Recently obtained a 97 RS and have the "Service Engine Soon" light giving me a code reading of 1406. I've read the manual and 1406 does not match format of the OBD codes.

Any ideas would be greatly appreciated.

 

Have you been looking up the code for your specific car only, or just in general?
Because on some other GM models it means an "EGR Valve pintle position circuit failure."
Could be your EGR valve is carboned up, a good place to start anyway.

 

For my car. What confounds me is that according to the manual (for my '97 RS) all the OBD I codes are two numerical digits, and the OBD II codes all begin with P followed by three numerical digits.

I'll do some research on the EGR valve, though. Thanks much!