How do you fix Hyundai Terracan 2002 model with error code P1728 - EMC open/short to battery?

ok, must not be ASE rated mechanics???? sure.
please post the symptoms , I can not understand your post.
my guess is you mean the dash warning light with a kEY icon
is glowing, well that is the Immobilizer.
the operators guide covers all lights,. lost that?
using both keys as sold with car new??? lost the spare?

here is a DIY list, (my wild assumption)

1. Read the operators guide first (glove box)?
2. check all fuses for good (test them)
3. scan the PCM see if there are IMMO errors SKIM/SKIS etc.
4. the scan tool can show many errors, like wrong key, or comm errors or the skim module is dead or , gee the whole list of possible errors there covered in the fsm.
5. reset the battery , pull neg lug wait 15m, and put back. but may brick the radio, (it asking for codes) (or NAV if you have that)
6. that is about it DIY.

no scan tool?, no joy,,,, DIY.

I would suggest completely disconnecting the battery from the vehicle. Doing this might reset the system.

code p1123 refers to long term fuel trim--additive--mixture too rich===causes-- HO2S--fuel pressure --fuel system---mechanical fault---ECM
check all wires and connections. With the mechanical fault I would be revisiting all the items you removed to get to the rocker cover to ensure that all the hoses and wires were correctly replaced and that the gasket has not been mis -fitted or squashed out from under the cover at some point

SOLENOID POWERED?

To start with, a basic engine computer code reader will not connect to the body computer which is why they are not getting any codes.
The 4wd lights will not come on as long as the warning light is on, the system is disabled until it is fixed.
You may need someone with a professional scanner to connect to the body computer.

A/T(Automatic Transmission)Oil Temperature Warning Light

Yes it may be the wires are shorting or its actually the problem with instrument cluster.
Also get the vehicle scanned for any error codes stored in computer this will confirm whether is short circuit issue or actual problem:------
I suggest you few help links with accurate solutions to refer/go through:----Click the link below:------

Battery and brake Warning lights on Dash
http://alltypesofpartsreplacing.blogspot.com/2012/10/battery-and-brake-warning-lights-on-dash.html
--------------2002 Ford Windstar: Brake Warning Light ON dash? http://schematicsdiagram.blogspot.in/2012/06/2002-ford-windstar-brake-warning-light.html
-------------ABS & Brake warning lights remains steady on dash? http://schematicsdiagram.blogspot.com/2011/12/abs-brake-warning-lights-remains-steady.html
-----------Chevrolet Tahoe Hood open warning on dash and alarm sounds? http://schematicsdiagram.blogspot.com/2011/12/chevrolet-tahoe-hood-open-warning-on.html
-----------2005 Chevy Impala: Service Vehicle Soon Warning Light? http://whoisbyme.blogspot.in/2012/06/2005-chevy-impala-service-vehicle-soon.html -------------- Malfunction Indicator Light ON http://whoisbyme.blogspot.in/2012/06/malfunction-indicator-light-on.html
-----------Car Runs Fine But Check Engine light is ON?

http://whatisbyme.blogspot.in/2012/05/car-runs-fine-but-check-engine-light-is.html

----------
Check engine light with codes P2195 and P2197?

http://howtobyme.blogspot.in/2012/01/check-engine-light-with-codes-p2195-and.html

----------
How to Read Codes from Check Engine Light? http://schematicsdiagram.blogspot.com/2011/12/how-to-read-codes-from-check-engine.html
-------------These will help.Thanks.

Check this website, you find there fuse box diagram and description for Hyundai Terracan

Hyundai Terracan 2005 2007 fuse box diagram Auto Genius

P1728 EMC-Open/Short To Battery P1739 General Position Encoder Fault I would try to clear the faults with a scan tool. If they return take to the dealer for a more detailed fault analysis.

Here are all the possible problems which can turn on your ABS light.

C1101 Battery voltage over volt: 18V or more ○ ○ BR - 69
C1102 Battery voltage low volt: 9.5V or less ○ ○ BR - 69
C1200 FL wheel sensor: open or short to ground ○ ○ BR - 66
C1201 - Range/Performance: speed jump or damaged exciter ○ ○ BR - 67
C1202 - No signal: air-gap error or wrong excite ○ ○ BR - 68
C1203 FR wheel sensor: open or short to ground ○ ○ BR - 66
C1204 - Range/Performance: speed jump or damaged exciter ○ ○ BR - 67
C1205 - No signal excite: air-gap error or wrong excite ○ ○ BR - 68
C1206 RL wheel sensor: open or short to ground ○ ○ BR - 66
C1207 - Range/Performance: speed jump or damaged exciter ○ ○ BR - 67
C1208 - No signal excite: air-gap error or wrong excite ○ ○ BR - 68
C1209 RR wheel sensor: open or short to ground ○ ○ BR - 66
C1210 - Range/Performance: speed jump or damaged exciter ○ ○ BR - 67
C1211 No signal: air-gap error or wrong excite ○ ○ BR - 68
C1604 ECU hardware: ECU internal or valve failure ○ ○ BR - 70
C2112 Valve relay: valve relay or fuse failure ○ ○ BR - 70
C2402 Motor-Electrical: open or short to battery, motor relay, fuse or motor lock fail ○ ○ BR - 71
C1503 TCS switch failure δ ○
C1605 CAN Hardware failure δ ○ BR - 71
C1610 CAN Bus off failure δ ○ BR - 71
C1611 EMS Time-out failure δ ○ BR - 71
C1612 TCM Time-out failure δ ○ BR - 71
C1613 TCM Un-matching failure δ ○ BR - 71
C2227 Brake disc overheat δ ○
C1274 G-Sensor signal fail (only 4WD) ○ ○ BR - 72
C1275 G-Sensor open or short to ground (only 4WD) ○ ○ BR - 72
You'll need a scanner which is compatible with Hyundai's ABS system to retrieve any DTC's (Diagnostic Trouble Codes) stored in its computer. Any time the ABS light comes on, there's a DTC stored in its computer - that code will tell you where the problem exists. Then you can go from there.