Weird/extremely annoying electrical problem.. need help!
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Junior Member
Joined: Oct 2009
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From: long island, NY
c240
Weird/extremely annoying electrical problem.. need help!
Okay so this has been going on for about a year now but have been to lazy to address it. So when i have my headlamps on (even just in city lamp mode) my passenger side door does not want to function what so ever. When the lights are turned on the window will not actuate, turning signal on mirror will not work nor will the auto dim feature on the mirrors glass that blocks out the glare from other people headlights. I know it must be a short or something but am not sure where to start looking. Please help me out its very annoying having people in the car at night and having to say "oh yeah, my window doesnt work at night.."
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Joined: Jan 2005
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From: Orange County
2005 C Wagon (No snickering please!)
When current flows in the headlight circuit the CANbus signal does not reach the passenger door module is a strange flaw. I am not sure a short between wires can do this. Any short to the CANbus would affect all consumers on the bus.
Just a wild guess here, it might be a loose ground connection causing headlight current to flow through the passenger door module interfering with it's ability to "listen" to the CANbus. Ground points are a screw post coming out of the chassis with one or more usually brown wires connected via ring lugs. The ring lugs should be clean, shiney, and clamped tightly by the nut. A loose or corroded connection can cause headlight current not to be connected to ground, and the current then flows backward through the door module.
It could also be a defect in the processor/firmware of the front SAM that causes the undesired operation you observe. Replacement or a reman front SAM would be needed.
A little poking around with a voltmeter on the pins of the passenger door module might lead to the culprit. If any of the brown wires has more than a few millivolts to ground with the headlights on, but goes away with the lights off, you need to make sure all ground posts have a low impedence path to the chassis. Also check the battery negative connection and cable to chassis.
Good luck.
Just a wild guess here, it might be a loose ground connection causing headlight current to flow through the passenger door module interfering with it's ability to "listen" to the CANbus. Ground points are a screw post coming out of the chassis with one or more usually brown wires connected via ring lugs. The ring lugs should be clean, shiney, and clamped tightly by the nut. A loose or corroded connection can cause headlight current not to be connected to ground, and the current then flows backward through the door module.
It could also be a defect in the processor/firmware of the front SAM that causes the undesired operation you observe. Replacement or a reman front SAM would be needed.
A little poking around with a voltmeter on the pins of the passenger door module might lead to the culprit. If any of the brown wires has more than a few millivolts to ground with the headlights on, but goes away with the lights off, you need to make sure all ground posts have a low impedence path to the chassis. Also check the battery negative connection and cable to chassis.
Good luck.
