trader323 Posted June 30, 2017 Report Share Posted June 30, 2017 (edited) Hello everyone. On a 2007 MKX AWD, what was supposed to be a simple fuse check/swap has turned into a big problem. Potentially a really big problem The backlighting on some controls and buttons was not working. So I started checking fuses in the cabin fuse panel. I didn't find a blown fuse at first. So I decided to use a multi-meter to find out if there's any dead circuit. With a fuse removed, I inserted the multi-meter probes into the fuse ports. Suddenly the car started losing power, within seconds the lights on the dash were out and nothing powered by the battery will run. When I turn the key in the ignition I hear clicking but the no turn. The multimeter was on the DC volts setting by mistake. Is it possible that caused a short? When I measure the battery voltage now I get 7-8 Volts only. When the battery cable is disconnected I get close to 12 V again. Even trying to boost the car won't make it run. I have a loss of 4 volts and a major parasitic draw. Nothing runs or works in the car. Could the multi-meter cause such a short or failure? I hope I don't have to take our the entire fuse panel or have to replace it. Any suggestions will be appreciated. Edited June 30, 2017 by trader323 Quote Link to comment Share on other sites More sharing options...
enigma-2 Posted June 30, 2017 Report Share Posted June 30, 2017 Setting a VOM on volts puts the meter in series with the load (measuring current places a shunt in parallel across the load). The "fuse panel" is actually a computerized control module. My 'guess' is you placed a bolted short through the smart junction box (fuse box) and damaged it. I don't know of any way to test it to determine its condition. The failure of the back lighting could be a LED failure, corrosion or a wiring failure. If I'm not mistaken, all the car's back lighting is controlled by one fuse, therefore if any of the back lighting is working, the fuse is good. The feed runs to a single connection point and branches from there. LEDS do wear out over time, voltage spikes, heat, time all play a factor in their life. 1 Quote Link to comment Share on other sites More sharing options...
trader323 Posted June 30, 2017 Author Report Share Posted June 30, 2017 Thanks Enigma-2. That's what surprised me even, if I placed the VOM in series with the current, am I doing anything more than substituting for the fuse? I don't know if the the VOM could have allowed more than the 10A that would have burned the fuse but that's not likely. I didn't jam the probes in too strongly to cause a physical damage. I will be running some parasitic draw tests this weekend to see if I can isolate a problem circuit. I am holding out faint hope that the problem will be in some peripheral location and not the entire BCM. Installing and programming a BCM is not DYI job ... or is it. Quote Link to comment Share on other sites More sharing options...
akirby Posted June 30, 2017 Report Share Posted June 30, 2017 Have you tried leaving the battery disconnected for a couple of hours? Can't hurt. Quote Link to comment Share on other sites More sharing options...
trader323 Posted June 30, 2017 Author Report Share Posted June 30, 2017 Well the battery has been disconnected since last night. The short, if it is that, would have drawn it empty anyways. I will try again this afternoon, but that won't likely help. Quote Link to comment Share on other sites More sharing options...
trader323 Posted July 1, 2017 Author Report Share Posted July 1, 2017 (edited) Did a parasitic draw test. I could hear a light clicking noise coming from somewhere near the SJB. Started pulling out fuses one by one and the clicking noise stopped on a couple of them but only one caused a change in the multi-meter reading. Weirdly it corresponded to the right low beam which i am sure shouldn't have been on at the time. The battery was too weak so I boosted the car and tried starting it. And it started!! I hesitantly plugged in the right headlight fuse but the car kept running. Disconnected the booster cables and let engine run for another 10 minutes, no issues. I then turned the car off completely and pulled the key out and locked the doors. Then unlocked and started again and everything including the right low beams worked!! I then put in a fuse for the original puddle lights/backlighting issue and, guess what, they started working again. Not sure if I'll have issues later on, but for now I'm happy the car can at least start and seems to be problem free. These SJBs can certainly be unpredictable and may have logic to disable some circuits if they suspect an issue with them. So Akirby, you may have been right, all it needed was sometime in the dark to reset. It might also be a battery problem. It is 3 years old but other incidents/observations tell me it may need replacement. Batteries don't seem to last long on these cars up here. Happy Canada Day /4th of July!! Edited July 1, 2017 by trader323 1 Quote Link to comment Share on other sites More sharing options...
WWWPerfA_ZN0W Posted July 1, 2017 Report Share Posted July 1, 2017 Fingers crossed the fix lasts. Happy 4th!!! Quote Link to comment Share on other sites More sharing options...
enigma-2 Posted July 1, 2017 Report Share Posted July 1, 2017 ^Second that. Perhaps the computer just needed to be reset. 1 Quote Link to comment Share on other sites More sharing options...
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