DIAGNOSE – EXCESSIVE ODOR EMITTED FROM TAIL PIPE (Rotten Egg Smell)

By Carl O’Reilly

SYMPTOM SUMMARY
There is excessive odor emitted from the tail pipe. The odor may smell like “rotten eggs”. If there is exhaust smoke present, refer to the “Excessive Smoke From Tail Pipe” symptom on this website. If the vehicle has failed an emissions test, refer to the “Emissions Test Failure” symptom also on this website.

USUAL CAUSE
This symptom can be caused by an excessively rich air/fuel mixture. If the vehicle only exhibits this condition after severely loading the engine, as with mountainous driving, the condition may be normal. If the “Check Engine” or “Service Engine Soon Light” is on, refer to that symptom for diagnosis.

DIAGNOSIS
An exhaust odor that smells like rotten eggs is the result of a rich air/fuel mixture. This condition may be the normal result of placing a heavy load on the engine, as with pulling a trailer or heavy grade. The catalytic converter is responsible for reducing the Carbon Monoxide and Hydrocarbon levels in the exhaust. When the air/fuel mixture is too rich, the catalyst cannot convert all of the additional fuel in the exhaust. The result is a foul odor that is often asscociated with rotten eggs. If the vehicle only emits this odor under the above conditions, the symptom is probably normal. However, if the vehicle also has a running problem, engine warning light on, or emits the odor under all operating conditions, further diagnosis should be performed.