Hello, I have a 1997 F150 4.6L Lariat 4x4 super cab... Had some mud and was using 4 wheel drive alot. Everything was working perfectly in 4 hi until like a f**k I decided to try 4 lo. The 4 wheel drive is controled by a switch on the dash. While sitting still I switched it to 4 lo and started to drive off and heard a “klunk” sound. I stopped and backed up and nothing happened.
4x4high - 4x4 Dasch lamp is on, the drive is working properly
4x4low – dasch lamp is off, the electric motor is not handled exclusively drive
Now i only have 2 wheel drive, 4high which is working fine but no 4lo. The light on the dash doesnt come on either now. Any ideas? I've searched but really nothing comes up for this problem.
Any help appreciated

 

Most likely shift motor is shot.

 

Or GEM module.

 

the motor is OK

 

how to (GEM) diagnose?

 

Usually some other interior functions act strange: windows/locks work erratically, etc.

Search online for other symptoms.

Jim

 

The fact that 4H works tells you the GEM is requesting the case motor to move to it's first position, the firewall solenoid is transferring vacuum to the front axle actuator and the axle is locking together, so all these actions are good..
.
The difference with 4L is you need to be stopped, foot on brake and shifter in neutral. Dash switch in 4L tells the GEM to advance the case motor one more position, shifts the transfer case to a lower gear ratio and changes the transmission shift rpm and causes the GEM to light the 4L dash indicator.
Everything else is the same.
.
Did you apply 4L properly? Stopped, foot on brake and shifter in neutral all at the same time.
.
Did the case motor advance?
If no, the Gem could be the problem , the dash switch, the case motor or it's internal circuit board or harness.
Iv'e brought the operation down to a narrow area for you, enough to understand the operation and area the fault could be in..
Good luck.

 

still struggle with 4low