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DTC P0038: Heated Oxygen Sensor (rear) Heater Control Circuit High

 
 
 
 
CIRCUIT OPERATION
  • Power is supplied from the MFI relay (terminal No. 2) to the heated oxygen sensor (rear) heater.
  • The ECM (terminal No. 35) 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 (rear) heater current 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 is more 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 2 .
 
 
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) heater failed.
  • ECM failed.

 
 
DIAGNOSIS
Required Special Tools:
  • MB991958: Scan Tool (M.U.T-III Sub Assembly)
    • MB991824: V.C.I.
    • MB991827: USB Cable
    • MB991910: Main Harness A
  • MB991658: Test Harness
STEP 1. Check harness connector D-38 at heated oxygen sensor (rear) for damage.
Is the harness connector in good condition?
Go to Step 2.
Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 8.
 
STEP 2. Check the heated oxygen sensor (rear).
(1) Disconnect heated oxygen sensor (rear) connector D-38 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 No. 1 and terminal No. 2.
(3)
Standard value: 4.5 - 8.0 Ω [at 20°C (68°F)]
Is the measured resistance between 4.5 and 8.0 Ω [at 20°C (68°F)]?
Go to Step 3.
Replace the heated oxygen sensor (rear). Then go to Step 8.
 
STEP 3. Check harness connector A-37X at MFI relay for damage.
Is the harness connector in good condition?
Go to Step 4.
Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 8.
 
STEP 4. Check for short circuit to power supply between MFI relay connector A-37X (terminal No. 2) and heated oxygen sensor (rear) connector D-38 (terminal No. 1).
Is the harness wire in good condition?
Go to Step 5.
Repair it. Then go to Step 8.
 
STEP 5. Check harness connector B-26 at ECM for damage.
Is the harness connector in good condition?
Go to Step 6.
Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 8.
 
STEP 6. Check for short circuit to power supply between heated oxygen sensor (rear) connector D-38 (terminal No. 2) and ECM connector B-26 (terminal No. 35).
noteCheck harness after checking intermediate connectors A-17 and C-28. If intermediate connector is damaged, repair or replace them. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 8.
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 P0038 set?
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 P0038 set?
Retry the troubleshooting.
The inspection is complete.