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ttiger79, ASE Certified Technician
Category: Jeep
Satisfied Customers: 1257
Experience:  Advanced level L1 ASE master certified technician
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My jeep wont start. It will turn over, but wont fire. The

Customer Question

My jeep won't start. It will turn over, but won't fire. The gauges and lights all come on, but show nothing. Shows I'm on empty, which I know there is a half tank. It also has a brand new battery. I had no warning. Yesterday, it ran perfect. The guys at the Jeep dealership won't answer me, just keep telling me to bring it in.
Submitted: 8 years ago.
Category: Jeep
Expert:  brownjeff replied 8 years ago.
What have you checked so far? Does it have fuel? Spark? Compression? etc.
Customer: replied 8 years ago.
It has fuel. It has spark. I'm not sure about compression. Not sure what that means.
Expert:  brownjeff replied 8 years ago.
You have two more things to check. The vehicle needs compression,spark, and fuel at the right time to run. So you need to check the timing as well as the compression. Compression is when the fuel is compressed by the piston the valves are closed and then the spark will ignite it.
Customer: replied 8 years ago.

The transponder in the key is not being recognized by the vehicle. My husband just told me that it doesn't have any of those things because the vehicle is not recognizing that there is a key in the ignition. When we turn the key, the key light comes on (and stays on) and the car sounds like it is cranking and wants to start, but it won't. My husband thinks it has to do something with the security system.

Expert:  brownjeff replied 8 years ago.
If the security system failed the vehicle would start and run for a couple seconds then shut off. Does the vehicle start at all?
Customer: replied 8 years ago.
No. It just keeps trying to turn over, but never starts.
Expert:  brownjeff replied 8 years ago.
Then if the vehicle has spark and fuel I would check compression and timing next. The security system will not effect theses two items.
Customer: replied 8 years ago.
Would that keep the key light gauge on? The circle with the slash over the key won't go off. That's why we think it has something to do with the ignition.
Expert:  brownjeff replied 8 years ago.
I will opt out and see if someone els can help you.
Customer: replied 8 years ago.
Does anyone have an Idea? According to what we've just found online, is that it would be an electrical problem.
Expert:  ttiger79 replied 8 years ago.
You are correct with your research. The problem that you are having is with the SKIS antitheft system. Unfortunately, there's nothing that you (and almost all shops) can do about this. You will need to have the truck towed to the dealership for this problem. Here's a basic description of the system:

Each ignition key used in the Sentry Key Immobilizer System (SKIS) has an integral transponder chip. Ignition keys with this feature can be readily identified by a gray rubber cap molded onto the head of the key, while conventional ignition keys have a black molded rubber cap. The transponder chip is concealed beneath the molded rubber cap, where it is molded into the head of the metal key. Each new Sentry Key has a unique transponder identification code permanently programmed into it by the manufacturer. The Sentry Key transponder if faulty or damaged, must be replaced.

When the ignition switch is turned to the ON position, the Sentry Key Immobilizer Module (SKIM) communicates through its antenna with the Sentry Key transponder using a Radio Frequency (RF) signal. The SKIM then waits for a RF response from the transponder through the same antenna. The Sentry Key transponder chip is within the range of the SKIM transceiver antenna ring when it is inserted into the ignition lock cylinder. The SKIM determines whether a valid key is present in the ignition lock cylinder based upon the response from the transponder. If a valid key is detected, that fact is communicated by the SKIM to the Powertrain Control Module (PCM) over the Programmable Communications Interface (PCI) data bus, and the PCM allows the engine to continue running. If the PCM receives an invalid key message, or receives no message from the SKIM over the PCI data bus, the engine will be disabled after about two seconds of operation. The ElectroMechanical Instrument Cluster (EMIC) will also respond to the invalid key message on the PCI data bus by flashing the SKIS indicator ON and OFF.

Each Sentry Key has a unique transponder identification code permanently programmed into it by the manufacturer. Likewise, the SKIM has a unique Secret Key code programmed into it by the manufacturer. When a Sentry Key is programmed into the memory of the SKIM, the SKIM stores the transponder identification code from the Sentry Key, and the Sentry Key learns the Secret Key code from the SKIM. Once the Sentry Key learns the Secret Key code of the SKIM, it is permanently stored in the memory of the transponder. Therefore, once a Sentry Key has been programmed to a particular vehicle, it cannot be used on any other vehicle.

What has happened is the SKIM module isn't getting the correct signal from the key. Either you have a bad key, bad antenna ring in the column, a bad SKIM module, or bad wiring somewhere in between these components. The Jeep will start then stall a few times, then the PCM will be forced to go into "sleep" mode until the problem is fixed. This is a dealership repair only. Any component of the system will need to be programmed by the dealership scantool upon installation, and the system will need to be reset.

Let me know if you have any more questions!
Customer: replied 8 years ago.
Crank Shift Sensor? The whole anti theft thing doesn't match up to what is happening. According to what we have found, is that if the light blinks, then it is an anti theft problem. If it stays on, then it is an electrical problem. It stays on. We found info on the Sensor, and did the "test", (by unplugging it, etc.) and that seems to fit the description very well. The sensor is only $40, so we are going to try it and see what happens. I'll let you know when I find out.
Expert:  ttiger79 replied 8 years ago.
The crankshaft position sensor, when it fails, you will lose spark from the coils. If you know that you don't have spark, this is a good place to start. Keep me updated on what you find, or if you need install instructions on the crankshaft position sensor.
ttiger79, ASE Certified Technician
Category: Jeep
Satisfied Customers: 1257
Experience: Advanced level L1 ASE master certified technician
ttiger79 and 2 other Jeep Specialists are ready to help you
Customer: replied 8 years ago.
It was the crankshaft position sensor. Truck is running perfectly now. Although we figured out the problem on our own, I will go ahead and accept for taking up your time. Thanks.
Expert:  brownjeff replied 8 years ago.
Glad you got it running.

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