Looking at the wiring diagram for the 2007 FJC it looks like A-TRAC can be used with the rear locker engaged by disconnecting the signal wire betwen the Transfer Indicator Switch on the rear differential and the Skid Control ECU. There is a possiblility that it could set a code C1248 (open circuit in rear differential lock) in the VSC system but the DTC detecting condition seems unlikely in normal 4-wheling situations: "At vehicle speed of 31mph or more, 3 seconds elapse after rear differential changes from free to lock".
I don't have one of these FJ Cruisers (yet), does somebody want to try this hack on their own? The easiest place to disconnect this circuit looks to be at connector LA2, pin 11 in the left kick panel. It will be a light blue/yellow wire. If this hack works like I hope it will, the ABS and VSC OFF warning lights won't illuminate when the rear diff lock is turned on and the slip indicator light will only blink when the A-TRAC system is controlling wheelspin.
5/19/2006
An update with corrected information on the A-TRAC+rear locker hack. Disregard the wiring instructions above and use the update below.
I incorrectly assumed the Skid Control ECU supplied the signal voltage to the diff lock position switch, and then to ground. The signal voltage actually comes through the rear diff lock indicator LED in the combination meter, reaching ground at the diff lock position switch. The Skid Control ECU simply reads the 12v or 0v signal. No reference voltage is supplied by the Skid ECU to the light blue/yellow wire.
There are several ways of making this work, the key is to disconnect the Skid Control ECU from the rear diff indicator LED/switch circuit and supply battery voltage to the Skid Control ECU at connector A5, pin 1 when the ignition is on.
A possible way of making this work is to disconnect the light blue/yellow wire at connector LA2 and put a jumper wire at the Skid Control ECU (master cylinder and pump) between connector A4, pin 26 (light blue/yellow wire) and Connector A5, pin 1 (black/orange wire) to supply the 12v signal with the key on.
I don't have one of these FJ Cruisers (yet), does somebody want to try this hack on their own? The easiest place to disconnect this circuit looks to be at connector LA2, pin 11 in the left kick panel. It will be a light blue/yellow wire. If this hack works like I hope it will, the ABS and VSC OFF warning lights won't illuminate when the rear diff lock is turned on and the slip indicator light will only blink when the A-TRAC system is controlling wheelspin.
5/19/2006
An update with corrected information on the A-TRAC+rear locker hack. Disregard the wiring instructions above and use the update below.
I incorrectly assumed the Skid Control ECU supplied the signal voltage to the diff lock position switch, and then to ground. The signal voltage actually comes through the rear diff lock indicator LED in the combination meter, reaching ground at the diff lock position switch. The Skid Control ECU simply reads the 12v or 0v signal. No reference voltage is supplied by the Skid ECU to the light blue/yellow wire.
There are several ways of making this work, the key is to disconnect the Skid Control ECU from the rear diff indicator LED/switch circuit and supply battery voltage to the Skid Control ECU at connector A5, pin 1 when the ignition is on.
A possible way of making this work is to disconnect the light blue/yellow wire at connector LA2 and put a jumper wire at the Skid Control ECU (master cylinder and pump) between connector A4, pin 26 (light blue/yellow wire) and Connector A5, pin 1 (black/orange wire) to supply the 12v signal with the key on.
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