1. Starting System Circuit Operation and Testing
Unit 4
Starting System Circuit Operation and Testing

2. Introduction Almost every system relies on: Automobiles have:
12-volt storage battery
Electrical and electronic components
Engine starting system
Electrical charging system
Electronic control modules
Networking systems

3. Engine Starting Systems— Starter Draw Testing (1 of 3)
Testing is a good indicator of overall starter motor performance.
Perform tests with fully charged and correct capacity battery.
Can be tested in two ways
On vehicle—starter draw test
Off vehicle—no-load test

4. Engine Starting Systems— Starter Draw Testing (2 of 3)
Test current draw under load.
Easier while motor mounted in the vehicle
Draw highest when starter pinion gear first engages with flywheel
As starter motor and engine cranking speed increase, current draw decreases and stabilizes.

5. Engine Starting Systems— Starter Draw Testing (3 of 3)
Variety of equipment used, but should have:
Inductive high-current ammeter—measure cranking current flow
Voltmeter—measure cranking voltage
Disabled engine should crank but not start.
Measure current flow, voltage during cranking.

6. Engine Starting Systems—Testing Starter Circuit Voltage Drop (1 of 5)
Electrical circuit
Control circuit
High-current circuit
Activates solenoid
Battery
Either PCM controlled or non-PCM controlled
Main battery cables
Solenoid contacts
Heavy ground cables

7. Engine Starting Systems—Testing Starter Circuit Voltage Drop (2 of 5)
High-current circuit susceptible because of larger amount of current
Starter must be activated by the solenoid.
Starter must click when ignition is engaged.
If no click, test control side of starter circuit.

8. Engine Starting Systems—Testing Starter Circuit Voltage Drop (3 of 5)
Use voltmeter or DVOM to measure drop on all circuit parts.
Voltmeter with minimum/maximum range is useful.
Records and holds maximum voltage drop for particular operation cycle
Keep circuits under load.

9. Engine Starting Systems—Testing Starter Circuit Voltage Drop (4 of 5)
DVOM connected in parallel across component or circuit part being tested
Test large sections first, then individual components to locate drop.
Check specifications, but usually no more than 0.5 volts for a 12-volt circuit.

10. Engine Starting Systems—Testing Starter Circuit Voltage Drop (5 of 5)
Perform same test on positive side of circuit.
Starter cable connected to input of solenoid
Output connected to input of starter motor
Measure drop from positive battery post to starter motor input.
Disable engine.

11. Engine Starting Systems—Inspecting/Testing the Starter Control Circuit (1 of 4)
Made up of:
Battery
Fusible link
Ignition switch
Neutral safety switch
Clutch switch starter relay
Solenoid windings

12. Engine Starting Systems—Inspecting/Testing the Starter Control Circuit (2 of 4)
If controlled by PCM, understand all circuits.
Before performing tests, confirm customer’s issues.
Consult manufacturer diagrams for circuit operation.
Identify all components.

13. Engine Starting Systems—Inspecting/Testing the Starter Control Circuit (3 of 4)
First test with DVOM.
Place red lead on starter input terminal.
Place black lead on starter housing.
Measure voltage with key in crank position.
Faulty if less than 10.5 volts at control circuit

14. Engine Starting Systems—Inspecting/Testing the Starter Control Circuit (4 of 4)
If faulty, voltage drop test on power side:
If less than 0.5, measure starter ground circuit.
If excessive, do individual voltage drops on ground leg.
If both within specs, measure resistance of solenoid pull-in and hold-in windings.

15. Engine Starting Systems—Inspecting/Testing Relays, Solenoids (1 of 5)
Before any tests:
Ensure battery is charged and in good condition.
Check wiring diagrams to determine:
Circuit operation
Identification
Location of all components

16. Engine Starting Systems—Inspecting/Testing Relays, Solenoids (2 of 5)
Test 1—measure relay winding resistance
If out of specs, needs replacement
Relay okay, test contacts for voltage drop.
Use adapter between the relay and relay socket.
Lab test—on relays with suppression diode in parallel with a relay winding

17. Engine Starting Systems—Inspecting/Testing Relays, Solenoids (3 of 5)
Solenoids difficult to test, with poor access
Limited to voltage and voltage drop tests on main contacts
For other tests, starter motor may need to be removed; for example:
Pull-in test
Hold-in winding test

18. Engine Starting Systems—Inspecting/Testing Relays, Solenoids (4 of 5)
Voltage drop test across solenoid contacts
Place red lead on solenoid B-positive input.
Place black lead on solenoid B-positive output.
Voltage drop should be less than 0.5 volts.
If not, replace starter assembly.

19. Engine Starting Systems—Inspecting/Testing Relays, Solenoids (5 of 5)
Solenoid winding testing—must partially disassemble solenoid
Disconnect control circuit connector from solenoid.
If solenoid and starter operate, likely a fault in the control circuit
If solenoid or starter does not work, starter faulty

20. Engine Starting Systems—Removing and Installing a Starter
Usually located close to flywheel end of engine
May need to remove components or covers for access
Often more easily reached from under the vehicle
Always disconnect negative battery lead first.

21. Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (1 of 7)
Slow cranking:
Example, electrical fault: High resistance in solenoid contacts
Replace starter.
Example, mechanical engine fault: Spin main bearing causing drag on crankshaft
Rebuild entire engine.

22. Typical electrical problems:
Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (2 of 7)
Typical electrical problems:
Loose, dirty, or corroded terminals and connectors
Discharged or faulty battery
Faulty starter motor
Faulty control circuits

23. Typical mechanical problems:
Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (3 of 7)
Typical mechanical problems:
Seized pistons or bearings
Hydrostatic lock from liquid in cylinders
Incorrect ignition or valve timing
Seized alternator or other belt-driven device

24. Determine tests by the likelihood of the fault.
Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (4 of 7)
Determine tests by the likelihood of the fault.
Example: If vehicle in a parking lot, better chance fault is electrical
Ease of conducting test/visual
Example: Easier to perform starter draw test than inspect main bearings

25. Measure starter motor current draw first.
Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (5 of 7)
Measure starter motor current draw first.
Slow crank with low draw—high resistance in main starter circuit or the starter
Slow crank with high draw—fault in the starter or engine mechanical fault

26. If no contamination, turn engine over to check if it is tight.
Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (6 of 7)
If mechanical:
Check oil and coolant for contamination.
If coolant and oil mixed, check head gasket or cracked head/block.
If no contamination, turn engine over to check if it is tight.

27. If still hard to turn over:
Engine Starting Systems—Differentiating Between Electrical and Mechanical Problems (7 of 7)
If hard to turn, remove accessory drive belt and spin each accessory before trying to turn engine over again.
If still hard to turn over:
Disassemble components to check them individually.

28. Summary
Testing starter motor current draw is a good indicator of overall starter motor performance.
Amperage draw can help to differentiate mechanical from electrical failure.
Voltage drop is key test for isolating electrical faults.

29. Credits
Unless otherwise indicated, all photographs and illustrations are under copyright of Jones & Bartlett Learning.