In the past 15 years, Kia four-wheel-drive (4WD) and
all-wheel drive (AWD) systems have evolved from vacuum hubs and manual shifting
transfer cases to fully electronic systems that use magnetic clutches for
push-button operation. While you may never have to replace the entire transfer
case or transmission on the popular Sportage and Sorento SUVs, you will have to
replace hubs, sensors and solenoids on your customers’ vehicles. In this
article, we’ll start with the early systems on the 2000 Sportage.
The most common complaint you’ll encounter is no 4WD operation,
which can usually be traced to problems with the vacuum-actuated front hubs.
Kia requires that the driver shift the transfer case into four-wheel-drive,
choosing either high- or low-range gearing. The driver must then flip a switch
that opens a vacuum-control valve, sending vacuum to the locking front hubs and
engaging them to the drive axles. If there’s a weak link in the system, it’s
The hubs can cause a couple of problems. The first, and most
common, is no engagement. Many times, these troubles can be traced to the
vacuum supply, rather than a mechanical problem with the hubs themselves. The
first step is to be sure you have vacuum at the hubs with 4WD engaged and the
engine running. If not, work backward looking for the vacuum leak; a convenient
test point is the “T” fitting by the master cylinder where the lines branch off
to the left and right sides. This “T” is downstream of the control solenoid and
vacuum storage tank, so if you have vacuum here, you should have it at the
Many times, the problem is as simple as broken or
disconnected vacuum hoses leading to the hub. But, there have been reports of
problems with the steel lines running to the wheels. Over the years, these
lines can rust, restricting flow and, in the worst cases, causing leaks. There
are updated parts available, and Kia has issued a TSB on the subject (see
sidebar below), but line replacement can be a tedious task. Many techs
report good success with alternate methods of repair, but you’ll have to make the
choice as to what’s the best course of action for your situation.
Another problem you can run into with the hubs involves
engagement when it’s not called for. Usually described as a noise, in this case
the hubs are sticking, and the wheels are engaging and disengaging the drive,
the axles and front differential while the transfer case is in the
two-wheel-drive position. Many times, simply backing up the truck will take
care of this problem, but often it’s an indication that the hubs should come
apart to be cleaned and lubed.
Depending on the condition of the original units,
replacement hubs may be in order. In the case of the Sportage, road grime
that’s finding its way into the hub through the previously discussed vacuum
system can cause this problem. If the 4WD isn’t used very often, the broken or
disconnected vacuum lines could have been overlooked for quite a while.
Should you find yourself in the position where replacement
hubs are required, or if the customer values reliability over convenience,
consider changing over to the almost-bulletproof aftermarket manually operated
These units provide a low-cost alternative to the automatic
units and, while they require the driver to lock the hubs when 4WD is
anticipated or required, many customers find it an attractive alternative.
If you do go with the manual hubs, be sure to seal any of
the vacuum fittings to prevent debris from getting into the hubs, and
disconnect the supply solenoid to prevent a manifold leak when 4WD is selected.
It’s also a good time to service the wheel bearings or, at the very least, make
any bearing adjustment that’s required.
The rest of the 4WD system on these vehicles presents more
service opportunities than diagnostic challenges. Be sure to figure on
changing the fluid in both differentials as well as the transfer case when
doing a major service on a Sportage. Of course, any work on the hubs will have
you also checking the brakes.
4WD & AWD ON LATE-MODEL KIAS
Looking at the later-model 4WD Kias, we see them moving away
from locking hubs that engage the 4WD, and moving toward systems that de-couple
the 4WD differential from the primary drive.
After a short hiatus, the reinvented Sportage was back on
the market in 2005. Kia made big changes, one of which was going with a lighter
duty, crossover-type FWD platform vehicle that engages the rear wheels to
provide AWD as needed with a driver-controlled, lock-up option.
By looking at various sensors, the control unit decides when
torque will be delivered to the rear wheels and at what percentage. By looking
at individual wheel speeds and throttle position, brake input and steering
angle, the control module will send a command to the rear differential-mounted
coupler, applying the appropriate pressure to the internal clutch pack for the
While the coupler handles the varying load, the continuously
engaged, transaxle-mounted transfer case does the job of keeping the driveshaft
If the conditions require 4WD operation, the driver can
choose to lock into FWD, providing the maximum 50/50 split to both axles.
Designed for low-speed operation, the control unit will begin to disable the
lock at 18 mph, and, at 25 mph, the lock system is fully disabled. As speeds
come down, the lock feature will re-engage. Being speed dependent, if there is
a problem with the wheel speed sensors, the lock option is disabled.
When it comes to potential problems, most will be mechanical
issues, noises or vibrations. Instead of two CV axles there are four, and you
have to consider the driveshaft as the shakes and noises are diagnosed. The
wheel bearings and hubs are no different than what we see on any 4WD or AWD
vehicle. The only serviceable items in the coupler are the bearings.
If you’re faced with a blinking 4WD lamp on the dash, or a
suspect a problem with the system, it will be difficult to go much further
without a scan tool that has enhanced software that will give you access to
codes and data. Even with the very good information on the free Kia service
information site (www.kiatechinfo.com), you would be hard-pressed to have a
successful outcome without the tooling.
With the transfer case mounted to the transaxle, when it
comes to maintenance on the system, it’s easy for an inexperienced tech to
think they share lubrication. That is not the case with the Kia and it’s
important that the fluid level in the transfer case be checked and replaced on
the same interval as you recommend for the transaxle.
