DTC P0137: Heated Oxygen Sensor Circuit Low Voltage (sensor 2)

CIRCUIT OPERATION
• A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM (terminal No. 75) <M/T> or PCM (terminal No. 73) <A/T> from the output terminal (terminal No. 1) of the heated oxygen sensor (rear).
• Terminal No. 2 of the heated oxygen sensor (rear) is grounded with ECM (terminal No. 92) <M/T> or PCM (terminal No. 57) <A/T>.
TECHNICAL DESCRIPTION
• The output signal of the heated oxygen sensor (front) is compensated by the output signal of the heated oxygen sensor (rear).
• The ECM <M/T> or PCM <A/T> checks for an open circuit in the heated oxygen sensor (rear) output line.
DESCRIPTIONS OF MONITOR METHODS
• The output of the heated oxygen sensor (rear) is monitored when the air-fuel mixture is forcefully made richer, and if the sensor output remains low and unchanged, a malfunction is determined to have occurred.
MONITOR EXECUTION
Continuous
MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
• Heated oxygen sensor heater (front) monitor
• Heated oxygen sensor heater (rear) monitor
• Air/fuel ratio feedback monitor

Sensor (The sensor below is determined to be normal)
• Volume air flow sensor
• Engine coolant temperature sensor
• Intake air temperature sensor
• Barometric pressure sensor
DTC SET CONDITIONS Logic Flow Chart


Check Conditions
After 2 seconds or more pass from the rime when the monitor determines normally for detection an open circuit.
Heated oxygen sensor (rear) signal voltage has continued to be 0.15 volt or lower.
Engine coolant temperature is higher than 76°C (169°F).
Engine speed is higher than 1,200 r/min.
Volumetric efficiency is higher than 25 percent.
Volume airflow sensor output frequency is 81 Hz or more.
At least 20 seconds have passed since fuel shut off control was canceled.
The heated oxygen sensor (front) outputs 0.5 volt or more.
After the ignition switch is turned ON, the changes in the output voltage of the heated oxygen sensor (rear) is lower than 0.078 volt.
Monitoring time: 8 seconds.

Judgement Criterion
• Making the air/fuel ratio 15 percent for 8 seconds richer does not result in raising the heated oxygen sensor (rear) output voltage beyond 0.15 volt.
OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 11 .
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:
• Heated oxygen sensor (rear) failed.
• Short circuit in heated oxygen sensor (rear) output line.
• ECM failed. <M/T>
• PCM failed. <A/T>