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DTC P0038: Heated Oxygen Sensor (rear) Heater Control Circuit High
 
 
 
 
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.
 
 
DESCRIPTIONS OF MONITOR METHODS
  • Heated oxygen sensor heater (rear) current is out of specified range.
 
 
MONITOR EXECUTION
  • Continuous
 
 
MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)
Other Monitor (There is no temporary DTC set 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 power supply mode of the electric motor switch was ON.
  • While the heated oxygen sensor (rear) heater is on.
  • 12V starter battery positive voltage is between 11 and 16.5 volts.
Judgment Criterion
  • The heated oxygen sensor (rear) heater current has continued to be higher than 10.5 amperes for 2 seconds.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • None.
 
 
OBD-II DRIVE CYCLE PATTERN
  • Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 1 .
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
  • Shorted heated oxygen sensor (rear) heater circuit or connector damage.
  • Heated oxygen sensor (rear) failed.
  • ECM failed.

 
 
DIAGNOSIS
Required Special Tool:
  • MB991658: Test 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.
(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 5.
 
STEP 2. Check of short circuit to power supply in power supply line between MFI relay connector and heated oxygen sensor (rear) connector.
Is the harness wire in good condition?
Go to Step 3.
Repair the connector(s) or wiring harness. Then go to Step 5.
 
STEP 3. Check of short circuit to power supply in OHRL line between heated oxygen sensor (rear) connector and ECM connector.
Is the harness wire in good condition?
Go to Step 4.
Repair the connector(s) or wiring harness. Then go to Step 5.
 
STEP 4. Check the trouble symptoms.
(1) Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 1 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0038 set?
Replace the ECM (Refer to Removal and Installation ). Then go to Step 5.
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 5. 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 1 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0038 set?
Retry the troubleshooting.
The inspection is complete.