The red LED light that is built into the car only tests the diagnostic module.
The diagnostic module receives information from four other modules-- LH-SFI module (fuel injection), EZL-AKR module (ignition timing), EA module (engine accelerator a/k/a electronic throttle actuator ("ETA")), and the ABS/ASR module.
A code 6 on the diagnostic module is telling you there is a problem with your EA (ETA). You will need to test that specific module (EA module) by building the DIY tester and checking pin 7 of the 38-pin canon plug connector next to where the LED light is. The LED module will not check this pin. Here are the codes for the ETA from J. Forgione's excellent website:
http://www.k6jrf.com/MB_EA.html
The problem could be something as simple as changing the neutral safety switch or stop lamp switch behind the brake pedal. I'm curious, how much did it cost to replace your ETA?