P0136
Heated Oxygen Sensor (HO2S) Circuit Sensor 2:
Heated Oxygen Sensor (HO2S) Circuit Sensor 2 (continued):
Heated Oxygen Sensor (HO2S) Circuit Sensor 2:
Circuit Description
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 them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The PCM has the ability to monitor this process using the HO2S 1 and the HO2S 2 heated oxygen sensors. The HO2S 1 sensor produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the three-way catalytic converter. The HO2S 2 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's 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 sensor.
Conditions for Running the DTC
^ Engine speed greater than 1500 RPM.
^ Vehicle speed greater than 32 km/h (20mph).
^ Engine coolant temperature greater than or equal to 50°C (122°F).
^ Intake air temperature is between -10°C (14°F) and 50°C (122°F).
^ Barometric pressure greater than 75 kPa.
^ Fuel tank level greater than 25%.
Conditions for Setting the DTC
^ Maximum voltage is less than 600mV.
^ In closed loop mode with the conditions met for 8 minutes.
Or
^ Minimum voltage greater than or equal to 300mV, after maximum voltage check and fuel shut-off mode.
^ The above condition is present for 5 seconds.
Action Taken When the DTC Sets
^ The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.
^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.
Conditions for Clearing the MIL/DTC
^ The MIL will turn "OFF" after three consecutively passing cycles without a fault present.
^ A History DTC will clear after 40 consecutive warm-up cycles without a fault.
^ DTC(s) can be cleared by using a scan tool or by disconnecting the PCM battery feed.
Diagnostic Aids
Check The Following Conditions:
^ Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection
^ Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the HO2S 2 display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the HO2S 2 display will indicate the location of the fault.
^ Exhaust system - Inspect the exhaust system for leaks. Check the exhaust between three way catalytic converter and flange for leaks, corrosion, or for loose or missing hardware and repair as necessary.
^ Follow DTC P0171 or P0172 for fuel system checks.
If DTC P0136 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
If any wiring repairs need to be made, Refer to Repair Procedures in Diagrams.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The Powertrain OBD System Check 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.
2. The scan tool will indicate 1275mV on the HO2S 2 parameter with a cold sensor. This is normal. The engine must be at normal operating temperature before continuing diagnosis.
3. Review Freeze Frame data to determine when the DTC set. Always record this information.
4. Normal voltage on the HO2S 2 signal circuit with the sensor disconnected is between 4 and 5 volts. As the temperature of the HO2S 2 rises the voltage will decrease and fluctuate between 100mV and 9OOmV.