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

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 check list

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 problem is detected check positive side and negative side separately to isolate problem
Check voltage at “KS” terminal on starter with ignition switch in the start position
  • Typically 11.4 volt minimum (check vehicle service manual for correct specification)

System voltage drop test

Diagram shows a carbon pile tester. Test can be done with electronic system tester, follow instruction included with tool.

System voltage drop test
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

Positive side voltage drop test

Test can be performed with:

  • Electronic tester
  • Carbon pile load tester
  • Cranking engine (If cranking engine)
    1. Disable the fuel or ignition system to keep the engine from starting during the test
    2. DO NOT crank the engine for longer than 10 seconds at a time
    3. Wait a minimum of 60 seconds before cranking engine again to cool the starter

Ground side voltage drop test

Positive side voltage drop test

Test can be performed with:

  • Electronic tester
  • Carbon pile load tester
  • Cranking engine (If cranking engine)
    1. Disable the fuel or ignition system to keep the engine from starting during the test
    2. DO NOT crank the engine for longer than 10 seconds at a time
    3. Wait a minimum of 60 seconds before cranking engine again to cool the starter
 

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