have 2003 4x4 f250 with the 5.4 motor. 4x4 just stopped working pulled fuses and replaced with all new ones, pulled switch on dash and checked with a test light and no power for all 4 wires. have been trying to find a wiring diagram to locate the relay any ideas on the problem???

 

The dash switch won't necessarily have 12 volts on it anywhere. According to the wiring diagrams "VREF" is sent to the switch and is returned through resistors whose value depend on the switch position. I believe VREF is 5 volts but I'm not certain.

Measure for voltage between pin 2 and 3 on the plug at the switch. There should be at least some voltage there. If there isn't, then you have a fuse not supplying power to the 4WD control module, or the module itself is bad.

As near as I can tell, fuses 19, 31, 33 and 45 all supply power in some form to the 4WD control module. Check these with a test light or continuity meter. Also check the fuse bases to make sure they are tight and there is no corrosion. Fuses can be bad but not appear blown, which is why I suggest the test light or meter.

 

Ok I'll check that I dont know if its an indication for the module being bad but there is no light on that indicates 2wd or 4hi, 4lo

as far as the test light on the fuses i checked them all found one bad one but wasn't for the 4x4.

Any way that the relay it self is bad under the hood?
Thanks for the advice David

 

The most likely cause of a transfer case shift failure are the two shift relays under the hood. A common diagnostic procedure is to find the relays (two identical relays by themselves in a relay box on the drivers side firewall) and swap their positions. If this allows you to shift into 4WD but not out, then you know the problem is one of the relays and it's fairly inexpensive to replace both of them.

The next most common procedure is to put a test light between the two pins of the two wire connector on the shift motor at the transfer case. Have someone switch to 4WD with the key on and see if the test light flashes. This indicates power to the shift motor, and if the motor is getting power but not shifting it may have failed.

 

OK Thanks I'll give it a shot in the morning and let ya know thanks again.

 

ok well back to square one checked the relays and they were good. Checked the shift motor at the transfer case and they are good. Still no idea why there is no power to the switch on the dash, starting to check all the connections to look for corrosion and looking for broken wires now any other ideas?

 

I can't say I have a lot of ideas, but here goes.

I think what I would do would be to start looking at the 4WD Control Module itself. They have been known to go bad. You should find it on the firewall behind the glove box. Open the glove box, push in on the sides and it should open all the way, revealing the area behind it. The 4WD Control Module is back there.

I'm assuming my 2004 is similar enough to your 2003. I've attached the two connector diagrams for the 4WD control module. As well as one of the wiring diagrams for it.

I think the first thing I'd do is check all of the power and ground connections. Check for power on each pin indicated, and check resistance between the ground pins and a known good frame ground.

If all those test out good, I'd figure out some way to hook up a DVOM to pin 6 of connector C281b while it's connected to the module. If I'm reading it right, the module should ground pin 6 in order to activate the relay that shifts into 4WD.

 

subscribing

 

Ok I'll check that I dont know if its an indication for the module being bad but there is no light on that indicates 2wd or 4hi, 4lo



Just a thought but did you check the bulb, it may be the connection that you need to complete the circuit.