has codes P1500 & P0121

P1500 – Vehicle Speed Sensor (VSS)

P0121 – Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance Problem

Try erasing the code

I'm pretty sure he/they would have tried that already.

The question was why are these codes coming up after the above work
was done...

Yes, I just joined today searching on the P1500 code which the borrowed OBD2 reader from O'Reilly says is a Fuel Pump Relay Electrical Circuit Malfunction. Odd thing is, that to fix another problem I was having with multiple short to ground codes (all four fuel injectors and more), my friend who works cars on the side had found a bulletin suggesting a later manufactured fuel pump relay would resolve the problem. Well, I replaced it, and the P1500 is a brand new code now, and the short to grounds still did reoccur, though after a reset early this week, those codes didn't return but the P1500 is still there; in fact, you clear all codes, and it come up immediately again after clearing codes every time. Did I just get a bad relay? I'm doubtful now by reading the first person's experience. I'm tempted now to just pay the $75 to see what the VW dealer has to say about it.

When I looked and compared the female side for the fuel pump relay pin numbers to the male pin numbers on the relay, I became suspicious of the one I got from BAP imports as OEM being a problem, but I compared it to what the dealer part is and it's exactly the same; now just today my vehicle stalled on me and is not starting back up as if there's no fuel pressure; so I'm looking into it tonight to see if it's actually the fuel pump itself that went out. This P1500 problem does not have an easy answer I can find yet!

Finally an answer! Not what you'll want to hear (nor did I), but I took the chance and bought the dealer fuel pump relay (made in Hungary) for $60, and that did the trick, so the made in China part I had from BAP Imports wasn't made quite right enough for the 2001 VW Cabrio computer to like it. As much as I'd like to tell them their part sucks, no way I can get that money back now, just can keep it as a spare after emissions is cleared. Looks like P1500 is finally gone now and should stay gone, and as for my vehicle stalling tonight, it amounted to a vacuum system / MAF sensor issue. I took some MAF cleaner to it and I'm back in business; next, emissions testing.

Glad to hear all is well, quintus.