CAN THE UNLOCK/UNLOCK RELAYS IN THE SMART JUNCTION BOX BE TESTED AND HOW?

  • Tiny
  • mfoss
  • 2005 Ford Mustang
  • 120,000 miles

My passenger power lock failed. The actuator motor was constantly running, whining like the gears were stripped. I replaced the actuator and found the lock constantly going into an unlock position and the door could not be locked. When I tested the two connections to the actuator, the output was at a constant 12V. Changing the the position of the lock/unlock switch did not alter the signal at the actuator(there was no change in polarity and the 12 vdc was constant). The left door works fine. I now believe the problem is now, and was originally, coming from the "smart junction box". My knowledge of this box is nill. Do you believe my smart junction box is the source of the problem? Can I trouble shoot the lock/unlock relays shown in the smart junction box for a 2005 mustang.

Saturday, September 8th, 2012 AT 10:00 PM

4 Answers

  • Tiny
  • caradiodoc
  • Expert
  • 25,298 posts

By they sure add problems when they add complexity, huh? The fastest thing to do if you suspect a sticking relay is to just swap a few around, then see if something else is affected. The computer is a good suspect too but it's not unheard of for a relay to stick if the contacts arc enough to weld themselves together.

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Saturday, September 8th, 2012 AT 10:11 PM
  • Tiny
  • KHLow2008
  • Expert
  • 41,976 posts

If the left door is working correctly, I believe the passenger unlock relay is the culprit.

When locks are in a state of idle, both wires would have battery voltage. When unlock signal is received, the relay wuld be triggerred to ground the Light Blue wire.

Remove the relay and test the Light Blue wire for continuity to ground. If continuity exist, the control unit is faulty.

These are "A" relays and you should not be swapping with the main door lock relay. Only sway with the driver door unlock relay and test if problem is also transferred.

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Sunday, September 9th, 2012 AT 11:51 AM
  • Tiny
  • mfoss
  • Member

Thanks guys. This was helpful. I'll try to find a layout of the SJB to identify the location of the "A" relays and swap them around.

Mike Foss

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Monday, September 10th, 2012 AT 2:37 AM
  • Tiny
  • KHLow2008
  • Expert
  • 41,976 posts

Sorry I could not find any reference to the relays on the SJB. It looks like the relay are incorporated into the it therefore you would not be able to swap them.

If you are able to get a scan, check for Body Control Module trouble codes. It can help in diagnosing the problem.

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Monday, September 10th, 2012 AT 5:28 PM

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