I fixed a 2004 VW Touareg 3.2L V6 engine with the airbag SRS light on last night.
Trouble diagnosis:
I used Launch X431 IV Auto Scanner to read the trouble code. It showed that the seat belt switch on the right side had problem. The driver said he had changed the buckle of seat belt in the passenger position. But the trouble still happened.
I thought that there were three reasons for this trouble. (1) Launch X431 IV is not the special diagnostic tool for VW. It may send the wrong message. (2) The changed buckle of seat belt had poor quality. (3) Something wrong with harness of buckle or airbag control unit.
First, I wanted to figure out whether Launch X431 sent wrong message. I took out the plug of seat belt switch in the passenger position. Also, I took out the plug of airbag igniter. Launch X431 showed the same trouble. It meant that the diagnostic tool was ok.
Then I measured the resistance of new seat belt switch. It was also ok. I measured the old seat belt switch. And I found that they had different operational principle. The new one had good quality, but it cannot match the old one. I looked the numbers of seat belt buckle. The new one was 716857 778 E. The old one was 716 857778 B. They were different.
Why the trouble code of the old one cannot be erased? I measured the resistance of airbag switch in the diver position. It was 400Ωwhen the seat belt had not been plugged. After plugging the belt, it was 99Ω. It meant that airbag switch in the diver position had wrong resistance. So it caused the trouble code. Maybe the poor connection in the switch leaded to the wrong resistance.
Troubleshooting:
I replaced the buckle of seat belt which had the same type. The trouble was cleaned out successfully.