Jeep Grand Cherokee No-Start: Quick Diagnosis & Easy Repair

This 2011 Jeep Grand Cherokee had to be towed into the shop due to its no-crank/no-start condition. However, upon testing, the vehicle started multiple times a day for 4 days in a row. It wasn’t until we pulled it out of the shop to park it in the lot that we ran into a major problem. While backing out, the vehicle shut off on its own and refused to start back up.

Since the Jeep shut off while moving and would not crank, I was able to eliminate a crank sensor issue as the cause. Experience told me to look into the ignition system next, as that is the only system that could cause both issues. I opened the underhood fuse box to access the relays related to the ignition system. Pulling up a wiring diagram showed the starter signal to come from the Run/Crank relay.

To properly test the relay, I used a relay tester kit and a Power Probe circuit tester. With the key off, there is 12V on 3 of the 4 pins of this 4-pin relay. The 4th pin will be at ground, 0V. The pin with 0V will become energized when the ignition switch is turned to the “start” position. One of the other 3 pins will change from 12V to a ground (0V) pin at the same time. This change energizes the coil inside the relay, causing it to turn on.

On this vehicle, the 12V pin changed to 0V, so the signal to start the car was there. However, the relay did not send power down the 4th pin.…