A slow crank can come from four places: the battery, the cables and connections, the starter, or the engine itself being hard to turn. The trick is testing in the right order so you don't throw a starter at a cable problem.
Start with the battery. If it passes a load test, then it's time for a starter current draw test.
Set up the current draw test
Disable fuel or ignition the way service information says, usually by pulling a fuse or relay, so the engine won't start. Then crank it for no more than about 15 seconds while you read current and voltage.
High current, slow crank
Current way above spec means something is making the starter work too hard. That's either the starter itself dragging, like worn bushings letting the armature rub, or the engine being hard to turn.
Try turning the engine by hand. If it turns easily, the drag is in the starter. If it's tight, the engine is binding inside, maybe from overheating damage like scuffed pistons or tight bearings.
Low current, slow crank
Current below spec with a slow crank means something is limiting it. That's resistance: bad cables, loose or corroded connections, or worn solenoid contacts.
Voltage drop testing finds it. Check the positive side and the ground side separately while cranking, and compare to service information.
Cranks fast but won't start
This one's the opposite. If the engine cranks faster than normal with an even sound and won't start, the starter isn't meeting the usual resistance. Add in no camshaft signal on the scan tool, and you're looking at a broken timing belt or chain.
No crank, no click
If nothing happens at all with a good battery, the solenoid isn't getting energized. Look at its control circuit: the fuse, the park/neutral switch, or the relay. Worn starter bushings won't cause a no-click. They cause a slow crank with high current.
Cheat sheet
- Test the battery first
- Disable fuel or ignition, crank no more than about 15 seconds
- High current + slow crank = starter drag or engine binding
- Low current + slow crank = resistance in cables or connections
- Fast, even crank with no start = check the timing belt or chain
- No crank, no click = solenoid control circuit
Common questions
What causes a slow crank with a good battery?
Bad cables or connections, a dragging starter, or an engine that's hard to turn. A current draw test tells you which way to look.
What does high starter current draw mean?
Something is making the starter work too hard, either the starter dragging or the engine binding.
Why does my engine crank fast but not start?
If the crank is fast and even with no cam signal, suspect a broken timing belt or chain.
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