Q: Jeep won't start. One click when key is turned.

Confirm that the engine immobilizer system (security system) is not activated thus preventing the car from starting. If the immobilizer system is on, you may see a security warning light. To temporarily override the immobilizer system, see these instructions. If there is no starter motor operation at all, that is if there is no starter operation with the key held in the "start" position, the procedure is to test for power to the starter motor. If there is no power, then the electrical circuit supplying the motor has a fault. That circuit begins at the battery and includes grounds, wiring (some of which is very heavy cabling), fuses, relays, the ignition switch and terminations. Basically, with a fully charged battery, and with the key held in the "start" position, the starter is either getting power or it isn’t. With the key in the "start" position, if the starter motor is getting power but the starter doesn’t work, then the starter is condemned and replaced. Note that starters can and do sometimes develop intermittent faults due to bad spots on the armature. The bottom line is if there is battery voltage to the starter (and no excessive voltage drop) and yet the starter doesn’t work, it’s dead. If you desire that a certified mechanic resolve this, please request a no start diagnostic and the responding certified mechanic will get the problem diagnosed and repaired for you. Please let us know if you have further concerns or questions as we are always here to help you.