Code No. P0038: Oxygen Sensor (rear) Heater Circuit High Input

OPERATION

Power is supplied to the heater power terminal of the oxygen sensor (rear) connector from the engine control relay connector terminal.
The heater the oxygen sensor (rear) connector terminal is controlled by the power transistor in the engine-ECU connector terminal OHRL.

FUNCTION

The power supply to the oxygen sensor (rear) heater is controlled by the ON/OFF control of the power transistor in the engine-ECU.
Heating the oxygen sensor (rear) heater enables the oxygen sensor (rear) to provide good response even when the exhaust emission temperature is low.

TROUBLE JUDGMENT

Check Conditions

More than 2 seconds have passed since the engine starting sequence was completed.
While the oxygen sensor (rear) heater is on.
Battery positive voltage is more than 11 V and is less than 16.5 V.

Judgement Criterion

The oxygen sensor (rear) heater current is more than 10.5 A for 2 seconds.

FAIL-SAFE AND BACKUP FUNCTION

None

PROBABLE CAUSES

Failed oxygen sensor (rear) heater
Short circuit in oxygen sensor (rear) heater circuit or loose connector contact
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Perform resistance measurement at oxygen sensor (rear) connector.

Oxygen sensor (rear) connector check.
Disconnect connector, and measure at sensor side.
Resistance between terminal power supply line and engine-ECU OHRL line.

OK: 4.5 - 8.0 Ω (at 20°C)

Q. Is the check result normal?

	Go to Step 2.

	Repair or replace the connector, or replace the oxygen sensor (rear).

STEP 2. Check harness between engine control relay connector terminal and oxygen sensor (rear) connector terminal.

Check power supply line for short circuit.

Q. Is the check result normal?

	Go to Step 3.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 3. Check harness between oxygen sensor (rear) connector terminal and engine-ECU connector terminal OHRL.

Check earthing line for short circuit.

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 4. M.U.T.-III diagnosis code

Reconfirmation of diagnosis code.

Q. Is diagnosis code set?

	Replace the engine-ECU.

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).