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 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.
Certain vehicle models utilize an oxygen sensor behind the catalytic converter in order to monitor catalyst efficiency.
This diagnostic trouble code (DTC) determines if the HO2S is functioning properly. The DTC checks for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV. This DTC sets when the powertrain control module (PCM) fails to detect a minimum number of voltage transitions above and below the bias range during the test period.
This DTC is designed to detect an HO2S that produces too few lean to rich and rich to lean signal transitions within a calibrated time window.
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 system voltage is above 9 volts. |
| • | The system is in a Closed Loop. |
| • | The engine control temperature (ECT) is more than 57°C (135°F). |
| • | The engine has been running for more than 160 seconds. |
| • | The mass air flow (MAF) is between 15-55 g/s. |
| • | The engine speed is between 1,100-3,000 RPM. |
| • | The EVAP canister purge is active. |
| • | The accelerator pedal position (APP) indicated angle is above 5 percent. |
Conditions for Setting the DTC
The number of lean-to-rich and rich-to-lean transitions within a 100-second sample period were less than a calibrated number.
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 proper wire and connector repairs, refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems.
Check for the following conditions:
| • | An improperly installed air cleaner outlet duct |
| • | The air cleaner outlet duct for a collapsed duct, for restrictions, or for a missing or plugged air filter. |
| • | Throttle body and intake manifold vacuum leaks |
| • | A damaged or blocked throttle body inlet |
| • | Exhaust system for corrosion, leaks, or loose or missing hardware--Refer to Exhaust Leakage in Engine Exhaust. |
| • | The HO2S is installed securely and the pigtail harness is not contacting the exhaust manifold or wires |
| • | HO2S contamination |
| • | The vacuum hoses for splits, kinks, and proper connections |
| • | Excessive water, alcohol, or other contaminants in the fuel--Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| • | PCM sensor grounds that are clean, tight, and properly positioned |
If the problem is intermittent, refer to Intermittent Conditions .
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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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 unapproved silicon room temperature vulcanizing (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 become 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 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 get contaminated.
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If the voltage observed in step 8 is less than the specified range, a short between the HO2S high signal and the low reference circuits, or a short between the HO2S high signal circuit and ground is indicated. With the HO2S and the PCM disconnected, the resistance between the HO2S high signal and low reference circuits and the resistance between the HO2S high signal circuit and ground should measure infinite.
If the voltage observed in step 8 is more than the specified range, a short between the HO2S 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, or an open in the HO2S high signal and low reference 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 | ||||||||||||||||||||||||||||||||
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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 other DTCs set? | -- | Go to Step 5 | |||||||||||||||||||||||||||||||||
Important: The contamination source must be removed prior to operating the engine with the replacement sensors.
Has the contamination source been removed and have the affected sensors been replaced? | -- | Go to Step 19 | -- | |||||||||||||||||||||||||||||||||
5 |
Did this DTC run and fail this ignition? | -- | Go to Step 7 | Go to Step 6 | ||||||||||||||||||||||||||||||||
6 | The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:
Repair any of the above or similar engine conditions as necessary. Did you find and correct the condition? | -- | Go to Step 19 | Go to Diagnostic Aids | ||||||||||||||||||||||||||||||||
Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 8 | |||||||||||||||||||||||||||||||||
8 |
Is the HO2S voltage within the value range specified? | 351-551 mV | Go to Step 9 | Go to Step 13 | ||||||||||||||||||||||||||||||||
9 |
Is the HO2S voltage less than the value specified? | 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 | -- | |||||||||||||||||||||||||||||||||
Did you find and correct the condition? | -- | Go to Step 19 | Go to Diagnostic Aids | |||||||||||||||||||||||||||||||||
Did you complete the repair? | -- | Go to Step 19 | -- | |||||||||||||||||||||||||||||||||
15 | Repair the HO2S heater 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 Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 18 | ||||||||||||||||||||||||||||||||
18 | Replace the appropriate HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or 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 | |||||||||||||||||||||||||||||||||
