ECU Challenge

[newey108]

Hi all,
I've got a 2005 LeSabre Custom that has a really tricky problem that dealerships haven't been able to answer for me. Twice now, the car has not been able to start. Turn the key and nothing happens - at all. Windows, locks, trunk release, instrument cluster, and dome lights not working - as if the battery were dead. However, headlights, horn, and blower motor work perfectly. Battery reads good. There is a Service Engine Soon light on but my ECU scanner won't connect at all.
Here's the fun part - Being my fidgety self, I pressed the eject button on the CD player. Suddenly, everything popped on - dashboard, cd player, engine able to start, and the trunk opened. I'd say this was coincidence but the same thing happened a few days later and the same solution worked. Can anyone explain why the ECU would be "stuck" like this until fiddling with the CD player? After the engine started, my scanner had no problem connecting to the ECU. No fault codes are stored. There are no aftermarket products on the car and no remote starter.

 

[ryenie]

Pretty sure the same fuse for the radio is used to power the dlc connector. Not sure how ejecting a cd would interfere with it though. Maybe check the Body & ALDL fuses in the rear fuse box, they seem to be connected to both the connector and the radio

 

[NFortin198]

I've had factory radios and aftermarket radios short out inside and not even know. The latest was last summer was with a factory radio. I had a problem of my battery becoming dead overnight. I would jump it and the car would be fine all day, but the next day it would be dead again. I went and replaced the battery and all was well for about six months and I started having the same problem again. the problem went on for about two weeks then went away for about a week. At that time, whenever I tried to start the car, or turn the radio on or off, I got a loud popping sound through the speakers. I got tired of hearing the popping so I swapped it out with one from the local parts yard, and ever since, I've had no more problems. I still had the original radio and took it apart and found a couple of wires, the main power and the memory power wires were rubbed bare by the movement of the CD table and it was grounding out at times.

Try just disconnecting the radio for a couple of days and see if the problem disappears.

 

[bigsky]

Pretty sure the same fuse for the radio is used to power the dlc connector. Not sure how ejecting a cd would interfere with it though. Maybe check the Body & ALDL fuses in the rear fuse box, they seem to be connected to both the connector and the radio

Maybe a short in that rear fuse box...??

 

[ryenie]

I would think a short in the radio, I think a short in the fuse box would lead to blown fuses.

 

[MelsRegal]

Was the service engine soon light on when you took the vehicle to the dealer?

 

[NFortin198]

You can have a short anywhere in an electrical system and not blow a fuse as long as there is sufficient resistance present between positive and negative. Example: The circuit contains a switch and a light bulb. Does the fuse blow when you turn on the light? No, because there is sufficient resistance in the bulb filament. When you turn on something, your basically connecting positive to negative, creating a short, the only thing that prevents the fuse from blowing is the resistance created by the item turned on.

 

[ryenie]

I would unplug the stereo and see what happens as mentioned above, and check your fuses. The radio is powered from two seperate fuses, one fuse could be blown, and is bypassed (backfed) voltage from the stereo once you hit eject button.

You can have a short anywhere in an electrical system and not blow a fuse as long as there is sufficient resistance present between positive and negative. Example: The circuit contains a switch and a light bulb. Does the fuse blow when you turn on the light? No, because there is sufficient resistance in the bulb filament. When you turn on something, your basically connecting positive to negative, creating a short, the only thing that prevents the fuse from blowing is the resistance created by the item turned on.

You can have three conditions that effect the circuit. An opened circuit, a short to ground, and a short to another wire. An opened circuit will not blow the fuse because current cannot flow throw an open circuit. A short to ground will blow the fuse instantly. A short to another wire (most likely from 2 wires melting together) may or may not blow the related fuses depends on which wires got melted together. A 12v feed crossing into a 5v reference wire will have different affect vs. a 12v feed wire melted to another 12v feed wire. Closing the circuit and a short in the circuit are not the same thing. The amount of amps drawn is relative to the resistance in the circuit. The resistance of the bulb isn't what keeps the fuse from blowing, it's the amperage rating of the fuse vs. the amps drawn by the circuit, not the presence of resistance in the circuit that determines if the fuse will blow.