Circuit Description
The DTC P0136 Heated Oxygen Sensor (HO2S) Circuit Sensor 2 diagnostic monitors the operation of the post catalyst oxygen sensor. In order to control emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), a three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting the HC and the CO into harmless water vapor and carbon dioxide. The catalyst also reduces NOx by converting the NOx to nitrogen. The powertrain control module (PCM) has the ability to monitor this process using the heated oxygen sensors HO2S 1 and HO2S 2. The HO2S 1 produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the three-way catalytic converter. The HO2S 2 produces an output signal which indicates the oxygen storage capacity of the catalyst. This in turn indicates the catalysts ability to convert exhaust gases efficiently. If the catalyst is operating efficiently, the HO2S 1 signal will be far more active than that produced by the HO2S 2.
Conditions for Running the DTC
| • | The engine coolant temperature (ECT) is more than or equal to 70°C (158°F). |
| • | The engine speed is more than 1,600 RPM. |
Conditions for Setting the DTC
| • | The average HO2S 2 voltage is more than or equal to 400 mV. |
| • | The average HO2S 2 voltage is less than or equal to 500 mV. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) during the second key cycle in which the DTC sets. |
| • | The PCM stores the conditions which were present when the DTC set as Freeze Frame data. |
| • | The PCM will turn the HO2S 2 heater OFF. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present. |
| • | A DTC clears after 40 consecutive warm-up cycles have occurred without a fault. |
| • | A DTC can be cleared by using the scan tool Clear DTC Information function. |
Diagnostic Aids
Check for the following conditions:
| • | Inspect the wiring harness for damage. If the harness appears to be OK, observe the HO2S 2 display on the scan tool while moving the connectors and the wiring harnesses related to the sensor. A change in the HO2S 2 display will indicate the location of the fault. |
| • | If a DTC P0136 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance Heated Oxygen Sensor/Oxygen Sensor System Set . |
| • | An intermittent malfunction may be caused by fault in the HO2S circuit sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions . |
| • | Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems. |
The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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The Diagnostic System Check-Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step checks whether the malfunction is a high input condition.
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This step determines if the DTC P0136 is the result of a hard failure or an intermittent condition.
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In this step the DMM is used as a low current voltage source taking the place of the HO2S. If the HO2S 2 input circuit and the PCM are good, the scan tool will display aproximately 1,275 mV.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
Did you perform the Diagnostic System Check-Vehicle? | -- | Go to Step 2 | ||
Is the voltage more than the specified value? | 1050 mV | Go to Step 7 | Go to Step 3 | |
Does DTC P0136 set? | -- | Go to Step 4 | Go to Diagnostic Aids | |
Is the voltage more than the specified value? | 1125 mV | Go to Step 5 | Go to Step 6 | |
5 |
Does the test lamp illuminate? | -- | Go to Step 10 | Go to Step 9 |
6 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 |
7 |
Is the voltage within the specified value? | 35-55 mV | Go to Step 10 | Go to Step 8 |
8 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 |
9 | Repair the open in the HO2S 2 ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 12 | -- |
10 | Replace the HO2S 2.Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
12 |
Does the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 |
13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
