I've never had this happen or heard of it happening.

But I'm interested it what you discover!

 

Sounds like a problem with the sensor. Have you had any axle work done on it recently?

 

had the cover off a few moths ago to replace rotted air fitting. nothing else was disturbed. I just find it odd that driving around town and speeds under 65mph its fine. the wiring going to the sensor is fine. I was going to pull the rear cover, but recent shoulder surgery puts a damper on things.

 

Were you in the radio or the HVAC controls? I'd take a look at the wires in the switch panel. A mouse or something could have done some damage to either the wires or the switch itself. And try going into 4lo and seeing if engaging and disengaging the lockers clears it up.

 

Folks have had problems when fill plug is overtightened. Maybe open and check not overfilled with fluid and then retighten not as snug and hit the highway. Seems if it were a wiring issue it would be a problem over bumpy roads not speed. i'm thinking pressure on the sensor. Maybe get a friend to check this, speedy recovery on the shoulder.

 

Is it a fast or slow flash?


This is from the FSM...

• Front Lock Request/Feedback Mismatch - Each time the cluster detects that the inputs from the axle lock switch (request) on the front axle lock request circuit and from the front locker indicator switch (feedback) on the front locker indicator switch sense circuit are mismatched, the front lock indicator flashes on and off at a slow rate. This condition occurs when the lock request is active but the axle locker remains disengaged, or when the lock request is inactive but the axle locker remains engaged. The indicator continues to flash until the request and the feedback are matching.

• Key-In Ignition Switch Input - Each time the cluster detects that the key has been removed from the ignition lock cylinder (key-in ignition switch open = key is not in ignition switch) while the front axle lock request is still active, the front lock indicator flashes at a fast rate and three chime tones are sounded. The indicator will continue to flash at this rate until the key is replaced in the ignition lock cylinder (key-in ignition switch closed = key is in ignition switch) while the front axle lock request is still active, or until the front axle lock request input is deactivated, whichever occurs first.

 

Is it a fast or slow flash?

This is from the FSM...

• Front Lock Request/Feedback Mismatch - Each time the cluster detects that the inputs from the axle lock switch (request) on the front axle lock request circuit and from the front locker indicator switch (feedback) on the front locker indicator switch sense circuit are mismatched, the front lock indicator flashes on and off at a slow rate. This condition occurs when the lock request is active but the axle locker remains disengaged, or when the lock request is inactive but the axle locker remains engaged. The indicator continues to flash until the request and the feedback are matching.

• Key-In Ignition Switch Input - Each time the cluster detects that the key has been removed from the ignition lock cylinder (key-in ignition switch open = key is not in ignition switch) while the front axle lock request is still active, the front lock indicator flashes at a fast rate and three chime tones are sounded. The indicator will continue to flash at this rate until the key is replaced in the ignition lock cylinder (key-in ignition switch closed = key is in ignition switch) while the front axle lock request is still active, or until the front axle lock request input is deactivated, whichever occurs first.

It's the rear axle lock and it flashes fast. Around town, no problem. Once I get on the highway and hit 65-70mph the rear lock starts flashing. I can come to a stop and the like goes out. I hit 65mph and it comes on again. I don't think its an electrical issue. I have checked the wiring at the rear sensor, around the rear axle and up the frame rail. I am wondering if something is going on inside the diff.

 

Whatever you do don't take that sensor out. It doesn't just screw back in. It has to go behind the locker ring. just FYI

 

Before you remove the cover, try backing the fill plug out a quarter turn or so and test drive.

 

ok, I'll give it a try and see what happens.

 

Since the FSM suggests the fast flash is caused by ignition key being removed, next time it happens try pushing your key in to see if that stops it. It could be an indication of a worn ignition key cylinder. Why it would only do it at speed if that were the case I don't know.

 

I'll give a try and see what happens. I'm starting to think there might be something going on inside the rear diff.

 

Thank you for the advice about the ignition switch. I was pulling my hair out trying to figure out what was going on! I had recently replaced the passenger side frame rail and while I had the chance I bought a transmission kit which included a filter, gasket, shift module and both speed sensors. My transmission was having a slight slip going into OD only! So I thought my transmission work was the cause for the axle lock issue. In the past I have had the vacuum hoses to lock pumps split causing the issue. You hit the nail on the head when you mentioned the ignition switch because about a year ago I had to change parts of the switch because truck wouldn’t start. I tried to be cheap and buy an aftermarket replacement but it was never right after that. I would sometimes have to push key In further to get radio to turn on. Today I took key cylinder out and added a very small piece of plastic in the hole on the end of the cylinder that pushes in the plastic pin in the ignition switch. Apparently the aftermarket one was a little shorter than original one! Thanks again!