Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Output Current Test
Required special tool: MB991502: Scan Tool MUT-II, MB991958: Scan Tool MUT-III Sub Assembly, MB991824: V.C.I., MB991827 MUT-III USB Cable, MB5991911: MUT-III Main Harness B. This test determines whether the generator outputs normal current. For best results, use a charging system tester. If not available, follow the steps below. See Fig 1 .
- Before the test, always be sure to check the following.
- Generator installation.
- Battery.
- Generator drive belt tension.
- Fusible link.
- Abnormal noise from the generator while the engine is running.
NOTE: The battery to be used should be slightly discharged. The load in a fully-charged battery will be insufficient and the test may not be able to be carried out correctly. - Turn the ignition switch to the LOCK (OFF) position.
- Disconnect the negative battery cable.
- Connect a clamp-type DC test ammeter with a range of 0-100A to the generator B terminal output wire.
- Connect a voltmeter with a range of 0-20V between the generator B terminal and ground. (Connect the positive lead of the voltmeter to the B terminal, and then connect the negative lead of the voltmeter to ground.)
- Connect the negative battery cable.
- Connect an engine tachometer or scan tool MB991958.
- Leave the hood open.
- Check to be sure that the reading on the voltmeter is equal to the battery positive voltage.
- After turning on the headlights, start the engine.
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- β’ You smell fuel, burning insulation, or see smoke.
- β’ Brakes feel soft, pull hard to one side, or make grinding noises.
- β’ The engine overheats, stalls repeatedly, or misfires under load.
- β’ You are missing required tools, torque specs, or safe lifting equipment.
- β’ You are not confident in the next step or safety outcome.
