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Consumer Assistance

Because Battery was Changed Car Cannot be Smogged

I took my car to a smog check station and was asked if the battery had been changed. It had been awhile back. I was told it could not pass a smog test until the computer was reset; at a cost of $135.00.This car has always past before. What difference would this make if they are sticking the tester in the exhaust pipe? It would either come out clean or not clean. The other option was to drive the car a lot before bringing it back to get smogged. This car is driven very little. It is a 2002 model with less than 60,000 miles.


Replacing the battery or even simply disconnected the battery on a vehicle will cause the engine control unit (ECU) to reset and clear all the emission monitors (and trouble codes; if any existed). Emission monitors are needed to be READY or COMPLETE in order for the vehicle to pass the smog check.

Completing or making "Ready" the emission monitors requires driving a car through a specific driving pattern. Emission monitors are internal self-tests which the ECU performs to ensure a vehicle is not polluting and is running efficiently. The entire process of self-testing various emission control systems is called a Drive Cycle.

It is recommend to drive a vehicle 200-300 miles and over the course of a few days in both city and highway traffic conditions in order to make the emission monitors "ready".

posted by SmogTips Support 06-10-2016 01:21 PM

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