Mitsubishi Lancer IX (CS) 1.6 4G18 (2003): Charging Circuit Voltage Drop Test

Part numbers are from the manufacturer's original catalogue. Check them against your VIN before ordering.

• digital multimeter (DC voltmeter)
• DC clamp meter or ammeter
• 10 mm and 12 mm wrenches
• battery terminal brush
• tachometer or RPM monitoring via the instrument cluster

1. Check the starting condition. The battery must be charged, and the terminals and cable ends must be clean and tight. The alternator belt must not slip or have cracks. If the battery is badly discharged, charge it first. Otherwise the alternator will run at its maximum output current and the result will be skewed.
2. Shut off the engine and turn off all electrical loads. Check that the positive stud of the alternator B terminal (the thick cable with a nut on the rear housing) has no corrosion and that the nut is not loose. Tighten the nut with moderate force, without stripping the threads. For an M8 stud, a guideline is about 8-12 N·m (6-9 lb-ft); the exact value is in the manufacturer's service manual.
3. Connect the voltmeter. Put the positive probe on the alternator B terminal (on the stud, not on the insulation) and the negative probe on the battery positive post. Use secure clips so the probes do not come off while the engine is running. Set the meter to DC voltage, on its most sensitive range (a few volts).
4. Connect the DC clamp meter around the cable from the alternator B terminal. If you do not have a clamp meter, you can estimate the current from the loads that are switched on. However, measuring the current directly is more accurate.
5. Start the engine and hold it at about 2500 rpm. Turn on the low or high beams, the rear window defogger, the heater blower at maximum and other high-power loads. The goal is a load current of about 20-30 A. Take readings when the current is stable.
6. Read the voltage on the voltmeter. Normal: a drop of no more than 0.3 V at a current of about 30 A (a reference value from Mitsubishi service practice; at a different current the value changes proportionally). If the drop is higher than normal, there is extra resistance in the power circuit.
7. Locate the point of the loss. Move the negative probe from the battery positive post to the cable end itself and to the battery terminal, then to the alternator B terminal past the nut. This shows where the voltage is being "lost": at the battery connection, in the cable itself or at the connection at the alternator.
8. Also check the ground circuit in the same way. Put one probe on the alternator housing and the other on the battery negative post, at the same rpm and load. The drop should be very small, with a guideline of no more than 0.1-0.2 V. A higher value points to a poor body or engine ground.
9. Fix the cause. Remove the battery terminals, clean the seating surfaces and cable ends with a brush, apply conductive grease to the contacts and tighten them. If the cable is damaged (blackened insulation, green corrosion under the terminal, melting), replace the whole cable instead of repairing it by twisting the wires together.
10. Repeat the measurement following steps 3-6. After the fault is fixed, the drop should fall within the normal range. Then separately check the charging voltage at the battery terminals. At about 2500 rpm and without a heavy load, it should be about 13.8-14.7 V.

• Before disconnecting any power cables, disconnect the battery negative terminal
• When connecting the probes, do not let the B terminal short to ground
• This is a power cable with no fuse on the section before the fusible link
• Keep probes, clothing and tools away from the belt and fan while the engine is running
• Do not disconnect a battery terminal with the engine running, because the voltage spike can damage the engine control unit and the regulator
• If the charging voltage is still outside the 13.8-14.7 V range after the voltage losses are fixed, the alternator itself or its regulator is faulty
• In that case, test the unit separately on a test bench