System Diagnosis

Proper vehicle diagnosis requires a plan before you start

Following a set procedure to base your troubleshooting on will help you find the root cause of a problem and prevent unnecessary repeat repairs .

STEP ONE: Understand the Customer’s Concern

• Information collection beyond the basics.
• Questions asked MUST be related To the system you will be working on and the customer complaint

STEP TWO: Check for Technical Service Bulletins

• Every vehicle that comes into the shop for a repair (not necessary for routine maintenance) should be checked for TSB’s , This can save you hours of troubleshooting.

STEP THREE: Conduct a Systematic Diagnosis

This step will be different for every system

• Follow the troubleshooting steps for the system you are working on.
• Make sure to check EVERY component of the system and that they are in proper working order.
• Document your diagnosis including tests and results.

STEP FOUR: Complete and Confirm the Repair

• Make sure you have taken care of the customers concerns.
• Try to duplicate the conditions that were present when the vehicle failed.

Charging System Troubleshooting Chart

System Diagnosis

Begin with a thorough visual inspection of system and components

System tests:

Battery

• Load test

Alternator drive belt

• Belt condition
• Alignment
• Proper tension

System cables & wires

• Make sure all connections are clean and tight
• Check wires for fraying, insulation damage, and other physical damage

Voltage drop test

• Check positive side of the charging circuit. (0.2 volts of less)
• Check negative side of the charging circuit. (0.2 volts or less)
• High voltage drop indicates poor connections or damaged cables

Alternator Output test

• Start vehicle and adjust engine speed to approximately 2,000RPM
• Check voltage at alternator and at battery voltage should be between 13 and 15 volts
• Turn on vehicle loads (headlights, blower motor, defrosters) and repeat test
• Refer to vehicle service manual for correct specifications

Voltage drop test positive side

• Attach your meter's positive lead to the alternator output stud and your negative lead to battery positive post.
• Run engine at 2,000 RPM with the lights, blower motor, and radio on, the reading on meter, should be less than .2 volts

Voltage drop test negative side

• Attach your meter's negative lead on the alternator case, or ground strap if equipped, and the positive lead on the battery negative post.
• Run the engine at 2,000 RPM with the lights, blower motor, and radio on, the reading on your meter should be .2 volts or less.