Circuit Description
The powertrain control module (PCM) continuously monitors the heated oxygen sensor (HO2S) 1 activity for 100 seconds. During the monitoring period, the PCM counts the number of times that the HO2S 1 switches from rich-to-lean, and from lean-to-rich, then adds the time that the HO2S 1 took to complete all the switches. With this information, an average time for all switches can be determined. Whenever the average time to switch is too slow, a DTC P0133 will set.
Conditions For Running The DTC
| • | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0201-P0204, P0300, P0301-P0304, P0335, P0440, P0442, P0446, P0506, P0507, P0601, P0602, or P1441 are not set. |
| • | The engine coolant temperature (ECT) is more than 70°C (158°F). |
| • | The battery voltage is greater than 10 volts. |
| • | The fuel level is greater than 10 percent. |
| • | The engine run time is greater than 10 seconds. |
| • | The engine speed is between 1,600-2,450 RPM. |
| • | The engine is operating in Closed Loop. |
| • | The throttle position (TP) angle is between 9-18 percent. |
| • | The evaporative emissions (EVAP) control system is commanded open for more than 36 percent. |
| • | The purge learned memory is more than approximately 0.78. |
| • | The diagnostic completes when 30 seconds of accumulated time has been spent in the above conditions. |
Conditions For Setting The DTC
The average HO2S 1 response times are more than 1,119 mS for rich-to-lean sweeps, or 760 mS for lean-to-rich sweeps.
Or
Sum of rich-to-lean and lean-to-rich is greater than 1,235 mS.
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
DTC P0133 or slow response is most likely caused by one of the following conditions:
| • | The fuel pressure--The system will go rich if the fuel pressure is too high. The PCM can compensate for some increase, but if the fuel pressure becomes too high, DTC P0172 may set. Refer to the Fuel System Diagnosis . |
| • | A leaking injector--A leaking or malfunctioning injector can cause the system to go rich. |
| • | The manifold absolute pressure (MAP) sensor--An output that causes the PCM to sense a higher than normal manifold pressure, or a low vacuum, can cause the system to go rich. Disconnecting the MAP sensor will allow the PCM to set a fixed value for the MAP sensor. Substitute a different MAP sensor if the rich condition is gone while the MAP sensor is disconnected. |
| • | The pressure regulator--Inspect for a leaking fuel pressure regulator diaphragm by confirming the presence of liquid fuel in the vacuum line to the fuel pressure regulator. |
| • | The TP sensor--An intermittent TP sensor output can cause the system to go rich due to a false indication of the engine accelerating. |
| • | HO2S 1 contamination--Inspect the HO2S 1 for silicone contamination from fuel or from the use of an improper room-temperature vulcanizing (RTV) sealant. The HO2S 1 may have a white powdery coating which will result in a high but false voltage signal, indicating a rich exhaust. The PCM will then reduce the amount of fuel delivered to the engine, causing a severe surge or driveability problem. |
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 evidence of the removal or tampering of the fuel filter 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 an 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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If the voltage observed in Step 9 is less than the range specified, a short between the high and low signal circuits or a short between the high signal circuit and ground is indicated. With the HO2S and the PCM disconnected the resistance between the high and low signal circuits and the resistance between the high signal 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 less than the voltage specified, a high resistance, or an open, high, or low signal 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 1 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 | |||||||||||
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Important: If any other DTCs are set, except HO2S DTCs, refer to the other DTCs before proceeding with this table.
Does the scan tool indicate HO2S voltage varying outside the specified values? | 400-500 mV | Go to Step 3 | Go to Step 4 | |||||||||||
3 | Are any powertrain component DTCs set? | -- | Go to Step 5 | |||||||||||
Did you complete the replacement? | -- | Go to Step 14 | -- | |||||||||||
5 |
Did this DTC Run and Fail This Ignition? | -- | Go to Step 7 | Go to Step 6 | ||||||||||
6 | This DTC is intermittent. Are any additional DTCs stored? | -- | Go to Diagnostic Aids | |||||||||||
Repair the exhaust system as necessary. Refer to Exhaust Leakage in Engine Exhaust. Repair the connectors as necessary. Refer to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 8 | |||||||||||
8 |
Does the voltage measure within the specified value? | 351-551 mV | Go to Step 9 | Go to Step 11 | ||||||||||
9 |
Does the HO2S 1 voltage measure less than the value specified? | 20 mV | Go to Step 10 | Go to Step 12 | ||||||||||
10 |
HO2S 1 contamination sources include the following:
Did you complete the action? | -- | Go to Step 13 | -- | ||||||||||
Repair the short between the HO2S 1 high and low signal circuits or between the HO2S 1 high signal circuit and a voltage source. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 15 | -- | |||||||||||
Did you complete the repair? | -- | Go to Step 15 | -- | |||||||||||
13 | Inspect for poor connections at the harness connector of the HO2S 1. Refer to Testing for Intermittent Conditions and Poor Connections and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14 | ||||||||||
14 | Replace the HO2S 1. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||||||
15 |
Does the DTC run and pass? | -- | Go to Step 16 | Go to Step 2 | ||||||||||
16 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||
