Join the community and post your question. Use our Ask-A-Tech for free now! ASE experts standing by.

Forum > Failed Smog Test > Question

My Lexus LS 400 Did Not Pass the Emissions Test

I am wondering if an exhaust leak can cause my Lexus LS 400 to fail the 25mph emissions test. It failed by 25 ppm on the NO portion of the smog check. Thank you.
Answer:

Assuming the exhaust leak is located between the exhaust manifold and the catalytic converter, you will need to have it repaired before your Lexus LS 400 can pass the smog check. The exhaust leak can absolutely cause an emissions failure. The fault here is two fold, in that, it posses a "functional" failure if the leak is loud enough to be heard by the smog technician, and a high emissions reading (as your vehicle has experienced) as well. Having an exhaust leak such as this will disrupt the engine's air/fuel ratio (as it exits the engine) which is necessary for proper catalytic converter operation, typically causing high NO. The exhaust leak may also cause improper oxygen sensor readings, compounding the high emissions problem. Without correct oxygen sensor readings, the engine emission computer, can not determine how much fuel to the air/fuel mixture. Incorrect air/fuel ratio (14.7:1 is optimal), will cause force the engine to burn fuel inefficiently. posted by SmogTips Support

Related Lexus LS400 questions and answers you might find useful:

Where is EVAP Canister Located on Lexus LS400 by Sheri

Lexus LS400 Failed EVAP the smog check EVAP Test by Ron

1991 Lexus LS400 failed test smog test for high HC. by krk

View SmogTips.com in: Desktop / Mobile