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Old 09-14-2016, 05:28 AM
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Angry Sentry Key Immobiliser Light - HELP!

Having a problem with Jeep and wondered if you could give it some thought:

6AM Monday when i went to start my 2003 Grand Cherokee 4.7 the Sentry Key Immobiliser System Indicator light came on and car would not start. AA came and tried a few things but no luck. My spare key was at office and we agreed best to try that before towing to garage as that would tell whether key or car unit was the issue. Spare key tried yesterday and initially same issue. However after leaving key in car with ignition on for an hour the car seemed to recognise the key again and the car started!
Today the spare key initially gets the Sentry Key light and Malfunction light and the main key managed to start it. But not consistent and warning lights still on. Tried then with spare key works and all seems fine with no warning lights?! And finally it won't start with either key again
AA cleared all fault codes (OD26; 0210,0311,0811) most refer to communication with engine control. Today my local garage plugged in and only found P1687 - No Mech Instrument cluster BUS Message received.

I have also had "Check Gauges" fault intermittently coming on lately and even if it works next time I try, I fear an electrical fault that will recur and leave me stranded somewhere

Any ideas welcomed

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Old 09-14-2016, 08:52 PM
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Re: Sentry Key Immobiliser Light - HELP!

Do you remember if the fuel level and battery voltage where reading normal, or maybe just stayed at 0?
A shorted crank sensor can bring down the PCI data bus. The engine will then not start and the SKIM light stays on. Battery voltage and fuel level, which both come from the PCM via the PCI data bus, will stay at 0. If the problem is SKIM related, then the engine should start normally, but shut down after some seconds.
That letting the ignition in on for an hour did solve the problem (temporarely), could also point to the dreaded PCI bus problem. Most of the components are connected to the PCI bus and one faulty component can bring down the bus. There are several cases known of water ingress in connector C200 in the passengers side footwell area, where corrosion and moisture caused the bus to short out (or to bring the bus voltage up too much, by shorting to a power wire).
You can measure the bus voltage at the diagnostic connector pin 2 (the connector used to connect the OBDII reader). Normal bus voltage will be around the 2V, while it goes up and down a bit. When over 7V, then the bus is shorted to a voltage source. When at 0V, its shorted to ground.

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