Engine cranks but does not start

JONES8895

MEMBER
2012 JEEP LIBERTY
3.7L
V6
4WD
AUTOMATIC
200,000 MILES

For months, I was having an issue with starting with my car. A new starter was put in back in September. All my lights would cut on but wouldn’t start. This mechanic told me to take my negative cable off, slip it back on and it would restart the system. That worked until it didn’t work anymore, which also caused the cable to become way too loose. A month ago, I started having jumpstart problems, where I would drive my car just fine, I would go out there next day (sometimes it would be fine, but I thought it had something to do with the cold weather) or 2-3 days after to start it and the battery would be completely drained. I found out the negative cable was so loose; it wasn’t keeping a charge to the battery, so I thought. So, because of having to jumpstart it so much or because of the negative cable, it caused the battery to go bad. Yesterday, I put a brand-new battery in. Now, my exterior and interior lights cut on and the car dings, but it won’t start up. There is also a rebuilt alternator in the car. That was put in back in I want to say March or April of last year.

6 Replies

AL514

MECHANIC
4,120 POSTS

Hello, why was your mechanic having you remove the negative cable to start it? Did he give you a reason for this? Thats not a normal condition by any means. Actually, taking the negative cable off and on every day like that can cause serious problems. Vehicles today are all computer controlled and removing the negative cable everyday can cause issues with the engine computers' memory. It also causes a current surge on any power feeds that are constant and there to keep the computer's memory alive. Every time you hook up a battery cable that has a connection to a computer that's a direct feed (meaning it's not controlled by the ignition switch) and the computer in the vehicle is cold, there's something called Inrush Current. It's quite high current flow will eventually cause damage to electronic components.
These Jeeps have a Totally Integrated Power Module, and these modules have part of the vehicles computer network that run through them, and they have a lot of problems to begin with.
Since your vehicle is in a no start situation now, it will need to be checked for Ignition Spark and Fuel pressure to begin with.
It should be scanned for diagnostic trouble codes too. But I suggest bringing it to a different shop this time. Someone who knows how to properly diagnose vehicles. You don't want to end up with this same situation again. I know it's very frustrating.
One thing to check, does the Check Engine light come on when you turn the key to the On position, or cranking the engine over? It should last for about 2-3 seconds, which means the Engine computer is at least powering up. But I'm guessing you have some other larger issues going on here.
The Vehicle does crank over, correct? Just won't start.

https://www.2carpros.com/articles/how-to-test-an-ignition-system

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

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Thursday, March 3rd, 2022 AT 9:49 PM

AL514

MECHANIC
4,120 POSTS

Yeah, the starting system in this vehicle has a separate wireless Ignition node or module. The Ignition switch sends a voltage signal to this module and the module communicates with the Totally Integrated Power Module (TIPM) by means of the CAN bus network. The TIPM contains the Starter Relay. I will put the wiring diagrams below so you can see how it works. But these TIP Modules have issues with corrosion from underneath. And since they have communications built into them, they cause a lot of problems.
It's not really an easy system to diagnose. We would look at the communications on an oscilloscope and check voltage signals. I can't say exactly what has failed on your vehicle.

There is a circuit board in the TIPM that controls the Starter Relay as you'll see on the wiring diagrams, there is a fuse you can check in the engine compartment on the passenger side (Fuse J17, 40Amp).
This is one of those situations where you would have to take out the Starter Relay and check the Pins that it plugs into for battery power and Ground.
If you look in the 1st diagram, to the left is the Ignition Switch and you'll see it sends a signal to the Wireless Ignition Node, that in-turn sends a signal by way of the CAN bus network to the TIPM to energize the Starter Relay. Thats what you would need to check while someone else is trying to start the engine for you.
There's a few guides below to help you if your comfortable doing this type of work. It can get somewhat complicated though if there's a problem with the Communications Network.
But I think this is a result of the bad advice that the mechanic gave you unfortunately.
If the Security System loses its memory due to the battery being unhooked so many times, it may need to be reprogrammed.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-a-car-fuse

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