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Troubleshooting Jeep Starter Troubles

Posted in How To: Electrical on July 18, 2018
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You turn the key on your Jeep and are greeted with a clicking sound, or maybe only silence. Whether you’re running late for work or headed out for weekend wheeling, that’s a situation that can ruin your day. It could be a bad battery, failing starter, or some other component in the electrical chain that comprises the starting system.

The starter typically consists of two main components: the motor itself and a solenoid used to switch positive battery voltage to a motor terminal. The motor has a small, toothed gear that meshes with a large ring gear on the outside diameter of the engine flywheel (manual transmission) or flexplate (automatic transmission). The large difference in the two gear sizes allows the electric motor to fully turn the engine enough to start it once initial combustion commences. The starter motor can draw several hundred amps of electrical current during this operation, and it relies on the integrity of the solenoid contacts to deliver that heavy current flow. If this flow is diminished anywhere along the path, insufficient current will make it to the starter motor.

When turning the ignition key results in the starter motor not turning, this is referred to as a “no crank” issue. A “no start” issue occurs when the starter spins the engine at normal speed but the engine does not begin running. When faced with a no crank issue, it’s often not wise to immediately assume the starter is the cause of the problem.

First, consider the condition of your battery. Has the starter been cranking a bit slower than normal the last few times you started it? If so, that could be a clue that the battery is growing weak. A quick check of headlight brightness can give a rough idea of battery condition. If the battery seems to be ok and you get no solid clicking sound from the solenoid, then you may have a bad solenoid or the ignition feed to the solenoid is faulty. This could be due to power not getting to the ignition switch, a blown fuse somewhere, bad ignition switch, faulty underhood starter relay, faulty transmission neutral safety switch, or a problem with the wiring or connectors that make up this ignition circuit.

You can check to see if you’re getting a solid 12 volts at the “S” (solenoid) terminal when the ignition switch is applied. Or, you can simply use a length of wire to directly jump 12 volts to the terminal from the positive battery post. Because you are in fact bypassing all safety switches, please be absolutely positive the transmission is in Neutral or Park.

A typical Jeep starter, such as this one from a 4.0L engine, has a piggyback solenoid attached to it. It bolts up to the bellhousing, getting battery ground connection directly through metal contact with the engine.

When the solenoid is clicking but the motor does not spin, the problem could be failing solenoid contacts, a faulty starter motor, or a faulty positive battery cable running from the battery to the solenoid. Corroded or damaged battery connectors can cause issues, and they should be easy to diagnose. Sometimes it’s possible to run a jumper cable from the battery to the large solenoid terminal to determine whether or not the battery cable is fine. Also, ensure your battery ground cable is intact and in good condition.

Once you’ve worked through some of these troubleshooting techniques and better isolated the starter as the suspect component, then it probably makes sense to remove it and check it fully outside the Jeep. Just make note upon removal of anything problematic with the connections that may be the true failure. Non-crank troubleshooting is generally not that difficult. You just need to determine if the problem is in the ignition circuit or the high-current circuit, then find the failing piece of the electrical path.

Here is the mechanical end of the starter. The pinion gear slides outward when the starter is actuated and meshes with the flywheel or flexplate ring gear.
The solenoid behaves like a high-current relay to switch battery voltage to the starter motor via the ignition switch. Here you can see the high-current terminals where the positive battery cable connects and where the voltage output is applied to the starter motor. When 12 volts are applied to the “S” terminal, the solenoid is energized.
Some newer starters, such as this one from a JK Wrangler, use a spade connector instead of a stud for the ignition connection. If you’re in the field and a quick check of connectors does not reveal a problem, a few taps (and we mean taps—no need to hit it so hard you break something) on the side of the starter motor with a hammer may shock intermittent solenoid contacts into working a bit longer.
Here you can see the solenoid removed from the JK starter motor. When voltage is applied to the solenoid windings, the plunger moves; this causes the electrical contact inside the solenoid to move and touch the copper contact shown here exposed on the side of the motor. The contacts tend to wear out slowly over time due to arcing whenever the solenoid is energized.
At the same time the solenoid closes the electrical contacts, the plunger also allows the starter motor gear to move outward to engage with the teeth on the flywheel or flexplate to spin the engine.
Starters are usually quite reliable in the long run unless they’re heavily abused from hard cranking duty or subjected to submersion too often. Sometimes it’s obvious when there’s corrosion near the battery terminals on a liquid lead-acid battery. However, corrosion can also lie hidden inside connectors or cables, reducing electrical continuity where it is not readily apparent. This one fooled the owner into mistakenly replacing what he thought was a bad starter.
Some Jeeps may have the solenoid mounted remotely from the starter motor, often on an inner fender panel. This type also has the same electrical function as one mounted on the motor—to switch the high-current flow to the motor. Sometimes remote solenoids are used on engine conversions where excessive engine heat can disrupt solenoid function on the side of a hot engine block.

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