2. Abnormal Voltage Output of Heated Oxygen Sensor (DTC P0136 and P0156)
While the ECM is performing active air fuel ratio control, the air fuel ratio is forcibly regulated to become rich or lean. If the sensor is not
functioning properly, the voltage output variation is small. For example, when the heated oxygen sensor voltage does not decrease to less than
0.21 V or does not increase to more than 0.59 V during active air fuel ratio control, the ECM determines that the sensor voltage output is
abnormal and sets DTCs P0136 or P0156.
3. Open or Short in Heated Oxygen Sensor Circuit (DTCs P0137 and P0157 or P0138 and P0158)
During active air fuel ratio control, the ECM calculates the oxygen storage capacity* of the three-way catalytic converter by forcibly
regulating the air fuel ratio to become rich or lean.
If the heated oxygen sensor has an open or short, or the voltage output of the sensor noticeably decreases, the oxygen storage capacity
indicates an extraordinarily high value. Even if the ECM attempts to continue regulating the air fuel ratio to become rich or lean, the heated
oxygen sensor output does not change.
While performing active air fuel ratio control, when the target air fuel ratio is rich and the heated oxygen sensor voltage output is 0.21 V or
less (lean), the ECM interprets this as an abnormally low sensor output voltage and sets DTC P0137 or P0157. When the target air fuel ratio is
lean and the voltage output is more than 0.59 V (rich) during active air fuel ratio control, the ECM determines that the sensor voltage output is
abnormally high, and sets DTC P0138 or P0158.
HINT
DTC P0138 or P0158 is also set if the heated oxygen sensor voltage output is more than 1.2 V for 10 seconds or more.
*: The three-way catalytic converter has the capability to store oxygen. The oxygen storage capacity and the emission purification
capacity of the three-way catalytic converter are mutually related. The ECM determines whether the catalyst has deteriorated,
based on the calculated oxygen storage capacity value See: P0420.
No comments:
Post a Comment