2006 Honda Civic LX

My car is consuming a lot of oil. Requires adding oil between oil changes. No leaks anywhere. Now mechanic says my catalytic converter needs to be replaced for $1,000. I have 96,000 miles (I drive a lot of highway to and from work each day).

How much oil? 1 qt/500 miles, 1qt/1000 miles, 1 qt/2000 miles, etc. Why does the mechanic think the cat needs to be replaced? Dealership or independent mechanic? Has the Civic always used oil, or is it something recent?

Has the PCV valve ever been replaced? A bad one can cause an increase in oil consumption. It’s only a couple of dollars for a new one.

Ed B.

I drive a little over 500 miles per week. Every 2 weeks I am needing to check/add oil. Anywhere from 1/2 quart to 3 quarts (and the car only holds a little over 3 quarts). My engine light came on while driving to work one day, so I took it right to the Honda dealership. They said the code was reading that I needed a new cat converter. They said I didn’t need it right that momemt, but gave me a friendly estimate of $1,000 for them to do it.

I have never replaced the PCV valve, so I will check into that. Also I had heard that the converter is a symptom of something else, not the cause of the problem. My gas mileage has decreased from averaging 38 miles per gallon to 34 miles per gallon recently. I know I shouldn’t complain about that kind of gas mileag, but it is a fact.

Based on your description of the amount of oil you’re burning, it sounds like an average of about a quart every 500-600 miles. That’s enough to cause problems.

Prolonged oil burning can coat not only the catalyst inside the converter, rendering the converter unable to operate effectively, but also the oxygen sensors, generally the upstream one first. What I’d suggest is first having the oxygen sensor outputs compared on a scope. If the upstream sensors redaing are normal but the downstream is showing little change, that’ll confirm a bad converter. If one of the oxygen sensor readings is not normal, the tech will see that on the scope and go there first.

Have this done at an independant shop. If it turns out to be a bad converter, they can save you a bunch over the dealer by using a direct-fit aftermarket converter.

I agree with checking the PCV first. No smoke …no leaks …the stuff has to be being burned and relatively cleanly. It can poison your cat. Rare on a domestic …but not so rare on a Honda. Honda’s are great until they need repair. The parts (like this one that may look nothing like any other converter out there) are frequently very high priced.

You might benefit from an Auto-Rx treatment if the PCV appears to be in good condition (you’ll replace it and either will or will not see the oil consumption retreat). It will assure that any coking in the ring packs is cleaned out.

As was described the cat efficiency test looks for a cycling of the front O2 sensor between rich and lean …while the downstream should not see the variation (as much). That catalyst is either soaking up or releasing O2 in a “quench and purge” manner as the incoming exhaust either has excess oxygen or excess hydrocarbons. When the rear sensor sees the same reading, with only a delay, the cat is shot. The PCM keeps count of how many times this occurs (at some point you’ll have lean conditions across both if there’s no fuel scheduled in the particular strategy of your engine for example while coasting warm). The closer the count is to zero …the higher the cat efficiency. The more events …the lower the efficiency.