I get where you're coming from in that an engine workshop message doesn't seem the most obvious fault indicator for a faulty brake light switch, but this problem is ridiculously common on a mk4 and has been covered thousands of times.

It's easy to get over paranoid about it, but just sit back and be grateful that it's likely only a 10 minute fix, and perhaps actually listen to the advice given.

 

since you are a lazy git, i did a straight copy and paste from the link i provided ( next time if you can't be arsed i won't even bother to reply)

16955/P0571/001393 - Brake Light Switch (F): Implausible Signal
Possible Symptoms

• Malfunction Indicator Lamp (MIL) active
• Glow Plug Indicator Light active
• Brake Light(s) not working

Possible Causes

• Wiring and/or Connectors faulty
• Fuse(s) faulty
• Wrong Brake Light Bulb installed (21W instead of 5/21W)
• Brake Light Bulb(s) faulty
• Brake Light Switch (F) faulty

Possible Solutions

• Check Wiring or Connectors
• Check/Replace Fuse(s)
• Check/Replace Brake Light Bulb(s)
• Check/Replace Brake Switch (F)

Special Notes

• Brake Light Switches (F) have the reputation of breaking quite often.
• When found in the NAR market 2011+ (16/AJ) Jetta Sedan using PR code AW0 Version Low in addition to a BCM25/PQ25 BCM check the wiring to/from the brake light switch. Internal Ref: ST?ID=66540

 

The issue i posted above is a fault but i don't think it's what's causing the workshop message to come up on the dash, now the glowplug light is constantly flashing when am driving.

 

by now you should know where to look these codes up.... click here