VR Holden Commodore problems?

By drain pipes I presume you are meaning the condensation drain for the heater box. You need the car on a hoist or stands to get at it as it drains underneath the car. As for the engine check light you need to check the codes in the ecu and be able to decipher them. It may be worth your while to pay a dealer or mechanic to pull the codes out of the ecu and tell you what they mean. then you will know where to start. Most vehicles (Commodores included) have known issues. It may very well be something simple.