i was suppose to post this a while ago. my brothers 1997 mazda 626 engine light was on for a while and no one that i knew could find out what was wrong until we too it for emissions. and the diagnostic report said

MIL engine off: PASS
MIL engine on: FAIL
DLC rampering: PASS
OBDII Communication: PASS
MIL Command Status: FAIL
Fault Codes: P0400 EGR Flow Malfunction
P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)

can any one help me with this and how to get it to pass emissions

 

replace the cat........as for the egr......sounds like it has a lift sensor, check the vacuum soleniod which supplies vacuum to the egr. also make sure the egr isnt clogged to where it cannot open. damnit and also check the vacuum lines going from the intake manifold to the egr vacuum solenoid and to the egr valve.

 

A quick check for the EGR valve is to push the diaphragm in while the engine is idling. If the engine starts to run bad, then the EGR valve is working properly and your problem is probably caused by the EGR valve not bieng given vacuum to open.