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90 Eldo -SOLD-, 98 ETC -SOLD-, 86 XR4Ti Track Car, 07 Ranger
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963 Posts
Discussion Starter #1
Your alternator.

I say this because of the secondary effects it can have on the rest of your systems.

1) Cooling, this is critical, why would your alternator make a difference here? Because if its failing or putting out lower voltage guess what, your fans aren't spinning as fast as they should and you're not cooling your car which is very important due to the design of these cars (especially in summer).

2) Air Conditioning, weak A/C at idle is a symptom not only of potentially bad A/C related parts, but also of a weak alternator for the same reason as 1, if your fans aren't drawing enough air, your heat exchanger won't be working as well, leading to poor idle cooling performance.

3) TCC / ABS codes. You are far more likely to get these codes when idling a weak alternator and then hitting the gas. The sudden draw will drop voltages across the board and if it goes too low will set the low voltage code and disable your TCC and ABS, this is annoying in stop and go as it locks out 1st gear

4) Poor WOT performance. Weaker alternators can severely limit how hard you can push your car as the resulting voltage drop from a partially failed alternator can lead to higher rpm stumbles, cutoffs, "Service Charging System" message/codes, or worse, a lean condition due to too little power reaching the injectors.

5) Other PCM, TCC, RSS, etc codes. Looking through the FSMs, there's a boat load of low voltage codes that can be set w/o a DIC message that can actually alter the car's behavior w/o the driver knowing.

Long story short, go into your DIC and modify the checksum value to add battery voltage to the display and keep it up as in indication. The FSM says the voltage range on startup should be 14-16V, while driving 13-15V, and nothing about idle, from my experience a good alternator will put out somewhere close or around that range w/o too much dropoff. If you're seeing it drop to 10-11V at idle, go to AutoZone or the like and get a free alternator test. If it's weak or bad, REPLACE IMMEDIATLEY, you'll be glad you did...
 

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90 Eldo -SOLD-, 98 ETC -SOLD-, 86 XR4Ti Track Car, 07 Ranger
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963 Posts
Discussion Starter #4
i always thought cooling was the most important
See #1, I should have added that any electrical component of your cooling system including failing cooling fans are bad news, bad relays, and fuses, these should be inspected annually to ensure they are operating properly...
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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The most CRITICAL component on (in) your Cadillac is YOU along with a thorough understanding of the mechanical, electrical, and electronic principles involved in keeping the thing running properly.
 

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'98 ETC Black 90k miles
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1,061 Posts
My alternator puts out about 13.5V at idle (just checked not a minute ago) and is steady there. Sometimes after a lot of highway driving it will decrease to 13.0 or 12.5 if I pull over into a rest area and idle in a parking spot for a minute or two before shutting the motor off and exiting the car. This usually happens on colder, wetter days, and always goes right back to 13.5 after more than two minutes at idle. But it doesn't happen more than half the time. Either way, I agree that the alternator is very important, but Sub is correct that the driver/owner is the most important part. This is why we're all here - to ask questions and share experience.
 
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