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 a 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 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 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 determines if the difference in transition times from lean-to-rich or rich-to-lean has exceeded a maximum ratio. The powertrain control module (PCM) monitors the time needed for the HO2S to transition from more than 600 mV to less than 300 mV and vice versa. If either of these times is longer than the other by a calibrated ratio, this DTC is set.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0134, P0135, P0151, P0152, P0154, P0155, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404, or P1441 are not set. |
| • | The engine coolant temperature (ECT) is more than 57°C (135°F). |
| • | The engine run time is more than 160 seconds. |
| • | The mass air flow (MAF) sensor is between 15-55 g/s. |
| • | The engine speed is between 1,100-3,000 RPM. |
| • | The throttle position (TP) is more than 5 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. |
| • | The above conditions are met for 100 seconds. |
Conditions for Setting the DTC
The HO2S transition time ratio is not within a calibrated range.
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 correct wire and connector repairs, refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Inspect for the following conditions:
| • | An improperly installed air cleaner outlet duct |
| • | A collapsed or restricted air cleaner outlet duct , or a missing or plugged air filter |
| • | Any throttle body or intake manifold vacuum leaks |
| • | A damaged or blocked throttle body inlet |
| • | Any corrosion, leaks, or loose or missing hardware in the exhaust system |
| Refer to Exhaust Leakage in Engine Exhaust. |
| • | Verify that the HO2S is installed securely and the pigtail harness is not contacting the exhaust manifold or any wires. |
| • | A contaminated HO2S |
| • | Any splits, kinks, or incorrect connections in the vacuum hoses |
| • | Any excessive water, alcohol, or other contaminants in the fuel |
| Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| • | Verify that the PCM sensor grounds that are clean, tight, and properly positioned. |
Inspect for an intermittent condition. 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 , or refer to Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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HO2S contamination is indicated if multiple response, switching, or time ratio HO2S DTCs are set.
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Even small exhaust leaks can cause a slow response from the HO2S.
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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 un-approved 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.
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If the voltage observed in Step 8 is less than the range specified, a short between the high and low circuits or a short between the high circuit and ground is indicated. With the HO2S and the PCM disconnected the resistance between the high and low circuits and the resistance between the high circuit and ground should measure infinite.
If the voltage observed in Step 8 is more than the range specified a short between the high circuit and an ignition voltage source is indicated.
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If the voltage observed in Step 9 is not below the voltage specified a high resistance high or low circuit is indicated.
Good circuit continuity measures less than 5 ohms with the PCM and sensor disconnected. Measure between the PCM connector and the HO2S connector. Ensure that the PCM terminal contact is good.
Step | Action | Values | Yes | No | ||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||||||||||||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||||||||||||||||||||
In addition to this DTC, check for the following HO2S DTCs:
Are any of the above listed HO2S DTCs set? | -- | Go to Step 4 | Go to Step 3 | |||||||||||||||||||||||||||||||
3 | Are any powertrain component DTCs set? | -- | Go to Step 5 | |||||||||||||||||||||||||||||||
4 |
Has the contamination source been removed and the affected sensors replaced? | -- | Go to Step 18 | -- | ||||||||||||||||||||||||||||||
5 |
Did the DTC run and fail this ignition? | -- | Go to Step 7 | Go to Step 6 | ||||||||||||||||||||||||||||||
6 |
Did you find and correct the condition? | -- | Go to Step 18 | Go to Diagnostic Aids | ||||||||||||||||||||||||||||||
Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 8 | |||||||||||||||||||||||||||||||
8 |
Is the HO2S voltage within the specified range? | 351-51 mV | Go to Step 9 | Go to Step 13 | ||||||||||||||||||||||||||||||
9 |
Is the HO2S voltage less than the specified value? | 20 mV | Go to Step 10 | Go to Step 14 | ||||||||||||||||||||||||||||||
10 |
Does the test lamp illuminate? | -- | Go to Step 11 | Go to Step 15 | ||||||||||||||||||||||||||||||
11 | Connect the test lamp between the HO2S heater ignition 1 voltage circuit terminal and the HO2S heater ground circuit terminal. Both terminals are on the engine harness side. Does the test lamp illuminate? | -- | Go to Step 12 | Go to Step 16 | ||||||||||||||||||||||||||||||
HO2S contamination sources include the following:
Did you complete the action? | -- | Go to Step 17 | -- | |||||||||||||||||||||||||||||||
Did you complete the action? | -- | Go to Step 18 | Go to Diagnostic Aids | |||||||||||||||||||||||||||||||
Did you complete the action? | -- | Go to Step 18 | -- | |||||||||||||||||||||||||||||||
15 | Repair the ignition 1 voltage circuit to the HO2S heater . Refer to Wiring Repairs in Wiring Systems. Did you complete the action? | -- | Go to Step 18 | -- | ||||||||||||||||||||||||||||||
16 | Repair the HO2S heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the action? | -- | Go to Step 18 | -- | ||||||||||||||||||||||||||||||
17 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 , or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 . Did you complete the action? | -- | Go to Step 18 | -- | ||||||||||||||||||||||||||||||
18 |
Does the DTC run and pass? | -- | Go to Step 19 | Go to Step 2 | ||||||||||||||||||||||||||||||
19 |
Did the diagnostic run and pass this ignition? | -- | System OK | |||||||||||||||||||||||||||||||
