TRAC Off Light + MIL + Cruise Control Dropouts + No ABS Lamp

By John Cribb

These are mysterious, but well known and related problems with MKIV Supra’s caused by cold solder joints or broken traces on certain printed circuit boards in the dash warning lamp clusters.



The Fix:


Tools Needed:


Warning Lamp cluster removal:


Now, looking up under the instrument cluster, notice there are five (5) screws. Remove these:


This upper trim piece with the left & right warning lamp pods & odometer can now be pulled away from the dash:


Very carefully pull this piece away from the dash until the connectors are exposed for the right & left warning lamp pods. Find the spring releases on these connectors and release the harness and unplug the assembly. Do not force anything here! Once you properly release the spring catches on the connectors, they should unplug fairly easily. Do not pull on the wires themselves, only the plugs & sockets:


Once the trim piece with lamp pods has been removed, it’s time to take the lamp pods off and disassemble. Here is a photo of the left hand pod where most of the problems occur:


Remove the black screws first, which hold the pod to the trim, then remove the brass screws which will expose the two printed circuit boards. Disassemble the unit.


Gently spread the boards apart to expose the solder connections. Note how the main connector for the module is mechanically fastened to the board by its solder joints – this is one weak spot, with the connections for the ribbon cable also being suspect:


Now, apply a thin coating of rosin core flux to all the exposed solder joints and “touch” each one with the soldering iron so that the solder becomes molten again and flows through the joint. Leave the iron on the joint only long enough to ensure the solder has reflowed, then remove it. Do not jar or move the assembly for at least 5-10 seconds after removing the iron, as this may result in a “cold” joint. If you have done this properly you should be rewarded with a shiny new solder joint. Note, it must be gleaming & shiny – if it looks dull, then you moved it while it was solidifying, didn’t heat it enough, or you forgot to use the rosin flux to keep the joint clean. The use of rosin flux is MANDATORY for this work. The high heat of soldering causes rapid oxidation of the metal – oxidation leads to poor bonding, and poor bonding means cold solder joints. If your joints are not shiny, you must do them again.

Repeat this process for each exposed solder joint, then clean the excess flux off the board with a clean rag or paper towel and inspect your work closely. Make sure all new solder joints are clean and shiny, and ensure that no joints have accidentally shorted together by “bridging”.

If you have access to a good light source and a magnifying glass, it may be useful to inspect the board traces closely for any evidence of cracking or breakage as some owners have reported problems with broken traces on their boards rather than just cold solder joints. If any broken traces are noted, the break can usually be bridged by applying a “very” small bit of solder at the point of the break. Keep in mind that less is best! Only apply a small bit of solder to the tip of the iron – not even enough to make a visible “drip” on the tip, then apply the tip to the broken trace and let the solder “heal” the break.


Once you are happy with this cluster, repeat the process for the right hand odometer cluster. Note how many more connections it has due to the display:


Finally, reassemble both Warning Lamp clusters in their pods and into the trim piece, reconnect the wiring harness and reinstall the trim piece into the dash. Note this trim piece has several pin & sleeve type locators on both the left & right sides, as well as the top of the gauge cluster. Make sure these pin & sleeve points are mated correctly as the piece will not fit otherwise and/or something will break. Replace the five (5) black trim screws, reconnect the negative battery terminal and you’re ready to test your work.

Start the car, noting that the ABS lamp will stay on in the left-hand pod for two seconds after the ignition is turned on (this is the ABS self test). After this, confirm that all warning lamps have extinguished and the car is running OK. Give both left & right pods a couple of sharp raps with your knuckles, or apply finger pressure and see if a MIL can be produced. If this procedure produced a MIL previously, and does not now, congratulations! Take the car for a spin, over some railroad tracks if possible, or other rough surface and continue to give the left & right pods some sharp raps and watching for MIL’s or other warning lamps.

If any new Warning Lamps or MIL’s are illuminated, you may have to disassemble the dash, pull out the instrument cluster, and resolder the joints on this assembly just as you did for the Warning Lamp pods.