Diagnose a no start Jeep condition
Why your Jeep won’t start
If you own a late model Jeep with a no start Jeep problem, this article may help. This help article pertains to 2010 thru 2012 Jeep Avenger, Jeep Compass and Jeep Patriot, although the trouble shooting applies to many other Jeep and Chrysler products since they all use similar wiring
The symptoms appear as a crank, no start where the starter engages and turns the engine but it will not fire up.
How the Jeep system works
The ignition switch on late model cars doesn’t actually switch power to the starter, ignition or fuel system. The switch acts only as a signal to the PCM/body control module. When you turn the key, the PCM/BCM anti-theft system determines whether you’re using the proper key. If so, the PCM provides ground to the auto shutdown relay (ASD), also called the MAIN relay which then operates to provide power to the totally integrated power module (TIPM) which provides power to the fuel injectors and ignition coils. If there’s an issue with the ASD relay or the wiring to the ASD relay, you’ll get a no start Jeep condtion.
What goes wrong with Jeep starting system?
In their wisdom, Chrysler placed the ASD relay below the battery and behind the driver’s side headlight. Over time, corrosion can rot out the wires to the ASD relay socket.
Diagnose no start Jeep
Here’s where to start your diagnosis. First, scan for trouble codes. If the ASD relay or wiring are bad, you may get a P0685-ASD/MAIN CONTROL CIRCUIT or P0688-ASD RELAY CONTROL SENSE trouble code.
Check fuses first:
The battery provide power to the TIPM. Fuse 33 10A in the TIPM provides power to one side of the ASD relay control coil on the red/light blue wire. Fuse #18 40A provides power to the ASD relay contacts on the red/yellow wire.
Once the key passes the anti-theft test, the PCM provides ground to the control coil side of the ASD relay on the brown white wire. Once the ASD relay receives ground from the PCM, the contacts close and the relay sends power back to the TIPM on the brown/white wire. The TIPM routes that power to Fuse 32 30A, Fuse 26 15A and Fuse 23 15A.
Fuse 32 sends power back to the PCM so the PCM can monitor the status of the ASD.
Fuse 26 provides power to the fuel injector and Fuse 23 provides power to the ignition system
So check all those fuses
Then check ASD relay wiring
Shops have found severe corrosion on the ASD relay socket terminals that has resulted in corrosion all the way down some wires. Shops have also found broken wires under the ASD main relay box as far as 3” away from the box. How to test Jeep main relay
Remove the main relay from the socket. Check for corrosion. If good, use a digital voltmeter to test for power in the main relay socket. With the key turned to the RUN position, check for battery power on two terminals and ground on one terminal in the socket. If you don’t see battery voltage on two terminals and the fuses listed above test good, check the red/light blue wiring from the TIPM to the main relay box. If you don’t see ground from the PCM in the socket, check for ground on the brown/white wire coming from the PCM. If you still don’t see ground and you don’t have an anti-theft issue, you may have a bad ignition switch. Grab a wiring diagram and specs and test for proper IGNITION switch operation.
If you see those voltages and ground, put the relay back in the socket and test for battery voltage on the red/yellow wire. If you don’t see battery voltage, chances are the relay is bad.
©, 2017 Rick MuscoplatPosted on by Rick Muscoplat