SES Light?
Thread Starter
Teching In
Joined: Apr 2005
Posts: 37
Likes: 0
From: Fort Worth, TEXAS
SES Light? I have a 97 Mazda 626 with 98,000 miles on it. the SES light came on last friday and i took it to autozone to check the code. He used the actron code reader and the code was P0240, the catalyst system efficiency for bank 1 is below threshold for the current engine operating conditions. The guy at autozone said i might have a vacuum leak or and oil leak. He confused me. Does any one have any suggestions on what it could be? Thanks.
TECH Veteran
Joined: Dec 2004
Posts: 4,012
Likes: 1
From: Beaumont, TX
Probably O2 sensor or bad cat 
Correct code for that is P0420, btw.
https://ls1tech.com/forums/pcm-diagnostics-tuning/44855-p0420-cat-o2-sensor-gone-bad.html
https://ls1tech.com/forums/pcm-diagnostics-tuning/41927-code-p0420-keeps-coming-up-what.html
Correct code for that is P0420, btw.https://ls1tech.com/forums/pcm-diagnostics-tuning/44855-p0420-cat-o2-sensor-gone-bad.html
https://ls1tech.com/forums/pcm-diagnostics-tuning/41927-code-p0420-keeps-coming-up-what.html
with a po420 if you dont have any o2 codes that accompany it,which if you did you would diagnose them first,from my experiance your looking at a converter effiency problem.The computer moniters the front and rear o2s.Also make sure theres no exhaust leaks,probably gonna have to replace cat!
