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Good afternoon,
I have a 2006 Mustang GT Convertible that I have had a couple issues with recently. Initially, I have had a parasitic draw of about 110 milliamps noted with an inline amp meter. I have tried voltage drop test, pulled fuses and relays, and can't find anything drawing current in the main fuse box or the smart junction box. I even unplugged the PCM with no change. So, I thought I am going to have to live with it. It will run the battery down in about a week if I don't drive it. About 8 months ago I replaced the smart junction box (SJB) because the door locks or trunk electronic release would not function. Everything was fine until today. I pulled the car out of the garage and parked it. When I went to start it up it would come out of park several lights on the instrument cluster were illuminated. I ran the codes and I had B1676-60 (JEM) code, ABS U1900-E0, and several PCM codes PO 462, P1000, P1464, P2067, P1000-FF. Several modules were offline as well so I started where you should always start is with powers and grounds. Most of the codes seem to be related to the SJB so I started there. I had kept my old SJB so I went ahead and put it back on and the everything came back to life with exception of the power door locks and the trunk lock issue which was the reason I swapped the original one in the first place. I guess my question is could there be something with the parasitic draw that could be causing the SJB to fail? I'm wondering if there is rub point on the chassis that a power wire prior to a fuse could be causing a short to ground causing a parasitic draw. All Data does not speak much to what is acceptable with a parasitic draw and the internet is all over the place with what is acceptable. One may not be related to the other but I appreciate a second opinion. The replacement SBJ was a used one, and it could have been at the end of its life. I'm a little hesitant to buy a new or remanufactured one given how expensive these are and not understanding the cause. I don't want to be a parts changer!
Thanks,
David Conley
As you have found out smart junction boxes are not all that smart. How they fail is usually directly related to how they are designed, but usually comes down to a bad connection, either is a circuit busbar not making connection due to vibration or corrosion (green crusties), mating connector pin loose (low mating tension) and / or corroded, or a crack in a PCB bus bar solder joint. You seem to have a hard fault with your old smart junction box. This would be the easier one to fix in my opinion. Maybe you can take apart the bad used one to see how the junction box is design relative to the hard fault and how the circuit is routed, then you can get an idea of how to troubleshoot the old one, and what you have to do to repair and reassemble.
Thank you for your reply. There are several methods to track parasitic draws, but I chose the method of putting a voltmeter in series and disconnecting the bulk connectors on the smart junction box one at a time. Oddly enough when I disconnected the c2280h connector the amp draw dropped from 130 milliamps to zero. Given I pulled all the fuses and relays prior to this in earlier testing and the amp draw never dropped im left to assume that there is a power feed going to ground between the battery and the fuse. I pulled the bulk head connector from the SJB and back probed each connector. I did a resistance test and found that the brake pedal position switch signal had 1.753 ohms of resistance. So, I disconnected the brake pedal position switch and even the break light switch but the resistance value remains the same. I left to wonder if the circuit is going to ground prior to going back to the SJB.
You really should try to work through the (relevant) codes that you have with a view to fix this first. They should give you clues and diagnostic direction.
Get access to factory diagrams and guided procedures - they will help !
As for pulling fuses to find a drain then you are wrong to pull fuses, that just makes the job harder !!
"" Several modules were offline as well so I started where you should always start is with powers and grounds. ""
We see "Powers & Grounds" mentioned everywhere as a starting point - Which is great as I do that too.
First they DO need to be LOAD tested and then there is never any mention of "Current"
Where components, when switched on, should be pulling a load I think it is wise to throw an Amp Clamp around the wire and take a reading of the current draw - it may well hold good diagnostic value ?
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