How to diagnose and fix a starter
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 wise not 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.
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.