Help with diagnostics would be great.

car is a 2006.5 xA, automatic trans w/ 55000 miles

symptoms are :
loss of MPG
loss of ~1/2 a volt in the electrics
possible slight increase of vibration when stopped & in gear
one time, when the car was still cold after startup, I got to the first stopsign in front of my house and the 'o/d off' trans override light came on (on it's own)

no MIL or CEL thrown

 

Have you done any electrical work to the cars (h.i.d., led bulb swap, etc.)?

 

nope

I do have an amplifier installed that draws a decent amount of juice. Also have a scan guage 2 and monitor the voltage realtime.

 

A friend lost some mpg due to changing out her plugs. She have an 05. Did h.i.d. on mine (05 also) and my tech does read right sometime but drive normal. Change out to some better quality ballast and issue stop.

 

Its' hard to diagnosis by the info/history that you are giving, all we can do is guess as there could be many variables

Are u sure you did not hit your OD in error LOL as it only happen 1x

Loss of voltage could be your amp/radio/headlights etc. when all on drawing more amperage than your stock 80 amp alternator is putting out.

Loss of MPG/vibration:
are your tires properly inflated,
Did you try fuel injection cleaner? thru the gas tank or engine
OEM spark plug change to be done every 30K

Coil On Plugs don't have a maintenance interval. Unless there is a problem - cracked insulation, rubber deteriorated, missfire - they should last the life of the vehicle. U can do a coil plug test on the car or a bench test
http://autorepair.about.com/od/troub...est-manual.htm

Have u ever looked at the PCV valve? If the PCV valve is clogged, your car might spit and sputter or even stall while driving.

 

OP any update on the suggestions?

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battery had a bad cell

case closed

 

Thanks for update. That's alot for a battery but good to know

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