P0038

DTC P0038: Heated Oxygen Sensor Heater Control Circuit High (sensor 2)

Heated Oxygen Sensor (Rear) Heater Circuit Part 1:

Heated Oxygen Sensor (Rear) Heater Circuit Part 2:

CIRCUIT OPERATION
- Power is supplied from the MFI relay (terminal No. 3) to the heated oxygen sensor (rear) heater.
- The ECM or the PCM (terminal No. 18) controls continuity to the heated oxygen sensor (rear) heater by turning the power transistor in the ECM or the PCM "ON" and "OFF".

TECHNICAL DESCRIPTION
- The ECM or the PCM 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)
- Engine coolant temperature sensor

DTC SET CONDITIONS

Logic Flow Chart:

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.

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 2 OBD-II Drive Cycle Pattern Lists.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Open or shorted heated oxygen sensor (rear) heater circuit, harness damage or connector damage.
- Open circuit in heated oxygen sensor (rear) heater.
- ECM failed.
- PCM failed.

DIAGNOSIS

Required Special Tool:
- MB991658: Test Harness

STEP 1. Check the heated oxygen sensor (rear).

1. Disconnect heated oxygen sensor (rear) connector D-34 and connect test harness special tool, MB991658, to the connector on the heated oxygen (rear) sensor side.

2. Measure the resistance between heated oxygen sensor connector terminal No. 1 and terminal No. 3.
Standard value: 11 - 18 Ohms [at 20 degrees C (68 degrees F)]

Q: Is the measured resistance between 11 and 18 Ohms [at 20 degrees C (60 degrees 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 OBD-II Drive Cycle Pattern Lists.
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0038 set?

YES: Replace the ECM or the PCM. Then go to Step 3.

NO: It can be assumed that this malfunction is intermittent.

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 OBD-II Drive Cycle Pattern Lists.
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0038 set?

YES: Retry the troubleshooting.

NO: The inspection is complete.