Car Talk: No need to be skeptical about updated emissions tests


By Ray Magliozzi - Car Talk



Dear Car Talk:

You recently had a column about roadside emission test stations. I live in an area where our cars are required to be tested every two years to renew license plates. The testing stations here are mostly along interstate highways, and I drive by them frequently. I seriously doubt with thousands of cars going by and with the wind blowing that they are able to test emissions and somehow determine which car the exhaust came from.

I recently received my notice and am required to take my car to a testing facility and pay $25 for the privilege. The whole deal is nothing more than a revenue source for the state and does nothing to take polluters off the road. —Ed

As I would often say to my brother when he said something off the wall, “Au contraire, piston puss.” I can tell you’re a skeptic, Ed. But I think your information is a little bit out of date.

You’re thinking of the old days when your emissions were checked by sticking a probe up the tailpipe. Kind of like taking a kid’s temperature. The mechanic would insert a metal probe with a hose on it in the tailpipe, and it would suck exhaust gasses into the analyzer. That would tell us how much carbon monoxide and unburned hydrocarbons you were putting out.

But that’s not how it’s done anymore. Now, the vast majority of emissions tests are done by tapping into the car’s computer directly. We have a device that we plug into the car’s diagnostic port, and it gives us readings from the car’s own internal sensors. It tells us, for instance, the composition of the exhaust before it goes through your catalytic converter, and after it goes through. And from that, we can tell whether the converter is doing its job.

We can also tell if, for instance, there are too many unburned hydrocarbons going into your converter, which means the problem is in the engine, not the emissions equipment. And because it’s all measured deep inside the exhaust system, nothing nearby will affect the reading, not a car idling in the next bay, not a passing FedEx truck, not even my brother puffing on one of his 25-cent stogies.

Now, there may still be places in the country where they use a probe. Emissions testing requirements are determined by the states, in order to meet the Environmental Protection Agency’s clean air rules and collect their fair share of federal highway funds. But since the computer diagnostic method is quicker, easier, more accurate and provides more useful diagnostic information, I’d be surprised if there are many emissions probes still being used out there.

So we can accurately determine whether individual cars are polluting more than they should. That means we can require that those cars be fixed. Sometimes, those fixes are covered by warranty, since the feds mandate that certain emissions equipment is guaranteed for eight years or 80,000 miles. California requirements are even more pro-consumer.

And fixing those cars really does make the air cleaner for us all to breathe. That means less asthma, less lung disease and less soot despoiling your pristine vinyl siding. And sure, it also means an extra $25 for the repair shop in your area. But we don’t make any money on those emissions inspections, Ed. It’s those new catalytic converters we clean up on.

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By Ray Magliozzi

Car Talk

Got a question about cars? Write to Car Talk write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.

Got a question about cars? Write to Car Talk write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.

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