting the DTC

The HO2S voltage is more than 994 mV for 550 seconds.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

Important: Never solder the HO2S wires. For the proper wire and connector repair procedures, refer to Wiring Repairs in Wiring Systems.

Check the following items:

    • The fuel pressure--If the pressure is too high the system will run rich. The powertrain control module (PCM) can compensate for some increase. However, if the pressure gets too high, the DTC may set. Refer to Fuel System Diagnosis .
    • A rich injector--Perform a Fuel Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 .
    • A leaking injector--Refer to Fuel System Diagnosis .
    • The engine oil contaminated by fuel
    • The evaporative emission (EVAP) canister purge--Check for a fuel saturation. If the canister is full of fuel, check the canister control and the hoses. Refer to Evaporative Emission Canister Purge Solenoid Valve Replacement .
    • A leaking fuel pressure regulator diaphragm--Check the vacuum line to the regulator for fuel.
    • The TP sensor--An intermittent TP sensor output causes the system to run rich due to a false indication of the throttle moving.
    • A false rich indication due to silicon contamination of the heated oxygen sensor--A DTC P0144 accompanied by lean driveability conditions and a powdery white deposit on the sensor indicates a false rich indication.

An intermittent can be caused by any of the following conditions:

    • A poor connection
    • Rubbed-through wire insulation
    • A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. If a repair is necessary, refer to Wiring Repairs , or Connector Repairs in Wiring Systems.

Test Description

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

  1. Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor check for rich conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S is defective or a rich condition exists only on the suspect HO2S cylinder bank.

  2. An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of unapproved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also be contaminated.

Step

Action

Value(s)

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

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Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Run the engine until the engine reaches a normal operating temperature.
  2. Using a scan tool, monitor the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage fixed at more than the specified value?

944 mV

Go to Step 4

Go to Step 3

3

  1. The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:
  2. •  A signal wire intermittently shorted to voltage
    • Any water intrusion into the HO2S connector
    • A silicon contaminated HO2S
    • An intermittent rich engine condition such as the following:
       - An EVAP canister purge condition
       - The engine oil contaminated by fuel
       - An incorrect fuel pressure
       - A leaking fuel pressure regulator
       - Any rich fuel injectors
       - An inaccurate mass air flow (MAF) sensor
       - A rich engine condition during DFCO operation
  3. Repair any of the above or similar engine conditions as necessary.

Did you find a problem?

--

Go to Step 10

Go to Diagnostic Aids

4

  1. Turn the ignition OFF.
  2. Disconnect the HO2S connector for the sensor that applies to this DTC.
  3. Turn the ignition ON, leaving the engine OFF.
  4. Using the scan tool, monitor the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage within the specified range?

351-551 mV

Go to Step 5

Go to Step 6

5

  1. The HO2S is detecting a rich exhaust condition or may be contaminated. Check for one of the following conditions:
  2. • Any water intrusion into the HO2S connector
    • A silicon contaminated HO2S
    • The engine oil contaminated by fuel
    • An EVAP canister purge condition
    • An incorrect fuel pressure
    • A leaking fuel pressure regulator
    • Any rich fuel injectors
    • An inaccurate mass air flow (MAF) sensor
  3. Repair any of the above or similar engine conditions as necessary.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 8

6

  1. Turn the ignition OFF.
  2. Disconnect the PCM connector that contains the HO2S high signal circuit.
  3. Turn the ignition ON, leaving the engine OFF.
  4. Using a DMM, measure the voltage between the HO2S high signal circuit and ground on the harness side of the PCM connector terminal.

Is the voltage more than the specified value?

20 mV

Go to Step 7

Go to Step 9

7

Repair the short to voltage in the HO2S high signal circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the action?

--

Go to Step 10

--

8

Important: Before replacing a contaminated HO2S, determine and repair the cause of the contamination.

Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 .

Did you complete the action?

--

Go to Step 10

--

9

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the action?

--

Go to Step 10

--

10

  1. Using the scan tool, clear the DTC information.
  2. Operate the vehicle within the Conditions for Running the DTC.
  3. Observe the DTC Status for this DTC.

Did this DTC run and pass?

--

Go to Step 11

Go to Step 2

11

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK