2019 4HI & 4Lo Lights Flashing!

Mine started doing it this morning. Fudge.

 

What a coincidence... I've been purposely messing around with the 4WD ECU and have learned a lot of things.

First off, Gen2 and Gen2.5 are different in how they change 4WD modes. With that said mine is a Gen2.5 and what I've learned only applies to that.

If and only if the 4HI/4LO is flashing, nothing else lighting up, then it has to do with something that is physically connected to the 4WD ECU. There are 2 connectors on the 4WD ECU:
1. Connector A25: connects to the ADD (motor, detection switches(which are actually transistors/diodes), shift knob, and CAN BUS
2. Connector A26: connects to the TC actuator (motor, detection switches) and Coil



I've been messing with A26 and discovered the following:
- If any one of these pins (SCC, TM1, TM2, TL1,Tl2, TL4, GTL) have an open (a break in the wire or at the pin) then 4HI/4LO will flash
- Moving wires around to see if the flashing will stop will not work because once it starts flashing it will not stop until the ignition is turned off. So if you're going to wiggle things around, then I suggest (with ignition off) wiggling one thing, then turn on the ignition (don't have to start the truck). If that doesn't stop the flashing, then turn off ignition, wiggle something else, then turn on ignition - rinse and repeat.
- The 4WD ECU expects certain voltages at each pin. If that voltage is not present upon ignition start, then you get flashed.

These are the voltage readings I got with the ignition on, in 2WD, and the connectors plugged in (only tested A26). TL1 - TL4 can be deceiving though because they are transistors/diodes with voltages on both ends.


The big difference between Gen2 and Gen2.5 is the Coil (SCC). It is a way to "shift on the fly" to 4WD even though both Gens did it. Gen2.5 energizes this coil (you'll get a 6 amp reading for 9-10 seconds on SCC) which squeezes clutch plates together (making that loud clunk) that engages the Lockup Drive, aligning the gears/spline, so that the Lockup Collar can be slid into place. Shifting to 4HI is a 2 step process.

TM1/TM2 is the TC actuator motor. When shifting to 4HI I noticed, on both, a momentary jump in voltage 12-14 volts. When shifting to 4LO I got the same thing. However, these momentary spikes do not correlate to how long the motor is actually turning. It seems like the voltage spike triggers something else to turn the motor for a specific amount of time/range. (Still trying to figure this out myself). When shifting from 4LO to 4HI and back to 2WD, the momentary triggers went to 0 volts but with a negative current of ~1.5 amps, which tells me it probably went to ground with the high voltage originating from the actuator.

So if you're having intermittent issues, then a wire is breaking/broken (somewhere between connector to connector) or there is a pin in the connector that is loose, or the crimp is coming loose, or the pin is breaking/broken where the wire is crimped onto.

I'm sure you would get similar results on the A25 connector, where an open pin can cause the flashing.

Post is all over the place, was just dumping what was in my head.
$.02

 

Has anyone found the issue to this? Mine started doing it in the summer and the dealership told me it could be an exposed wire in the harness by the driver side firewall. I think that’s a BS answer to get me to replace the harness. Any and all input is greatly appreciated

 

Still dealing with it here. My 4hi and 4lo are flashing pretty consistently but I can still shift into both with engagement. Not sure what’s causing the flashing.
Are you able to shift into 4hi or low?

 

My 2008 just started doing this when driving down rough washboard roads. Doesn't matter if I'm in 2wd or 4wd. After a few minutes on the rough road they will start flashing and the 4wd switch will not do anything. After turning the truck off and on again, everything is back to normal... Until another rough road.