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 customer’s concerns.
- Try to duplicate the conditions that were present when the vehicle failed.
Charging System Troubleshooting Chart
|Symptom||Possible Cause||Corrective Action|
|Batteries not charging||Insufficient belt tension, worn belt||Tighten or replace|
|Defective battery(s) or battery connections||Check battery and battery terminal connections|
|Blown fuse or fusible link||Check fuse and fusible link; replace as needed|
|Defective wiring||Check voltage drop|
|Faulty alternator||Replace alternator|
|Excessive electrical load||Reduce load by turning off all unnecessary accessories|
|Constantly overcharging (battery electrolyte is depleted in a short time)||Battery||Faulty battery; replace|
|Poor contact at voltage detection point of alternator||Clean contact area|
|Faulty voltage regulator||Replace alternator|
|Abnormal Noise||Insufficient belt tension||Tighten or replace|
|Faulty bearing||Replace alternator|
Begin with a thorough visual inspection of system and components
- Load test
Alternator drive belt
- Belt condition
- 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.