My girlfriend just purchased an 08 Chevy Cobalt for $2500. The guy she bought it from said that it just had a bad battery, so I jumped it and it started right up. I drove it around and everything was great, so I couldnt pass up on the price. I took the battery to have it tested and charged and everything was fine with the battery but the car still wont start. I assume it has to be a bad starter? Every time i jump the car it starts up fine. I can even sometimes restart the car without a jump after it runs a while. The guy tried unsuccessfully to put a remote starter on the car and I didnt know if that could also be the problem? Has 110,000 miles on it. Also the engine doesn't even try to to turn over. All of the lights, horn and radio will turn on when the car isn't running. .
Is there a warning light , padlock an car symbol lit when it won't start ? I assume it has to be a bad starter? Every time i jump the car it starts up fine.??? It wouldn't be a starter then ! Have the charging system check out . Have a voltage drop test on the starter circuit done . Test from the starter relay . check out videos on youtube , but don't assume anything . Test , Test Test .
https://www.youtube.com/watch?v=WMXENKujYtc&t=6s
Starter Voltage Drop
VEHICLE RELAYS Testing from the relay base
Plus you need to know how the starter system works for the vehicle your trying to diagnose . I 'am a GM tech , Chevy , Cadillac , buick , GMC. Have access to GM factory repair info. Been to a lot of GM training school's . The computers on this vehicle have a lot to do with the starting of the vehicle ,PCM - engine computer , the ignition switch is a low voltage input to the BCM - body control module , which will send a message over the GMLAN serial data communication network to the PCM to energize the starter relay or crank relay .The PCM also has to see a voltage input coming from the transmission range selector switch , showing it's in park or neutral , has to have correct fuel enable password from the theft module etc...
Also it take's is a little corrosion , lose connetion , lower then normal circuit voltage for problem to happen .
Factory service repair manual discription
Moving the ignition switch to the start position signals the body control module (BCM) through discrete inputs from the ignition transducer that engine crank has been requested. The BCM verifies that theft is not active and sends a serial data message to the engine control module (ECM) requesting engine start. The ECM receives a ground signal from the park/neutral position (PNP) switch or a signal from the clutch pedal position sensor notifying that it is safe to start the engine. Ground G105 supplies ground for the CRNK relay coil. The starter relay coil control circuit is then supplied voltage by the ECM closing the switch in the starter relay suppling 12 volts from the CRNK fuse to terminal A of the starter. Ground is supplied to the starter solenoid through the engine block.
The first step in diagnosing a problem like this , hooking up factory scan tool , checking for DTC'S - diagnostic trouble code's , checking inputs to control modules that are in charge of starting the vehicle .
Testing an knowledge is the way to a fix , an testing cost $$$$$
SOURCE: Car battery won't stay charged.
jumped battery started next day attempted to start and was dead i swapped out a battery no good then i swapped out the terminals to the battery and it started right up
SOURCE: 1994 Toyota Tercel Starter Problems
sounds to me that you have an igniton problem not a starter problem and or if you have or had an alarm system could be cause if u do give me feedback and i will explain but seems that your starter is fine from what u say but if you think in terms of the elemts to start a vehicle batery gives pwoer to ignition which sends to starter which gives spark etc i would check you ignition system something is causeing a short and not alowing starter to function
SOURCE: Theft lock 2005 Cobalt
If the BCM has been replaced, the BCM has to be reprogrammed by a dealer as it control many car functions.
SOURCE: cadillac 2004 cts, wont start
i had a 2003 ctc that did the same thing, it wouldn't start or would make a clicking sound and about 1 mth after the problem started aND mechanics could not find a problem my car caught on fire and burned completely from something under the right side of the hood. i had just parked the car and got out, it happened really fast. the fire chief said the cause was unknown????
now i have a 2004 cts and i'm having the same problem!!!!!!!!!!!!!!! has anyone else had this happen???? please be cautious if your cts is doing this, during the fire my doors locked and had to be pried into by fire chief.
SOURCE: 87 f250 drained brand new battery
I would first have the alternator checked by an auto electrician to ensure it is working correctly and is providing the correct volume of current. It may be faulty and when driving you will be drawing battery power instead of power from the alternator to run the electrics. This will drain the battery.
Alternators do not last forever and if you are still running the original unit it is likely to be on it's last legs and you will need a replacement unit.
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