WARNING LIGHT IS CONSTANTLY ON

You will need a scan tool that works on that BMW to clear any warning lights such as a check engine light. Unless you have resolved the problem/ fault that has caused the warning light you are wasting your time clearing it as an unresolved fault that has not been fixed will, once you drive the car again, generate the check engine light again together with a bunch of fault codes that can be read by the scan tool.

Looks like you have a few issues there.

1. The battery warning. This is indicative of a weak battery and if your battery is 3 years old or more I would replace it.

2. If you have a weak battery this can trigger other warning lights in the vehicle, typically the ABS warning but sometimes other warning lights as well depending on the electronic features in the car. If you replace the battery this should correct the battery warning and most likely the ABS warning if both of these warnings appeared at the same time.
Normally, once the ABS warning is displayed the anti lock braking system(ABS) will be shut down. Whilst your braking will be normal, if you brake too hard and lock up your wheels on a slippery road there is no ABS assist to prevent the brake lock up which you have when the system is working.

3. If the alternator on the engine is not generating sufficient power and thus not charging the battery at all, or very little, you will likely get a battery warning light. I don't know if your 1999 vehicle has a warning light to indicate a faulty alternator or not.

4. Check Engine Light.
You suggested the CE warning has been showing up for a few days and before the battery and ABS warnings popped up.
The CE warning can be caused by dozens of different engine issues.
The vehicle needs to be scanned with the appropriate scan tool to see what fault codes the onboard computer is generating because if you have a CE warning light there will be fault codes generated 99% of the time.

Once these fault codes have been pulled the mechanic can start to diagnose the cause of the problem or problems. Each engine fault code your car's computer is generating can be caused by different types of problems so it is important that they diagnose the issues correctly. Otherwise your Check Engine light will remain on as long as the causes are not identified and fixed.

the transmission warning light is an indication of a fault in the transmission which you apparently ignored. You were supposed to have that fault codes read immediately the light came on as that is when the repair will be at the cheapest. have the codes read now to determine what is wrong

Your vehicle may have an "oil level" sensor built into the oil pan. If so, and the sensor is bad, the dash will constantly tell you that the engine needs more oil even if it does not. Checking the oil with the dipstick, a minute after the engine has been turned off on level ground is always the best way to check your oil. Try scanning the vehicles computer systems to see if there are any fault codes. The warning light may also be on a timer that just needs to be reset. The "Check Oil" light should be separate from the engine oil pressure warning light. As long as the engine oil pressure light stays off, you should be ok. Checking the oil pressure with a manual gauge would be a good idea as well.

Haynes manuals are ok but leave a lot out of them like the fault codes. Clymer Manuals are a lot better in technical advise than any other manual. I believe they will have how to find the fault codes on your bike. Hope this helps!

Run fault codes to find out what put the engine light on. Replace or repair asap as it is telling you that something serious has happened to the engine management systems. Check oil level and coolant level at the radiator. To ignore a warning light is an invitation to expensive disaster.

Hello and welcome to fixya.com
turned on by the systems computer it is to alert you to the fact that the computer module has detected a fault in the systems operation, this can be the engine, the emissions system or the transmission. What must be done now is to have the system scanned for fault codes, these are called OBD2 fault codes, then diagnostics are performed to determine the cause of the fault codes and repair made based on the diagnostics performed.

This warning means that a fault has occurred that would have disabled the car in older models, the computer control has worked around the fault to avoid stranding you with a non operational car. You need to see a dealer or a well equipped shop and have the computer scanned for the fault code or codes that are stored when this happens. The engineers who design cars and trucks call this "Failure Mode Strategy"

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!