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 or engine-A-M/T-ECU (terminal No. 54).

FUNCTION

A signal of the power supply duty ratio for the alternator field coil is inputted to the engine-ECU or engine-A-M/T-ECU.
In response to the signal, the engine-ECU or engine-A-M/T-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 or shorted alternator FR terminal circuit, harness damage, or connector damage
Failed engine-ECU or engine-A-M/T-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-08 engine-ECU connector or engine-A-M/T-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-08 (terminal No. 54) engine-ECU connector or engine-A-M/T-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 or engine-A-M/T-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-08 engine-ECU connector or engine-A-M/T-ECU connector.

Disconnect engine-ECU connector or engine-A-M/T-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
Radiator 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-08 (terminal No. 54) engine-ECU connector or engine-A-M/T-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 ).