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2003 Deville base
03 Deville
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15 Posts
Discussion Starter #1
Can a weakening battery cause my tranny to act funny? It seems to shift to a higher gear a little early sometimes and downshifts and upshifts a little hard at low speed. I replaced the engine/trans mount a few weeks ago, and everything is tight. No codes in DIC. Also my "lights on" indicator on the dash randomly comes on. I suspect my battery will need to be replaced soon as it is several years old. My headlights dim for a second when the AC compressor kicks in.
 

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2004 Deville
2004 Deville, Silver, Gone, but not forgotten, 1972 Eldorado, 1974 eldorado, 1975 CDV
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619 Posts
Check your tranny fluid level, with engine running and on level ground. The "Lights On" indicator i believe is controlled by the dash integration module which is built into the hvac controls, I'm having the same problem with my 04. At first i thought the bulb was out but it came on for a few minutes the other night. I plan on replacing the hvac panel but i need to pay down some other bills first
 

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Super Moderator SEMPER PARATUS
2003 DeVille Base
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4,507 Posts
Can a weakening battery cause my tranny to act funny? It seems to shift to a higher gear a little early sometimes and downshifts and upshifts a little hard at low speed. I replaced the engine/trans mount a few weeks ago, and everything is tight. No codes in DIC. Also my "lights on" indicator on the dash randomly comes on. I suspect my battery will need to be replaced soon as it is several years old. My headlights dim for a second when the AC compressor kicks in.
by "no codes in the DIC" do you mean you used the built in scanner to pull codes? Only P codes will set the SES light, but even with no SES light there could still be pertinent codes stored
 

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2003 Deville base
03 Deville
Joined
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15 Posts
Discussion Starter #4
Pulled all codes stored in the on board DTC. I also used my obd2 scan tool before I cleared all codes. Only had a few codes stored in history related to secondary air injection and door module (which have been replaced or repaired). The fluid level is spot on and the fluid life is at 100% according to the dic. The tranny was serviced 3yrs ago. Just wondering if maybe a shift module or sensor may not function properly if the charging system or old battery wasn't putting out consistently under a load. It's sporadic, not a chronic occurrence, but often enough to get my attention.
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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67,211 Posts
There have been instances of sticky/faulty 1>2 and 2>3 shift solenoids and/or a failing IMS (Internal Mode Switch). There's an updated shift solenoid kit with extra solenoid bracing.

4T80E solenoids and sensors.gif
 

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2003 Deville base
03 Deville
Joined
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15 Posts
Discussion Starter #6
Would these solenoids eventually trigger a code? Doesn't look like they would be too hard to get to.
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,319 Posts
Yes, they are monitored and should trigger a code.
 
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