2001 Jetta Check Engine Light

I replaced my Catalytic Converter with an after market part at a shop. A couple days later the check engine light came on again. The shop told me that the problem was that I need a new INternal Control Module Processor but I would have to take it to the dealer for that.

The dealer said it was just a ground wire that they fixed. 2 days later the Check Engine light is on again. The dealer says that the after market Cat isn’t efficient enough and I need t replace it with a VW cat. I don’t want to pay for their experiments. What should I do? Is it really an OEM to after market problem, or is it the Internal Control Module?

Take a look at your paper work. Did either mechanic write down the trouble code/s they came up with? If so post them here.

If not call around to some auto parts stores such as Autozone, and find one that will pull the trouble code/s.
They will do this for free.

Ignore anything they tell you except for the trouble codes.

Post those codes here.

Properly fixing your car is all about the trouble codes & finding mechanic that will follow the troubleshooting flow chart for the code/s

These are the codes after the Cat was replaced

P0606 Internal Control Module Processor Fault
P0420 Catalyst Efficiency Below Threshold
P0300 Random Multiple Misfire
P0303 Cylinder #3 Misfire

Well, I did a quick google search on “PO606 + Volkswagon” & found that it can be caused by a weak battery. Has your battery been load tested?

The PO420 would be ignored until the miss fire codes were corrected.

Odds are PO420 would go away once the missfire problem was fixed.