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need help with electrical problems

2129 Views 11 Replies 5 Participants Last post by  s0v3r1gn
I've been having problems with the electrical system ever since my battery decided to throw up all over the hvac and shorted out the ecbm. A couple months ago the car started to die after 2-3days of sitting, I took it in and they went through the entire electrical system 5 times and they couldn't find out what was causing the problem. They just replaced my optima battery for me and everything was fine until last week. I came out again and the car was dead after sitting for 3days. I took it in and I had a weak alternator that wasn't producing the correct voltage, not charging the battery well. Well after that got fixed the car sat for 2 days and I tried to start it but it wouldn't turn over. I still had the lights and what not but it wouldn't turn over. I noticed the battery voltage was about 13.3 V once I got it jumped and it took 10-15 min to get up to 13.9 V. I drove up to dallas and it seemed ok. Today same thing, i'm guess that's to charge the battery? Anyways, i didn't get any codes but i'll get them tomorrow and post anything i get. Any ideas on whats going on, because I have no idea now :thud:
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I believe I got the same set of codes after disconnecting and replacing my battery for old age. Did they get checked and cleared after the battery replacement ?
I believe there's a starter to frame ground point on the frame directly UNDER the battery. To check it, the battery has to be removed. It could have been doused in electolyte and now is corroded to the point its no longer grounding the starter. That would leave the lights and everything you mentioned operational but give you the no start.
There will be some draw for keep alive like radio, clock and such but that should be on the order of milli-volts. Have you tried doing a static/dynamic voltage check with a multi-meter AT the battery terminals. Everything off should give you @12.6VDC for a fully charged battery. Running, with the alternator actually output charging the battery you should see something above that static number but certainly NOT ABOVE @ 14.6 VDC. I understand the PCM controls the alternator output but the charging system acts like a trickle charger to replace whatever was pulled off the battery for other things. The overnite unseen killer of batteries can be a shorted diode in the alternator as the diode no longer acts as a check valve to control output but becomes a conductor when shorted. This is usually a result of a "jump start". With no control device between the battery and the diode, current flows and acts much like a courtesy lite left on, the slow draw can take the battery down below 10 volts and it may never recover properly. If you have had the alternator replaced, it had to be replaced with EXACTLY the correct alternator for the VIN. The PCM is looking for the right numbers and will throw "charge faults". Each year there were changes made that the PCM has been programmed to see.

Have you done any SEARCHES on other VETTE Forums looking for similar problems ? Here's an example-

Hey guys, just a question, I went to start my 02 Z up today and it wouldn't start, the speedo/tac/lights all went throught the testing/startup process and then I heard a humming noise but the engine didn't start. Any ideas what could be wrong?

You either have a bad Theft Deterrent Relay (TDR),, bad solenoid,,, or a defective starter. I would also check to see if the main power wires and ground wires off the battery to the starter/engine are in good condition, clean and tight.

Mine does the same thing. If I continue to attempt to start the car, it will start. Havnt had time to sit down and mess with it. Guess, I get stranded one day and have to fix it.

I teach AIRCRAFT ELECTRICAL SYSTEMS and the VETTE is a challenge in the spark department. I'm just a new owner, but I'll cut my arm off before I'll take it to the "Stealer" to get it worked on. I got the 3 vol service manual set and I'm looking for anything I think may help you. I just checked my car - 12.78 VDC static, 14.28 VDC dynamic
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Read this post from Corvette forum!

You have the wrong alternator in your car....If you had a credible dealer, they would have told you this.... Problem is they dont realize that your new alternator is not communicating with your old PCM... I'm guessing that you now have an alternator that puts out more than 110 amps.. You PCM is expecting to see a full duty charge of 110 amps>

The alternator is very specific to the PCM...
GM's upgraded alternator is a poor fix... while it is functioning fine... the PCM thinks it isnt...

The only way to Fix this problem for sure is to have the original alternator rebuilt..But it just cant be a 110 amp GM alternator it has to have the specific part number GM 10246634 because of the specific switching found in this alternator, that talks with the PCM
Good Luck and I apologize for the poor service found at your dealership.
Bill aka ET

I've posted this many times, and you may find it of some insight.

The PCM monitors the alternator through the red and grey wires The L-terminal circuit from the generator is a discrete circuit (a discrete circuit has no splices and only one source and destination) into the PCM. The PCM applies ignition voltage to the generator L-terminal circuit. A small amount of current flows from this circuit through the generator windings to ground to create a magnetic field which starts the generator process. When the generator is at operating speed and producing voltage, a solid state switch for the L-terminal circuit in the generator opens and the PCM detects that the initial startup current flow has stopped.

The PCM expects to detect low voltage on the L-terminal circuit prior to the generator rotating at operating speed and conversely expects the circuit to be at ignition voltage potential when the generator is operational. When the PCM detects a fault (circuit shorted to ground, or circuit shorted to voltage), the Driver Information Center will display Charging System Fault.

The generator has an input to the PCM called the F Terminal to indicate the percentage of total capacity that the generator is producing. This signal is detected by the PCM as a duty cycle from the generator and displayed on the scan tool as a percentage. The PCM can monitor the generators output under all conditions to determine if it is functioning normally.

When there is low demand from the electrical system on the generator, a low duty cycle percentage will be displayed. As more accessory load is placed on the generator, the duty cycle output detected by the PCM will approach 100 percent. A normally functioning generating system will never reach 100 percent as indicated on the scan tool.

The L and F terminals are the red and grey

I hope this helps...
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