QuestionDear CAJUNSC,
This is a Chevy question, but hopefully you can help.
The battery in my son's 2000 Monte Carlo (3800 engine) went dead overnight. I suspect it has something to do with the coolant fans.
At times in the past the fans would continue to run when he shut the car off. This could be remedied by turning the key to “run” and then “off” again. Sometimes this had to be repeated two or three times to fix the problem. The dead battery problem was not happening at this time.
Night before last, the fans were “off” in the “accessory” or “run” positions, but would start running when the key was turned to the “off” position. He left the key in the “accessory” position overnight, with the radio off and nothing plugged into the cigarette lighter, etc. This is when the battery died overnight. (The battery is 2 ½ yours old.).
We recharged the battery. It drew >8 amps from the charger for 2+ hours, so I don’t think the battery is weak. There was apparently still perhaps a slight “drain” on the battery as there was a little bit of sparking when the battery cable was reconnected, even though everything was “off’ in the vehicle. (Maybe this is caused by the computer, clock, etc?....)
After the car was started, everything seemed OK when it was turned off, but perhaps this is because the engine was cold and the fans were not being called for.
This is as far as I got (had to return home 150 miles away.) Is there a relay involved in the fan circuit that can fail with these symptoms? It seems like it could be a wiring problem because the battery was drained even though the fans were not running.
Any thoughts on likely causes, or further diagnostics, would be appreciated.
AnswerHi
I have had 3 different vehicles in the last 6 months with VERY similar and or identical problems.
First lets eliminate 2 things.... the battery and the fans.
The battery will draw AVERAGE about 200-500 milliamps when FIRST connected, this is "waking up" all the modules, and them sharing power mode communications and other generic data. After ABOUT a min., the draw should slack off to USUALLY between 15 and 30 milliamps.You can test this preforming a current draw test with a Digital voltmeter in the amp mode. This would be the ONLY way to determine if there is an excessive current draw. IF there would happen to be, you would then remove fuses one at a time until the draw ceases. Then that circuit should be checked.
OK The fans only do what current is given to them. If current becomes avalible, they turn on.
I do not want you to spend needless $$$$$ parts... so IS the Service Engine Soon light on???
IF so, and IF it is code P0128 your thermostat is the problem, and FOR SURE the problem with the fans.
That was one of vehicles
The next was the ignition electrical switch. This problem also OCCASIONALLY would make the car not start and "click" from under the passanger side (glove box) area. I would also suspect this IF you do not have a Service engine soon light on.
The last was the BCM and PCM (Body Control Module and Powertrain Control Module) Theis particular vehicle had various "U" codes (communication codes) stored in the various modules and found the BCM telling the PCM to keep the fans on due to the Air conditioner being "on" (The module thought the a/c was on, but in reality it was not, but it requested fan at all times) The PCM I think had grounded out internally and in turn grounded out the BCM.
So there is my 3 vehicles that kicked my butt. Each was VERY time consuming hair pulling vehicles.
I will tell you, IF you have access to a scan tool, I would HIGHLY recommend using it. Check codes, check and make sure power mode matches actual ignition switch position.
Tom, I really hope this helps.
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Thanks and good luck
Pawl
