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I am working on a 2007 jeep compass (2.4) for a friend. I accidentally left the key on overnight and ran the battery down. I connected my charger and recharged the battery. When I started the vehicle, I got a check engine light, a throttle (lightning bolt) light, and a traction control light. My code reader came up with P2004, a stuck intake manifold runner), a code about steering angle, and an ABS code C121C. The engine is in limp home mode and will not reset. I reset all the error codes, and calibrated the steering angle by turning the wheel left then right to the stops per the repair manual. I removed and checked the intake manifold runner sensor, it was not stuck, and re-installed it. I still get the P2004 error and the C121C error, the vehicle is in limp home mode, and the brake pedal is rock hard, but will barely slow the vehicle. I cannot press hard enough to slide the tires on a dirt road. The engine surges from about 1000 RPM to about 2000 RPM when idling.
Is this something that can be reset using a better code reader? The C121C code seems to indicate replacing either the PCM or the ABS module, both costing over $500 each! Did running the battery down damage all these components? Any ideas would be appreciated.
Bob
 

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I'm no mechanic, but I suspect the vehicle's computer got confused by the draining battery. That you suddenly have all these problem is statistically improbable. More likely, while the battery appeared 'dead' it may have been still feeding weak current to the computer and that will mess it up.

First, I presume you replaced the battery? If its very old at all a significant drain becomes a terminal illness (pardon the pun). Even if it takes a charge, its days are probably numbered and I wouldn't trust it.

Second, presuming you've got a good battery, I'd try the Poor Man's Reset: disconnect the battery for half an hour -- that should allow enough time for the computer to clear its head and reset itself. After you reconnect, it may take a few drive cycles for the CEL to go away, or maybe not.

Maybe that will work for you. I hope so. Please report back.
 
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