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 TSBs, 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
Starting System Troubleshooting Chart
| Symptom | Possible Cause | Corrective Action |
|---|---|---|
| Engine will not crank | Dead battery | Check battery state of charge. Recharge if possible. Replace if necessary/td> |
| Melted fusible link | Replace fusible link | |
| Loose connections | Clean and tighten connections | |
| Key switch or start switch contacts in poor condition | Replace switch as necessary | |
| Solenoid hold-in coil open. Pull-in coil open or shorted. | Replace starter | |
| Solenoid contacts worn away | Replace starter | |
| Mechanical problem in engine | Check engine | |
| Engine cranks too slowly to start | Weak battery | Check battery. Recharge if possible. Replace if necessary |
| Loose or corroded connections | Clean and tighten connections | |
| Faulty starter | Test starter, Replace if necessary | |
| Starter spins, but engine will not crank | Faulty over-running clutch | Check over-running clutch, replace starter if necessary |
| Damaged or worn starter pinion gear or engine ring gear. | Check gears for damage or wear. Replace starter or ring gear |
Starting System inspection checklist
Begin with a thorough visual inspection of system and components
System tests:
Battery
- Load test
- Confirm charging system operation
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 voltage drop on the complete circuit
- If a problem is detected check the positive side and negative side separately to isolate problem
Check voltage at “KS” terminal on the starter with the ignition switch in the start position
- Typically 11.4-volt minimum (check vehicle service manual for correct specification)
System voltage drop test
The diagram shows a carbon pile tester. Test can be done with electronic system tester, follow instructions included with the tool.
Subtract (-) VM B from VM A. Loss not to exceed 0.5V.
Proceed to positive & negative cable. Voltage loss tests if total loss exceeds specs.
Positive side voltage drop test
Test can be performed with:
- Electronic tester
- Carbon pile load tester
- Cranking engine (If cranking engine)
- Disable the fuel or ignition system to keep the engine from starting during the test
- DO NOT crank the engine for longer than 10 seconds at a time
- Wait a minimum of 60 seconds before cranking engine again to cool the starter
Ground side voltage drop test
Test can be performed with:
- Electronic tester
- Carbon pile load tester
- Cranking engine (If cranking engine)
- Disable the fuel or ignition system to keep the engine from starting during the test
- DO NOT crank the engine for longer than 10 seconds at a time
- Wait a minimum of 60 seconds before cranking engine again to cool the starter