Expert: Roland Finston - 1/29/2012

Question
QUESTION: I have a 1998 Chrysler Concorde 2.7L with 155K. I have owned the car for 5 years with few problems. Occasionally when I would park on a hill on a warm day, the car will run rough for a few minutes after it was started. In addition, 5K miles ago the water pump was replaced. One day while doing errands, I stopped at a store when I come back to my car 10 minutes later, the car was dead..no interior light. When you turn the key all the dash light flash on and off and you can hear a clicking from under the hood. The car will only start if jumped by another car. It will stay running about 20 minutes with a fully charged battery and then die. The ignition switch, starter, and battery have been replaced. The alternator checked out good.  My husband is starting to think it may be the PCM. Please help.

ANSWER: Hi Becky,
The fact that the alternator checked out and the battery has been replaced suggests that there is some sort of a short circuit in the electrical system that is draining the battery when it is parked as well as when you are driving it. The way to find it is to remove the -post clamp from the battery and insert an amp meter between the clamp and the battery to measure the current flowing in the system. With everything off and all doors closed it should be in the range of 25-50 milliamps, dropping to that level within 20 minutes aftershut down to allow for timing-out of several control modules. If that shows alot more current flow then you start removing fuses one at a time from the box in the engine compartment until you find the one that significantly drops the current to the desired level. Then you put it back in and do the same thing with the fuse box behind the left end-cap of the dash until you find another fuse that is supplied by the fuse in the engine box. Then let me know which fuses are involved and we can go to the items that draw on those fuses to find out why.
If the ignition off current draw is OK, then we need to do this same measurement with the engine running to see whether indeed the alternator is working and the current flow is positive.
Is the battery warning light 'on' when you are driving? What does the current flow gauge on the dash show for a reading while you are driving?
I doubt this has anything to do with the pcm which is a control module which is a solid state device which doesn't in itself use much current, rather it controls current. But seldom have I heard of it causing battery discharging due to its failure.
Roland
PS: Try turning the ignition key:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. The watch the odometer window to see if the mileage reading changes to show any 4-digit numbers preceded by a P. That would be a fault code which may in fact point directly to the source of the problem.

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QUESTION: The amperage is 5 milliamps with the engine off and waiting 20 minutes. Therefore, I have not went ahead with the removing of the fuses. What is the next step you would suggest?

Also, the car is not displaying any fault codes. The battery warning light is not on when the car is running.

Answer
Hi Becky,
It sounds like there is some sort of an intermittent short circuit, or an intermittent malconnection of the battery to the overall system. I would suggest that the next time this happens that instead of doing the jump that you verify whether or not the full measured  battery voltage is actually appearing inside the power distribution box under the hood at the large fuses. Also of course see what the battery is reading at that time in terms of voltage so as to id whether it is truly discharged. I would check the - post clamp of the battery and trace the wire connected thereto to its far end to be sure it is well connected. It could also be that you have a corroded/rotten wire on the + post clamp of the battery also. There is no evidence that there is a consistent short circuit based upon the 5 mA reading with the ignition off.
Roland