[Previous][Next]
DTC P0037: Heated Oxygen Sensor (rear) Heater Control Circuit Low
 
 
 
 
CIRCUIT OPERATION
  • Power is supplied from the MFI relay to the heated oxygen sensor (rear) heater.
  • The ECM terminal OHRL controls continuity to the heated oxygen sensor (rear) heater by turning the power transistor in the ECM "ON" and "OFF".
 
 
TECHNICAL DESCRIPTION
  • The ECM checks whether the heater current is within a specified range when the heater is energized.
  • The ECM checks whether the heater voltage is within a specified range when the heater is not energized.
 
 
DESCRIPTIONS OF MONITOR METHODS
  • Heated oxygen sensor (rear) heater current or voltage is out of specified range.
 
 
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)
  • Not applicable
Sensor (The sensor below is determined to be normal)
  • Not applicable
 
 
DTC SET CONDITIONS
Logic Flow Chart
 
 
Check Conditions
  • More than 2 seconds have passed since the engine starting sequence was completed.
  • While the heated oxygen sensor (rear) heater is on.
  • Battery positive voltage is between 11 and 16.5 volts.
Judgment Criterion
  • The heated oxygen sensor (rear) heater current has continued to be lower than 0.17 ampere for 2 seconds.
Check Conditions
  • More than 2 seconds have passed since the engine starting sequence was completed.
  • While the heated oxygen sensor (rear) heater is off.
  • Battery positive voltage is between 11 and 16.5 volts.
Judgment Criterion
  • The heated oxygen sensor (rear) heater voltage has continued to be lower than 2.0 volts for 2 seconds.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • None
 
 
OBD-II DRIVE CYCLE PATTERN
  • Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 2 .
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be stored are: )
  • Open or shorted heated oxygen sensor (rear) heater circuit, harness damage, or connector damage.
  • Heated oxygen sensor (rear) heater failed.
  • ECM failed.

 
 
DIAGNOSIS
Required Special Tools:
  • MB991658: Test Harness
  • MB992110: Power Plant ECU Check Harness
STEP 1. Check the heated oxygen sensor (rear).
(1) Disconnect heated oxygen sensor (rear) connector and connect test harness special tool, MB991658, to the connector on the heated oxygen sensor (rear) side.
(2) Measure the resistance between heated oxygen sensor connector terminal power supply line and terminal OHRL line.
(3)
Standard value: 4.5 - 8.0 ohms [at 20°C (68°F)]
Is the measured resistance between 4.5 and 8.0 ohms [at 20°C (68°F)]?
Go to Step 2.
Replace the heated oxygen sensor (rear). Then go to Step 8.
 
STEP 2. Measure the power supply voltage at heated oxygen sensor (rear) harness side connector.
(1) Disconnect the heated oxygen sensor (rear) connector and measure at the harness side.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal power supply line and ground.
  • Voltage should be battery positive voltage.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 3.
Repair or replace the connector(s), or check and repair the harness of short to ground and open circuit in power supply line between MFI relay connector and heated oxygen sensor (rear) connector. Then go to Step 8.
 
STEP 3. Measure the power supply voltage at ECM connector by using power plant ECU check harness special tool MB992110.
(1) Disconnect all ECM connectors. Connect the power plant ECU check harness special tool MB992110 between the separated connectors.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal OHRL and ground.
  • Voltage should be battery positive voltage.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 5.
Go to Step 4.
 
STEP 4. Check of short to ground and open circuit in OHRL line between heated oxygen sensor (rear) connector and ECM connector.
Is the harness wire in good condition?
Replace the ECM (Refer to Removal and Installation ). Then go to Step 8.
Repair it. Then go to Step 8.
 
STEP 5. Check of harness damage in power supply line between MFI relay connector and heated oxygen sensor (rear) connector.
Is the harness wire in good condition?
Go to Step 6.
Repair it. Then go to Step 8.
 
STEP 6. Check of harness damage in OHRL line between heated oxygen sensor (rear) connector and ECM connector.
Is the harness wire in good condition?
Go to Step 7.
Repair it. Then go to Step 8.
 
STEP 7. Check the trouble symptoms.
(1) Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 2 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0037 stored?
Replace the ECM (Refer to Removal and Installation ). Then go to Step 8.
It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .
 
STEP 8. Test the OBD-II drive cycle.
(1) Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 2 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0037 stored?
Retry the troubleshooting.
The inspection is complete.