The emissions warning light is on

Blocked or defective cat or the exhaust sender unit is faulty

have the fault codes read
use the scan tool to reset the ecm

thermostat

On vehicles equipped with antilock brakes (ABS), a second warning light is provided to warn if a problem occurs within the ABS system. The ABS lamp comes on when the ignition is turned on for a bulb check, then goes out after the engine starts. If the ABS warning light remains on or comes on while driving, it indicates a fault has occurred in the ABS system.

What happens next depends on the nature of the fault. On most applications, the ABS system disables itself if the ABS warning light comes on and remains on.

P0496 is not alisted code.
P0455 - Evaporative Emission Control System Leak Detected Gross Leak (fuel vapors)
Symptoms - Engine Light ON (or Service Engine Soon Warning Light)
- Possible a noticeable fuel odor caused by the release of fuel vapors Possible causes - Missing or loose fuel cap
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap
- EVAP canister or fuel tank leaks
- EVAP system hose leaking
- Fuel tank leaking

Hello
There are a number of things that casue this fault code, here is some info on what the problem might be.

440 - Evaporative Emission Control System Malfunction
Symptoms - Engine Light ON (or Service Engine Soon Warning Light)
- Possible a noticeable fuel odor caused by the release of fuel vapors.
Possible causes - Missing or loose fuel cap (most common)
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap
- EVAP canister or fuel tank leaks
- EVAP system hose leaking
- Fuel tank leaking

CODE PO441 - EVAPORATIVE EMISSION EVAP SYSTEM INCORRECT PURGE FLOW. WHAT IS HAPPENING THE PCM DETECTED THE PURGE SOLENOID VALVE REMAIN OPEN DURING THE EVAP MONITOR FLOW TEST.

I suspect there is still a small leak somewhere, but that could be hard to find. I don't know where you live, but if you have to have your vehicle smog checked, it will not pass in this condition. It doesn't matter if the light is is disconnected, the computer will still show the error code. You are probably not doing damage to the car. There are shops that have methods to detect the leak.

Have a shop scan for the codes this will point you in the right direction of what is wrong.They usually do it for free.It only takes ten minutes.

I bought a 2000 polo 1.4 yesterday after having an MOT. The warning lamp came on today but the car is running fine. Whether its the Lambda sensor or just the light itself is a common fault, I think garages turn off the lights to get it through the MOT then they come on again in a day or two!