Code No. P0622: Alternator FR Terminal System

OPERATION

The energized state of the alternator field coil is inputted from the alternator (terminal No. 4) to the engine-ECU (terminal No. 54).

FUNCTION

A signal of the power supply duty ratio for the alternator field coil is inputted to the engine-ECU.
In response to the signal, the engine-ECU detects the alternator output current and controls the idling speed according to the output current (electric load).

TROUBLE JUDGMENT

Check Condition

Engine speed is 50 r/min or higher.

Judgment Criterion

Input voltage from the alternator FR terminal has continued to be approximately battery positive voltage for 20 seconds.

PROBABLE CAUSES

Failed alternator
Open/short circuit and damage in alternator FR terminal circuit or loose connector
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: A-127 alternator connector

Q. Is the check result normal?

Go to Step 2 .

Repair or replace the connector.

STEP 2. Perform voltage measurement at A-127 alternator connector.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal No. 4 and earth.

OK: System voltage

Q. Is the check result normal?

Go to Step 6 .

Go to Step 3 .

STEP 3. Connector check: A-34 engine-ECU connector.

Q. Is the check result normal?

Go to Step 4 .

Repair or replace the connector.

STEP 4. Check harness between A-127 (terminal No. 4) alternator connector and A-34 (terminal No. 54) engine-ECU connector.

Check output line for open/short circuit.

Q. Is the check result normal?

Go to Step 5 .

Repair the damaged harness wire.

STEP 5. M.U.T.-III diagnosis code.

Reconfirmation of diagnosis code.

Q. Is the diagnosis code set?

	Replace the engine-ECU then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding ).

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

STEP 6. Perform voltage measurement at A-34 engine-ECU connector.

Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB991987), and then measure the voltage on the check connector.
Engine: Idle after warm-up
Transmission: Neutral
Cooling fan: Inactive
Voltage between terminal No. 54 and earth.

OK: Switching the headlamps to ON from OFF causes the voltage to fall.

Q. Is the check result normal?

Go to Step 7 .

Go to Step 5 .

STEP 7. Check harness between A-127 (terminal No. 4) alternator connector and A-34 (terminal No. 54) engine-ECU connector.

Check output line for damage.

Q. Is the check result normal?

Go to Step 8 .

Repair the damaged harness wire.

STEP 8. M.U.T.-III diagnosis code.

Reconfirmation of diagnosis code.

Q. Is the diagnosis code set?

	Replace the alternator.

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