Assuming the exhaust leak is located between the exhaust manifold and catalytic converter, it will need to be repaired before your Honda Civic can pass the smog check. The fault here is twofold, in that it posses a visual "defective" failure and more then likely a high emissions failure 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. 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.
If however the exhaust leak is after the catalytic converter and before the muffler, the only problem this may cause is dilution. The exhaust stream can be diluted to the point the smog machine will not allow the smog technician to conduct the smog check. Smog machines are calibrated in California (every three days) and are designed not to allow the testing of vehicles which emit oxygen levels exceeding the smog machines preset limits. If the exhaust leak is large enough to where air would be vacuumed into your Honda Civic's exhaust stream, the test results would be incorrect, and the smog machine may not even allow the smog inspection to begin or continue.
posted by SmogTips Support
