greg [HAWAII]
hik9sar@aloha.net
If you're talking about the OBD II reader it's really a must as there's no way to determine what "Check Engine" means. On some models, the error code(s) will appear if you toggle the ignition key 3 times. I know it doesn't work on mine (99 D). The OBD II readers are now fairly affordable and of course you can use them on any car post 1996 and go for about 120 bucks. Just my 2 cents...
greg