2000 jeep cherokee no start high voltage

start
alternators

#1

problem with my 2000 Jeep Cherokee; open door, no dome light. turn on key, nothing on dash/radio/windows whatsoever. turn key, nothing. leading you to think it’s a main fuse or relay.



connect jumper cables, dome light works. turn key, dash operates and car starts as it should. but here’s where it gets tricky; drive or fast idle vehicle for a few minutes at 2-2.5k rpm and the volt gauge will max-out at 19v along with the check gauges light illuminating. check voltage at battery and it’s showing 13.8v.



reduce rpm’s to idle (600-700rpm’ish) for a couple minutes and the volt gauge goes back to 14v and the check gauges light extinguishes. turn car off and the same thing happens; no dome light etc until you install jumper cables…



installed a battery/computer/ASD relay from a friends 99 cherokee with same results; no dome light etc…



followed chilton’s charging system troubleshooting; car off, disconnect neg lead from battery, connect test light between the cable/post, light on (short somewhere in car). disconnect alternator harness and still get light. it then tells you to remove fuses til the light goes out, removed all fuses under the hood and in the passenger kickwell, light never went out.



i ordered an alternator as soon as i installed a friends known good computer (regulator built into the computer) and it didn’t fix the problem, still waiting for it to arrive. tonight i intend to try the same light test, but disconnect the three PCM connectors, one at a time.



additional factors: the horn that used to sound when you hit the lock on the keyless entry fob hasn’t sounded in two years. just before the trouble started last weekend while my wife was getting into the car, she opened the door and just as she was stepping in all the locks cycled. i asked her what she touched and she said, ‘nothing’. then, we stopped to look at another tourist attraction and this is when the trouble started. i’ve tried to reset the antitheft by cycling the locks on both front doors and rear hatch.



btw- i’m stationed in italy and can’t just take it to the local dealer for repair. i’m used to performing my own maintenance, but this has myself and fellow aircraft techs baffled. not to mention it’s about a 2 week wait for parts to arrive and the vehicle is supposed to get on a boat to return stateside in less than a month…



any assistance you can provide is greatly appreciated.



thanks,



keith


#2

Having the voltage go up so high while the engine is reving may mean the alternator has trouble. The higher voltage may be AC and that could be why you didn’t see it with your DC meter. If you have more than .1 volts AC at any time while the engine is running the alternator is bad. The PCM controls the charging of the alternator so that is involved also.

It sounds like there is a current draw draining the battery and hopefully replacing the alternator will cure that. You stated you removed the alternator wiring and still showed a draw using the light but you need to be aware that the systems need to go into the sleep mode and current then goes down before you decide there really is a problem. This can possibly take a few minutes or sometimes more depending on the vehicle. If you repower the systems they come back out of the sleep mode and you have to wait again for the process to happen again. Normal draw should be around 35 milliamps when everything is shut down that should be.


#3

You might want to check (if your vehicle has one) the battery temperature sensor. Yes I know it sounds weird but there is a sensor under the battery in the battery tray that reads the ambient and battery temperature to tell the computer how much voltage to pump out. The colder the temp, the more voltage it lets the alternator crank out and vice-versa. If the sensor is faulty, it may be telling the alternator to charge too much. I’m not sure HOW to check the sensor, but I’m sure you could find a string somewhere that would tell you how. Good luck.