After reading similar issues I changed the battery.
1. sometimes I turn the key and nothing happens. no sound, no click but car has electrical power.
2. radio and interior lights go on.
3. when car starts spoiler goes up.
4. after driving car all dash warning lights go on.
5. after parking car it’s stuck in park.
6. turn car back off and restart spoiler goes down and car will go in drive.
7. park car start 2 days later and everything is fine.
8 . Next time everything starts all over again.
9. is it possible battery has enough power to start car but not enough to run electrical system?

 

It sure wouldn't hurt to have it tested under load.

 

The power required to start the car is much greater than the power required by the rest of the electrical system.
How many miles on the car and what year?
My guess is a problem with the BCM. Get pizzaguy to comment.

 

The real issue here, is that your symptoms are a mix of a bad traction control relay and a bad engine control relay (both on the RCM) and a weak battery and/or bad battery cables or maybe an alternator that is undercharging. FACT IS: You have a fundamental issue with a lack of clean, stable battery voltage in this car or you have a really bad RCM.

A few suggestions:

1) Get one of those snazzy cigarette lighter voltmeter thingys and see what system voltage is with the engine running - anything below about 13.2 is a suspect and anything down below 12.5 or so is a problem. With engine at 2000 rpm, you better see 13.8 to 14.2 volts. You are testing the alternator doing this. Alternators are easy: They prop system voltage up when ever the engine is running, if the alternator cant do that, it's bad. Yanking the alternator and having a local shop rework it is preferred to replacing it with one from Autozone/NAPA/Etc.

2) Replace the car's battery. (If you have it "tested" and the guy tells you it's fine, please don't ask for tech advice here, I told you to replace it. You can't effectively 'test' the battery for what we are chasing - do not expect the 'tech' to understand things like capacitive reactance or noise immunity.) While you are at it, make damn sure the battery terminals are clean and tight. If the cables look like hell, get them replaced, PERIOD. Don't avoid doing this because "its too hard" or "the shop says they are OK".

3) Yank the RCM and send it to DJ. (Do this even if the above fixes the car, our RCMs are known failure items and you should have the RCM reworked at least once in the car's lifetime. DJ is one of few members capable of doing this effectively.)

 

Thanks for the detailed information. I changed the battery and it didn’t solve it. Changed RCM and it solved problems.
Unfortunately there are 2 other issues:
Low Tire Pressure light flashing. Batteries are probably dead. Don’t want to spend the money to replace and recalibrate them. Can it be disconnected without disturbing something else and causing another problem?
Also air bag light on. Don’t want to have this diagnosed and traced down at a dealer either. Any suggestions?
I just want to sell the car but can’t with these lights on.
This 2008 Roadster is clean,runs great and only has 20,000 miles on it. I have too many cars and something has to go. I’m into higher horsepower Challengers and Chargers . Any help here is very much appreciated.

 

Hello Pizza Guy,
Yanking the alternator and having a local shop rework it is preferred to replacing it with one from Autozone/NAPA/Etc.

I have searched the forum and can not find a reference to this before except for the high cost of buying an alternator and/or connections not matching up.
Any other reason why rework is better than replacement?
Jim

 

Regarding the tire pressure monitor light flashing.
This has been well documented on this forum so please search it.
Power is easily disconnected so light goes out. Then get an aftermarket system that is less than $100 and gives way more information. (and does not require a sensor inside of the tire).
Jim

 

where r u & what do u want for the car?

 

I’m in Palm Bay Florida. Looking to get $25,000 for the car.

 

thanks,, I have a mech that comes here from miami, he could fix the air bag and the air ,if u r interested let me know. thanks jim