P0136
DTC P0136 Heated Oxygen Sensor (HO2S) Circuit - Sensor 2 (1 Of 2):
DTC P0136 Heated Oxygen Sensor (HO2S) Circuit - Sensor 2 (2 Of 2):
Heated Oxygen Sensor (HO2S) Circuit:
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 ECM 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 SETTING THE DTC
- Voltage average is less than 120mV or greater than 9OOmV.
- Engine speed greater than 1600 RPM.
- Engine coolant temperature greater than or equal to 70°C (158°F).
- Barometric pressure greater than 75 kPa.
- Fuel tank level greater than 15%.
- In closed loop mode with the above conditions meet for 3 minutes.
Or
- Pull-up voltage greater than 4.5V for 2 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 ECM 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 consecutive drive cycles without a fault present.
- A 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 ECM battery feed.
DIAGNOSTIC AIDS
Check the following conditions:
- Poor connection at ECM. Inspect harness connectors for backed out terminal, 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.
- After all checks have been completed and malfunction continues, replace the ECM with a known good unit and retest.
If DTC P0136 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions since the DTC was last set. This may assist in determining how often the DTC sets.
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 Engine 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. If the HO2S 2 voltage is greater than 1V, check for a short to voltage in the HO2S 2 signal circuit.
3. Review Freeze Frame data to determine when the DTC set. Always record this information.
4. The HO2S sensor 2 may be shorted to ground, if so the voltage value displayed in the values column may not change, if so check for a short to ground in the HO2S sensor 2 signal circuit.