Code 21 But No Misfire

[sonnyQ]

I have the annoying TCS/Slip/Engine light coming on every now and again (R34GTT), and staying on until I switch the car off. Sometimes all 3 lights will be on, sometimes only TCS and Slip. Happened at start up the other day, and has also come on after 5 mins driving. Doesn't really seem to be rhyme or reason to it..

Is returning Code/error 21 when I do the paper clip bridge thing, however I have no misfire nor rough idle and the car seems to be running completely fine apart from the occasional small pop when shifting.

My question - is Code 21 definitely failing coil packs? Pretty sure they are original (90 on the clock), so they are probably due for a change anyway, but I want to rule out any other potential probs.

[sonnyQ]

cmon guys, is it possible for the code to be returned and for it to be something other than coil packs?

[Got a Pulsar]

I believe code 21 can also be the CAS.