Suzuki Repair: service endine soon lite, oxygen sensors, solenoid valve

Question
My service engine soo lite came on and is still on in my 1996 sidekick 2-d 2 wheel drive 1.6 engine 75000 miles
  Had egr valve,by-pass valve replaced,lines blown out twice.
egr solenoid valve and manifold pressure valves checked good.
 Suzuki dealer gave me the following reading p135 and po400 I replaced 2  oxygen sensors.
Dont know what else to do,
 Help Please Mel

Answer
Ask the dealer for an estimate to SOLVE the problem.  Enter into a "contract" to diagnose the cause of the problem, then have them repair it with the written understanding that all of it is to SOLVE the check engine light problem.  After all, if they are in fact skilled and highly trained professionals, this should be easy.