P0038

DTC P0038: Heated Oxygen Sensor (rear) Heater 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 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 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.
Judgement Criterion

- The heated oxygen sensor (rear) heater current has continued to be higher than 10.5 ampere for 2 seconds.

FAIL-SAFE AND BACKUP FUNCTION

- None

OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 2 Monitors, Trips, Drive Cycles and Readiness Codes .

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)

- 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 D-35 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 - 8.0ohms [at 20°C (68°F)]

Q. Is the measured resistance between 4.5 and 8.0ohms [at 20°C (68°F)]?

YES Go to Step 2.

NO Replace the heated oxygen sensor (rear). Then go to Step 3.

STEP 2. 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 Monitors, Trips, Drive Cycles and Readiness Codes.

(2)Check the diagnostic trouble code (DTC).

Q. Is DTC P0038 set?

YES Replace the ECM (Refer to, Removal and Installation Removal and Replacement).
Then go to Step 3.
NO It can be assumed that this malfunction is intermittent. How to Cope With Intermittent Malfunctions.
STEP 3. 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 Monitors, Trips, Drive Cycles and Readiness Codes.

(2)Check the diagnostic trouble code (DTC).

Q. Is DTC P0038 set?

YES Retry the troubleshooting.
NO The inspection is complete.