Please help, I’m try to program my keyless entry into my 2003 hyundai elantra gls 4doors manually, I searched all over the net on how to locate the ETACS “on/set” switch but I failed. My ETACS module doesn’t have that switch.

SOURCE: keyless entry programming instructions

can you check with dealer

SOURCE: Program factory remote keyless entry: 2003 Hyundai XG350

The procedures you list require the Hyundai Keyless Remote programming module, which you don't have. This module is proprietary - only Hyundai Dealerships have it. There is a 10 pin connector under the dash (next to the DLC - Data Link Connector) which is used to connect the Keyless Remote Programming Module. This module has two switch positions "Ready" and "SAVE". When the switch is place in the 'SAVE" position, that's when the keyless remotes are activated to send their 'codes' to the Electronic Time and Control System (ETACS). The module's switch is then set to "Ready" and the remote is tested to see if it works properly.

SOURCE: Program factory remote keyless entry 2003 Hyundai XG350

I've informed you of what you need to do. Take the veh into a Hyundai Service Center - let them program the remotes.

SOURCE: program factory remote keyless entry for 2003 Hyundai XG350

This bulletin supersedes TSB# 02-90-001.
DESCRIPTION: The security system keyless adapter cable (SPX/Kent-Moore P/N 09900-21300) is a special service tool (SST) that is used for programming new keyless entry remote transmitters to the factory security systems. The keyless adapter is used in conjunction with the Hi-Scan Pro (with Hi-Scan SOL Pro Software Version 09-29-03
or newer) and Data Link Connector (DLC) Cable. SERVICE INFORMATION: The keyless adapter cable can be used on the following vehicles:

• 2001 - 2004 MY Elantra
• 2001 - 2004 MY Santa Fe
• 2002 - 2004 MY Sonata
• 2001 - 2004 MY XG300/350

• The 2003 - 2004 MY Tiburon does not need the Keyless Adapter Cable to add keyless entry remotes to the factory security system. Instead, the Hi-Scan Pro connects to the vehicle using only the DLC cable. See page BE-60 in the 2004 MY Tiburon Shop Manual for the latest instructions.
• The most current Keyless Adapter Cable Instructions are available in the following shop manuals:

1. Connect the keyless adapter cable to the Hi-Scan Pro DLC cable.
2. Plug the keyless adapter into the vehicle's 10-pin multi-purpose connector located behind the driver's side lower instrument panel (next to the DLC). NOTE Sample vehicle shown is the Santa Fe.
   
3. Turn the Hi-Scan Pro ON
   and press ENTER
   . NOTE "Release date 29. Sep. 2003" OR LATER
   must appear on this screen. To update your SOL card with the latest software go to www.hmaservice.com and refer to TSB 00-00-001.
   
4. Select option "HYUNDAI VEHICLE DIAGNOSIS"
   and press ENTER
   .
5. Select vehicle model and press ENTER
   .
6. Select option "TRANSMITTER CODE SAVING"
   and press ENTER
   .
7. Ensure that the key has been removed from the ignition cylinder before proceeding.
8. Follow the steps noted on the Hi-Scan Pro screen to program the remote(s). NOTE The factory security system can only be programmed to accept two remote transmitters and MUST be programmed for both remote transmitters at the same time.
   
9. Press ESC
   on the Hi-Scan Pro and verify that the remote(s) are functioning properly.
10. Turn the Hi-Scan Pro OFF
    and disconnect the adapter cable from the multi-purpose connector.

SOURCE: 2003 Hyundai Elantra GLS. Check engine light, code PO133

Did you use a aftermarket O2 sensor or a genuine Hyundai one? If it's an aftermarket one it may be bad or not as good as the OEM one. See here for more details and other potential causes: P0133