AT/Check engine light

[Newt8245]

My 2008 CX9 recently started showing the AT light on after starting and shifting into reverse. The car was then stuck in third gear. After shutting it off and strting it again everthing worked fine.Took it in to my dealer and they could not come up with anything as by now the check engine light was off. They suggested it might be the battery. Stating if it wasn't providing sufficient electrical out put this could affect the computer.I purchased a new battery and the problem disappeared for about too weeks. Once it started happening again I happened to be near an auto parts store that check codes for free. They came up with the following three codes;
1)V0100 (???)
2)V0073 (Communication with engine module failure)
3)V0101 (Communication with transmission module failure)

Anyone with any ideas on what would cause this and if it is difficult to fix?

 

[ceric]

V0100 is also a comminucation failure.
This is one from Ford. Actually, most codes are standard on OBDII. Some are specific to certain brands and models.
"I have a trouble code V0100 that reads lost contact with ECM/PCM on a 2007 Ford 500. Starter will not turn over."

You need to take it to the dealer. Before that, please measure the battery voltage with a multimeter.
The normal voltage is
1) ~11.5V when engine is off
2) 13.5-13.8V when engine is on
I really don't think it is the battery that is causing it.
My guess would be that one of the control modules is going bad.
Could be the BCM or ECU. Since the error codes are known, dealers can find out the cause
and which module to replace.

 

[Newt8245]

Thanks Ceric. Got the same response from local mechanics. We'll take it in. Hopefully it is the ECU and can be reprogrammed vs replaced. The vehicle only has 56K on it. Still love the ride!!

 

[driggy]

Just a thought. If the battery fixed it for a few weeks, maybe the alternator is getting weak.

 

[ceric]

Just a thought. If the battery fixed it for a few weeks, maybe the alternator is getting weak.

2) 13.5-13.8V when engine is on

If the voltage is lower than 13.5V when engine is on, that could mean the alternator is weak.