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 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 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. Certain vehicles use an oxygen sensor behind the catalytic converter in order to monitor the catalyst efficiency.
This DTC is designed to detect an HO2S that is slow to respond to changes in the exhaust oxygen content.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0128, P0200, P0300, P0351-P0358, P0401, P0404, P0405, P0410, P0418, P0443, P0446, P0449, P1120, P1220, P1221, P1258, or P1404 are not set. |
| • | The secondary air injection (AIR) and the exhaust gas recirculation (EGR) diagnostics are not active. |
| • | The ECT is more than 57°C (135°F). |
| • | The ignition voltage is more than 9 volts. |
| • | The fuel system is operating in Closed Loop. |
| • | The engine speed is between 1,000-3,000 RPM. |
| • | The engine air flow is between 1,555 g/s. |
| • | The EVAP canister purge duty cycle is more than 0 percent. |
| • | The engine run time is more than 160 seconds. |
| • | The fuel level is more than 10 percent. |
Conditions for Setting the DTC
| • | The lean to rich response average time is more than 250 milliseconds. |
| • | The rich to lean response average time is more than 160 milliseconds. |
| • | The above conditions are met for 100 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
| • | This diagnostic only runs once per ignition cycle. |
| • | A malfunction in the HO2S heater circuits causes a DTC to set. Check HO2S heater circuits for intermittent opens and connections. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. |
| • | Use the Freeze Frame and Failure Records data in order to locate an intermittent condition in the following ways: |
| - | If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in determining how many miles since the DTC set. |
| - | The Fail Counter and Pass Counter can also aid in determining how many ignition cycles the diagnostic reported a pass or a fail. |
| - | Operate the vehicle within the same Freeze Frame conditions that you observed in order to isolate when the DTC failed. Use the following conditions for your tests: |
| • | RPM |
| • | Load |
| • | Vehicle speed |
| • | Temperature |
| - | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The number below refers to the step number 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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The use of leaded fuel may be indicated by the removal or tampering of the fuel filler restrictor.
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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Even small exhaust leaks can cause 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 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 the 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 the 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 signal circuit and an ignition voltage source is indicated.
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If the voltage observed in step 9 is not below the specified voltage, 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 inspect for the following HO2S DTCs:
Are any of the above HO2S DTCs set? | -- | Go to Step 4 | Go to Step 3 | |||||||||||||||||||||||||||||||
3 | Are any powertrain component DTCs set? | -- | Go to Step 5 | |||||||||||||||||||||||||||||||
Important: The contamination source must be removed prior to operating the engine with the replacement sensors.
Did you complete the replacement? | -- | Go to Step 19 | -- | |||||||||||||||||||||||||||||||
5 |
Did this 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 19 | Go to Diagnostic Aids | ||||||||||||||||||||||||||||||
Repair the exhaust as necessary. Repair the terminal contact as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 8 | |||||||||||||||||||||||||||||||
8 |
Does the HO2S voltage measure within the specified range? | 351-551 mV | Go to Step 9 | Go to Step 13 | ||||||||||||||||||||||||||||||
9 |
Does the HO2S voltage measure 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 |
Does the test lamp illuminate? | -- | Go to Step 12 | Go to Step 16 | ||||||||||||||||||||||||||||||
Did you complete the repair? | -- | Go to Step 17 | -- | |||||||||||||||||||||||||||||||
Repair the short between the HO2S high signal and low reference circuits or between the HO2S high signal circuit and a voltage source. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 19 | -- | |||||||||||||||||||||||||||||||
Did you find and correct the condition? | -- | Go to Step 19 | -- | |||||||||||||||||||||||||||||||
15 | Repair the HO2S high control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 19 | -- | ||||||||||||||||||||||||||||||
16 | Repair the HO2S heater low control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 19 | -- | ||||||||||||||||||||||||||||||
17 | Inspect for poor connections at the harness connector of the affected HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 18 | ||||||||||||||||||||||||||||||
18 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or to Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 . Did you complete the replacement? | -- | Go to Step 19 | -- | ||||||||||||||||||||||||||||||
19 |
Does the DTC run and pass? | -- | Go to Step 20 | Go to Step 2 | ||||||||||||||||||||||||||||||
20 | Use a scan tool in order to observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||||||||||||||||||||
