Failure to start falls into two categories:
1) The engine will not turn over – the starter motor will not run or,
2) The engine turns over but will not fire and run.
This article will address the first cause. If your engine turns over but will not fire see my other article.
Start by checking the battery voltage. Most Jeeps have a voltage meter on the dash. If the voltage is low – below 10 volts, check the following:
- First, check to see if there is a cause for the battery to be discharged. Were the lights left on? Doors left open or other power-draining accessories left on? If so, turn off the drain and use jumper cables to start using a charged battery from a different vehicle.
- If there has been no excess power drain, check the condition of the battery cables. Remove the cables from the battery posts and clean the contacts. Also, check the connection of the ground cable to the vehicle body.
- If the battery cables are clean and making good contact and the voltage is still low, verify that the alternator is functioning properly.
- If the battery continues to fail to start your Jeep, replace the battery.
If the battery voltage is normal but the engine still will not turn over, the most common cause is one of the safety interlocks. On an automatic transmission, there is a Neutral Safety Switch (NSS) that only allows the engine to start in neutral or park.
The contacts in the NSS can corrode and cause the switch to malfunction. Move the shifter back and forth while turning the key to start. Often the motion will cross a spot on the switch that still works. The NSS can be disassembled and cleaned or simply replaced with a new unit.
If the NSS is working properly but the starter still will not turn, you may have a defective starter or starter solenoid. The starter and solenoid are replaced as a unit on the XJ Cherokees.
However, before buying a replacement starter, check the wiring connection on the starter and the trigger wire to the solenoid. Often these connections can become loose or dirty due to the rigors of off-road driving. Some people have reported that starters can be disassembled and cleaned to correct problems but I have not tried this procedure.