THE SORENTO SYSTEM
The Kia Sorento models up to 2009 offered both a part-time
on-demand system, as well as an optional full-time AWD system. We’ll take a
look at the part-time system that Kia refers to as “Electronic Shift Transfer
(EST),” that uses an electrically controlled transfer case as well as an air
pump system to engage the front axle. This allows for shifting “on the fly,”
from 2WD to 4WD, applying a fixed amount of torque. When in 2WD, the front
“free running differential” is decoupled from the driveshaft, eliminating any
noise or vibration while also eliminating the need for locking hubs.
When the 4WD switch is selected, an electric air pump is
commanded on to pressurize the coupler, engaging the front differential pinion
to the driveshaft, while the transfer case-mounted motor moves the shift forks.
Then, finally, the magnetic clutch closes, providing torque to the front
driveshaft. This is all controlled and monitored by the transfer case control
module (TCCM). With either system, the vehicle has to be stopped to engage 4WD
Like the Sportage, if the TCCM sees a problem, the 4WD lamp
will flash. No tool is required to retrieve codes with the EST system. When no
codes are present, turning the key on should result in the 4WD lamp lighting
for 0.6 seconds as a bulb check, and then it will turn off. If codes are present, the bulb check will be
followed by a flash code in three seconds. There are seven codes available
using ones and zeros. A short 0.5-second flash represents a zero, while a
one-second flash indicates a one. The code will repeat itself three times; for
example two shorts and one long flash is 001 (see flash diagram above).
There have been some problems with both the transfer case
motor and air pump used for the differential coupler. That’s not too
surprising, considering that the system spends most of the time in two-wheel
operation. Sometimes, a simple tap on the transfer case shift motor or air pump
will shorten the diagnostic process. Of course, a motor that comes back to life
with a tap is certainly suspect and should be replaced, but that’s between you
and the customer.
If you do find yourself diagnosing the front differential
coupler, keep in mind that it operates on 5-8 psi, so don’t just put the shop
air to it. When it comes to maintenance, the transfer case fluid is critical to
long bearing and clutch life, so much so that transfer case oil pumps are used
to keep it moving; be sure it’s checked and changed with the recommended fluid.
On all 4WD or AWD systems, tire size conformity is critical.
The first diagnostic step for any problem should be to measure tire
circumference. While the method doesn’t matter (we measure circumference with a
narrow tape), just be sure they are the same size. Ideally, they will all be
within 1/16”. Much more than that should bring up the discussion of tire
replacement, especially if the problem involves binding or engagement issues in
an on-demand system that appears to operate as expected.
On automatic or AWD systems, tire size is even
more critical as the system sees the speed differential of the tire size as
slippage and adjusts accordingly. It’s easy to see how this would shorten the
life of the clutches. This is why it’s so important that tires be replaced only
in sets of four.
4WD Control Vacuum Line
Four-wheel-drive mode inoperative (diagnosed either during
or after replacing knuckles and hub seals) due to insufficient vacuum being
applied to the hubs. In some cases, moisture has entered the vacuum system and
the vacuum lines have become corroded, plugged or have developed a leak.
Verify that with the 4WD mode selected, vacuum is present at
the T-fitting downstream from the solenoid. If not, diagnose and repair as
required. Otherwise, use the following procedure to replace the vacuum lines:
Note: Refer to section 4360 of the parts catalog for part
numbers, etc. Procedure applies to the right-side line; the left side needs no
1. Disconnect and remove the battery and battery tray.
2. Leaving ground cables attached, remove the clamp bracket
from the battery tray bottom and move it out of the way.
3. Remove the plastic air resonator and disconnect the
throttle cable (plus A/T control cable, if equipped).
4. Disconnect the MAF and IAC connectors, and the 6 mm bolt
holding the DLC and MAF brackets to the air cleaner housing.
5. Disconnect the air intake tube from the throttle body,
and the MAF sensor from the air filter housing.
6. Remove the tube, duct and sensor assembly and set aside.
7. Loosen the rear engine hanger bracket and front surge
tank support bracket.
8. Disconnect the coolant lines from the throttle body, or
(alternatively) remove the throttle body from the surge tank but leave the
coolant lines attached. Remove the surge tank.
9. Cover the intake to prevent anything from falling in.
10. Mark the steering column shaft and coupling for later
reference. See Photo 1 below.
11. Loosen the clamps on both sides of the coupling and
slide the coupling back on the intermediate shaft, disconnecting it from the
12. Disconnect the vacuum hoses in the right wheel well and
from the T-fitting below the 4WD solenoid on the driver’s side of the engine
13. Pry the vacuum line loose from the four plastic retainer
clips; two on the bulkhead, two on the inner wheel wells.
14. Using the slack in the harness and carefully bending the
vacuum line only as necessary, free the line from behind the harness bundle
against the RF inner wheel well.
15. Free the vacuum line from behind the brake line attached
to the outboard position of the differential pressure valve.
Note: Try leaving the old line intact while removing it and
carefully observe the “route” you use to get it out. This will serve as
“practice” that will come in handy when you install the new one.
16. Starting from the driver’s side, free up the old line
and move it up until it clears the cylinder head at the location of rear engine
hanger. Move and “snake” the line carefully as required to free it up and pull
17. Install the new line the same way, and assemble
everything in reverse order. Observe the reference mark on steering shaft when
18. Test-drive and check 4WD operation.
Courtesy of Kia Motors America.
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