The heated oxygen sensor (HO2S) bank 1 sensor 2 is threaded into
the cylinder 1, 3, 5 exhaust pipe behind the pre-converter (cylinders 1, 3 and 5 are
closest to the front of the dash). The sensor is an electrical source
that responds to oxygen content out of the pre-converter. When the sensor reaches
approximately 316°C (600°F), it produces a voltage based on the difference
in oxygen between the atmosphere and exhaust gas. The ECM sends a bias voltage (421-479 mV)
on the signal line, which is pulled up through high resistance. When the HO2S bank 1
sensor 2 is cold, it produces no voltage and has extremely high internal resistance.
The internal resistance of the sensor is much greater than the resistance of the bias
pull-up resistor. However, when the sensor heats up, it produces voltage that overrides
the bias voltage. This voltage is read by the ECM to determine the efficiency of the
catalytic converter. Under normal conditions, low sensor voltage means high oxygen
content/lean air-fuel mixture and vice versa. Normal sensor readings at steady cruise
with a properly functioning catalytic converter will be around 500-800 mV. DTC P0136
sets when the HO2S bank 1 sensor 2 signal voltage is too low for a certain
length of time.
DTC Parameters
DTC P0136 will set if HO2S bank 1 sensor 2 voltage is less than
40 mV when:
• | The condition exists for longer than 1 minute and 20 seconds. |
• | The HO2S bank 1 sensor 2 is in a closed loop. |
• | The Fuel level is greater than 10%. |
• | The calculated converter temperature is less than 940°C (1724°F). |
• | The commanded air/fuel ratio is 14.7 to 1. |
• | The Battery voltage is greater than 11.0 volts. |
• | There is no EVAP purge solenoid or the EVAP system DTCs have been set. |
DTC P0136 diagnostic runs continuously once the above conditions have
been met.
P0136 is a type B DTC
To locate an intermittent problem, use the scan tool to monitor the HO2S BANK 1
SENSOR 2 voltage with the engine idling at normal operating temperature. Wiggling
the wires while watching for a change in HO2S BANK 1 SENSOR 2 voltage
may locate the area where a short to ground in the wiring could lie.
Important: Do not apply grease or any material in the HO2S bank 1 sensor 2
harness connector or alter the wiring in any way. The wires carry air reference to
the sensor used to determine the difference in oxygen between the exhaust gas and
atmosphere.