Circuit Description
In order to control emissions of hydrocarbons (HC), of carbon monoxide (CO), and of oxides of nitrogen (NOx), a 3-way catalytic converter (TWC) is used. The catalyst within the converter promotes a chemical reaction that oxidizes the HC and the CO in the exhaust gases. The oxidation process converts 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 has the ability to monitor this process using the HO2S 1 and the HO2S 2. The HO2S 1 produces an output signal which indicates the amount of oxygen that is present in the exhaust gases entering the TWC converter. The HO2S 2 produces an output signal that indicates the oxygen storage capacity of the catalyst in the TWC converter. The oxygen storage capacity of the catalyst is an indicator of the converter's ability to convert exhaust gases efficiently. The HO2S 1 output signal is more active than the HO2S 2 output signal if the catalyst is operating efficiently.
Conditions for Running the DTC
| • | The engine speed is above 1,500 RPM. |
| • | The vehicle speed is between 32-80 km/h (20-50 mph). |
| • | The engine coolant temperature is equal to or more than 80°C (176°F). |
| • | The intake air temperature is between -10°C and +70°C (14°F-158°F). |
| • | The barometric pressure is more than 75 kPa. |
| • | The fuel tank level is above 25 percent. |
| • | The engine is running in the closed-loop mode. |
Conditions for Setting the DTC
The maximum HO2S 2 voltage is less than 600 mV for at least 8 minutes.
OR
| • | The minimum HO2S 2 voltage is at least 300 mV after a maximum voltage check during the fuel shut-off mode. |
| • | The above condition is present for 5 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles during which the diagnostic runs with the fault active. |
| • | The PCM records the operating conditions at the time that the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the DTC
| • | The MIL turns OFF after 3 consecutive trips during which the diagnostic runs and does not detect a fault. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the Clear DTC Information function of the scan tool, or disconnect the PCM battery feed in order to clear the DTC. |
Diagnostic Aids
Check for any of the following conditions:
| • | Inspect the exhaust system for leaks. Check the exhaust system between the 3-way catalytic converter and the flange for leaks, corrosion, loose hardware, and for missing hardware. Repair as necessary. |
| • | Misrouted HO2S wiring.The sensor pigtail may be misrouted and contacting the exhaust system, causing a fault in the sensor circuitry. |
| • | Inspect the HO2S 2 carefully for physical damage. Road hazards may damage the HO2S 2 because of the sensor's location under the vehicle chassis. |
| • | A shorted HO2S.An HO2S 2 that is shorted to ground or to voltage can set DTC P0136. Water contamination of the HO2S 2 can cause a short to occur in the sensor circuitry. A DTC P0136 that occurs more frequently when driving through standing water, or when operating the vehicle in wet conditions, can indicate water intrusion. Replace the HO2S 2 if the sensor is affected by moisture. |
| • | A faulty electrical connection between the HO2S 2 and the PCM |
An intermittent malfunction may be caused by a fault in the electrical circuit of the HO2S 2. Inspect the wiring harness and the components for any of the following conditions:
| • | Backed out terminals |
| • | Incorrect mating of terminals |
| • | Broken electrical connector locks |
| • | Incorrectly formed terminals or damaged terminals |
| • | Faulty terminal-to-wiring connections |
| • | Physical damage to the wiring harness |
| • | A broken wire inside the insulation |
| • | Corrosion of electrical connections, of splices, or of terminals |
If DTC P0136 cannot be duplicated, 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.
-
The Powertrain OBD System Check prompts the technician to complete some basic checks, and to save the applicable freeze frame data on the scan tool. This creates an electronic copy of the data that was taken when the fault occurred. The scan tool saves the information for later reference.
-
A cold HO2S 2 will read 1275 mV on a scan tool. The engine must be at normal operating temperature in order to continue diagnosis.
-
Review the Freeze Frame data in order to determine when the DTC set. Always record this information.
-
Normal voltage on the HO2S 2 signal circuit with the sensor disconnected is 4 to 5 volts. When the temperature of the HO2S 2 rises, the voltage will decrease and fluctuate between 100-900 megavolts.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
Did the HO2S 2 voltage start at the specified value and decrease less than the specified value while the engine warmed? | 1275 mV | |||
Is a DTC P0136 set? | -- | Go to Diagnostic Aids | ||
Is the HO2S 2 signal circuit voltage within the specified value? | 4-5 V | |||
5 |
Does the scan tool indicate HO2S 2 voltage below the specified value? | 100 mV | ||
6 |
Does the test lamp illuminate? | -- | ||
7 | Replace the HO2S 2. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | - | |
8 |
Was a repair necessary? | -- | ||
9 |
Was a repair necessary? | -- | ||
10 |
Was a repair necessary? | -- | ||
11 | Replace the PCM.. Is the action complete? | -- | - | |
12 |
Are any DTCs displayed on the scan tool? | -- | Go to the applicable DTC table | System OK |
