Hey all, we just bought a used '99 5.4 Exped, and living here in CO I have a 4x4 system question. It would seem that the auto-awd system is very slow to engage the front wheels...like a full 4-5 seconds slow...

Is this a normal thing from these trucks? Or should it engage much more quickly than I'm seeing? It is causing us a bit of grief as we depend on our 4x4 to keep us out of trouble, especially on slippery uphills, etc. I'm hoping this is correctable, as having to switch to 4-high whenever we need 4x4 is kind of a pain...especially for my wife.

Thanks all!

Sam

 

I should also add that we had a ABS light come on today as well...and it went back out with a shut down/restart. It would seem that aawd mode does not work at all with the ABS light on...

Is there a way to manually pull codes for this if there is one? Also, could an ABS wheel sensor, or maybe mud/dirt in that area of the brakes be causing my issues, as if the system doesn't know my rear wheels are slipping?

Anyone? Anyone? Bueller? Bueller?



Thanks again

Sam

 

The rear wheel sensor is mounted on top of the differntial and is a source of problems. There are codes that can be pulled from the ABS system but it takes a scanner that is set up for that, a standard OBDII scanner will not read it. The rear sensor is very easy to change with only one bolt and a single plug in to deal with. The part is about $20 and available at most part stores.

 

So what you are saying is...at 150K miles, I should just spend the money and replace the part! I don't have access to a scanner for that, unless my local parts store also has that. I know it is not a standard OBDII scanner that does it, but it is still scanned from the OBDII port, correct?

 

Oh, last question...is that ABS sensor also the source of the auto-4x4 problems I'm having? Or could it be?

 

The ABS scanner does use the same port as the OBDII scanner. It is unlikley that a parts store would have one for ABS. It could indeed affect your Auto 4x4 as I believe that is how the computer detects slip when the rear wheels are spinning faster than the front. As I changed the one on my truck at about 60k and I changed one on my neighbors 2000 Exploder, along with the other posts about the ABS light coming on, I would say it is a good gamble to take considering the time and money required.

 

Awesome man, done deal.

Now I need to replace the lines and O-rings to the remote oil filter...or oil dripper as it is now. :\ ...short list continues to adjusting the shifter cable since D is now 2. And also figuring out why my heat control **** sometimes doesn't let me all the way to cold or hot...feels like the control itself might be stripped...oh well...the pleasures of a new to me vehicle!

 

If your shifter feels all right otherwise and you can shift into all your gears you most likley need to adjust the shift indicator and not the cable. Look for a string (white I think) attached to your shift lever, on there I think you will find a little wheel that can be turned to make the adjustment. As for the oil leak I haven't had to deal with that one yet, do a search for info on that. I had a **** for my temperature control split where it pushes onto the shaft. You can pull it off and check it out, seems like it was kind of pricey at the dealer but did not want a used one on its way to splitting.

 

The automatic 4-wheel drive A4WD system is a full time 4-wheel drive system with an electronic shift 4x4 system that allows the operator to choose between three different 4x4 modes. The operator can switch between A4WD, and 4WD high mode at any speed, and 4WD low mode. To engage or disengage low range, the vehicle speed must be less than 5 kph (3 mph), the brake depressed, and the transmission must be in NEUTRAL.

In A4WD, the generic electronic module (GEM) varies the torque split between front and rear drivelines by controlling the transfer case clutch. The transfer case clutch allows for slight speed differences between the front and rear driveshafts which normally occurs when negotiating a corner on dry pavement. When the rear wheels are overpowered, the GEM detects this slip condition, and the duty cycle to the transfer case clutch is increased until the speed difference between driveshafts is reduced.

The 4WD mode switch is a rotary switch which allows the vehicle operator to choose between A4WD, 4WD high, and low range positions. There is no A4WD lamp, and the 4x4 lamp is controlled by the GEM and tells the owner that the vehicle is in 4x4 high mode. The LOW RANGE lamp is controlled by the PCM.

The vehicle speed signal is hardwired between the powertrain control module (PCM) and the GEM, speed control, overhead message center, air suspension, and EVO steering. The instrument cluster also receives the speed signal, but receives it over the standard corporate protocol (SCP) communication network. The PCM determines vehicle speed from the output shaft speed (OSS) sensor which is hardwired directly to the PCM.

The Hall effect sensors are mounted to the transfer case and are used to determine the speed of the front and rear driveshafts.

The shift motor sense plate, an integral part of the electric shift motor, is used to inform the GEM what mode the transfer case is actually in.

The digital transmission range (DTR) sensor, located on the left side of the transmission, informs the GEM of the transmission gear position.

The 4x4 shift motor relay is a module containing two relays which, under the control of the GEM, shift the transfer case shift motor between the three 4WD modes.

The torque on demand (TOD) relay is used to activate the A4WD clutch within the transfer case by the GEM. This relay controls the torque split between the front and rear axles.

The throttle position signal is hardwired from the PCM to the GEM. The GEM uses the throttle position to anticipate a rear wheel slip condition when the vehicle is in A4WD.

 

Thanks for the heads up, Craig!

 

Ummm...Thanks! That is honestly more info than I know what to do with...so I'm going to copy/paste in an email to my dad in CA who knows all this as well, and can translate for me! LOL!

 

It seems ok, though a couple times I wanted to put it in 2nd and had a hard time getting it there and had to wiggle it around...I may be having issues with both, but I will adjust the indicator first.

 

The 4WD mode switch is a rotary switch which allows the vehicle operator to choose between A4WD, 4WD high, and low range positions. There is no A4WD lamp, and the 4x4 lamp is controlled by the GEM and tells the owner that the vehicle is in 4x4 high mode. The LOW RANGE lamp is controlled by the PCM.

I have a A4WD lamp on mine.

 

ronk1969, how did you install a A4WD lamp in your Expedition?
Thanks ~Gage~

 

they have been there ever since i have had the expy. i have some pictures , but cannot figure out how to add them to the reply. if someone would help me out i will put them up for you