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) 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).
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 checks for an open circuit in the heated oxygen sensor (rear) output line.
DTC SET CONDITIONS

Check Conditions
3 minutes or more have passed since the starting sequence was completed.
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 56 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: 10 seconds.

Judgement Criteria
• Making the air/fuel ratio 15 percent richer for 10 seconds does not result in raising the heated oxygen sensor (rear) output voltage beyond 0.15 volt.
• The ECM monitors for this condition once during the drive cycle.
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.
• Connector damage.
• ECM failed.