Code No. P0620: Alternator Control Circuit

OPERATION

When the ignition switch is turned ON, the current should be supplied from the engine-ECU connector terminal ALTL to the alternator connector terminal. When the engine starts under those conditions, the alternator should generate currents. The generated voltage is applied to the engine-ECU connector terminal ALTL from the alternator connector terminal. This allows the engine-ECU to detect that the electrical generation begins.
The engine-ECU connector terminal ALTG controls the alternator output voltage by turning the power transistor in the unit ON/OFF according to the electrical load.

FUNCTION

The engine-ECU compares the battery voltage with the voltage generated from the alternator to check whether the electrical generation is normal.

TROUBLE JUDGEMENT

Check Conditions

Ignition switch is in "ON" position.
The engine speed is 600 r/min or more.
The battery backup voltage is 13.5 V or more.
The G-terminal duty ratio is 10.2 % or more and 89.8 % or less.
The FR-terminal duty ratio is 80 % or less and the malfunction of P0622 is not detected.

Judgement Criterion

For 30 seconds, the final target generation voltage subtracted from the battery backup voltage equals 0.8 V or more.

For 30 seconds, the battery backup voltage subtracted from the final target generation voltage equals 1.3 V or more.

FAIL-SAFE AND BACKUP FUNCTION

Prohibits alternator output suppression control against current consumers. (operates as a normal alternator.)
The auto stop is prohibited.

PROBABLE CAUSES

Failed battery
Failed alternator & failed drive belt
Failed connector contact
Disconnection, short and damage of alternator G-terminal circuit
Disconnection, short and damage of alternator L-terminal circuit
Damage of battery backup circuit
Failed alternator
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Checking engine start conditions

Check whether the user uses the booster cable to start the engine.

note

This diagnosis code can be set due to the battery voltage drop.

Q. Have you ever used the booster cable to start the engine?

	Delete the diagnosis code and finish the check.

	Go to Step 2.

STEP 2. Check battery.

Check battery (Refer to GROUP 54A - Battery - On-vehicle Service - Battery Test ).

Q. Is the check result normal?

	Go to Step 3.

	Replace the battery.

STEP 3. Drive belt tension check

Drive belt tension check (Refer to GROUP 11E - On-vehicle Service - Drive Belt Tension Check and Adjustment )

Q. Is the check result normal?

	Go to Step 4.

	Replace the drive belt.

STEP 4. Check of damage in ALTG line between engine-ECU connector and alternator connector.

Q. Is the check result normal?

	Go to Step 5.

	Repair the connector(s) or wiring harness.

STEP 5. Check of damage in ALTL line between engine-ECU connector and alternator connector.

Q. Is the check result normal?

	Go to Step 6.

	Repair the connector(s) or wiring harness.

STEP 6. Check of damage in BACK line between battery and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 7.

	Repair the connector(s) or wiring harness.

STEP 7. M.U.T.-III diagnosis code.

Reconfirmation of diagnosis code.

Q. Is the diagnosis code set?

	Go to Step 8.

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

STEP 8. Replace the drive belt.

After replacing the drive belt, reconfirm whether the diagnosis code is set.

Q. Is the diagnosis code set?

	Go to Step 9.

	Check is end.

STEP 9. Replace the alternator.

After replacing the alternator, reconfirm whether the diagnosis code is set.

Q. Is the diagnosis code set?

	Replace the engine-ECU.

	Check is end.