CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Check Engine Light - Subaru

Our 2002 Subaru wagon’s check engine light keeps turning off & on. The code indicates a problem w/ the catalytic converter. Our mechanic suggested trying super gas, which doesn’t seemed to have made a difference in the light coming on. Anyone with a similar experience or suggestion?

There should be a specific code or codes related to your light. There are a number of possible codes that might relate to the converter. The code should be in the format [P1234]. Post that information back here.

How many miles on your car and what date was it sold? If it is a pollution control issue it may be covered under the warranty which is likely longer on the pollution control parts, than the rest of the car.

In addition to Mr. Meehan’s questions, I want to ask about some of the other information that you neglected to tell us:

Odometer mileage?
Engine type?
Maintenance as per mfr’s schedule?

The question regarding engine type is relevant because if you have the 3.0 H-6 engine, premium gas is recommended for that engine, and I can tell you from experience that using it consistently is important for maintaining performance.

On the other hand, if you have the 2.5 liter 4-cylinder engine, that engine will run very nicely on a steady diet of regular gas and using premium gas will not improve anything. Truthfully, if your mechanic is telling you that using premium gas in a “regular gas engine” will cure this problem, then I question the mechanic’s competence.

I asked about maintenance because if you have not kept up diligently with maintenance, that could present other relevant issues.

If you fill in the blanks for us, we can likely be more specific with suggestions.

Thanks for your reply. The code is P0420 “Cat. Eff. Low Bank #1” It has around 117 K miles. We bought it in 2002 - my husband just told me it’s actually a 2000, not 2002 as I originally posted. It had very low miles when we got it.

117 K. 4 cylinder. We do pretty well with maintenance. I gave the incorrect year - it’s actually a 2000. So far, the super gas isn’t improving milage & hasn’t stopped the check engine light from turning on periodically, though it shuts off on its own, too.

Codes simply point you in the general direction and then the diagnostic work begins.

In your last post you now mention that this “super gas” is not improving mileage, which is something you did not mention previously.

So does this mean the engine is running poorly, idling somewhat rough, etc?
How long since the spark plugs were even changed?

The Subaru 4-cylinder engine does not require premium gas and will not run one iota better with premium gas. So, as I said, I seriously question the competence/expertise of a mechanic who suggests that this will cure your engine problems.

Regarding maintenance, you told us, “We do pretty well with maintenance”, and unfortunately, that type of general statement is not helpful to us. I strongly suggest that you take out the booklet entitled Subaru Warranty and Maintenance Supplement, and refer to the 90k mile service. If you have not had ALL of the maintenance procedures listed for the 90k service performed, you need to do that as a first step, as I strongly suspect that this problem is the result of lax maintenance. After doing all of the required maintenance, the problem may resolve itself, but if it doesn’t, a competent mechanic will be better able to diagnose and fix the problem.

Also, your engine needs to have the timing belt replaced by 105,000 miles or 7 years, whichever comes first. Unless you know for sure that this vital procedure has been done already, I urge you to have it done a.s.a.p., as it is seriously overdue. When that belt snaps (without warning, I might add), valves and pistons will collide, causing about $2,000 worth of damage to the engine. The water pump, serpentine belt, and belt tensioners should be replaced at the same time as the timing belt.

All of the necessary maintenance (90k service + timing belt and related components) will likely cost you about $800-$1300 in total, depending upon where these services are done. However, if you expect to keep this car for more than a few weeks, they need to be done. Maintenance is not cheap, but it is far cheaper in the long run than the repairs that will result from a lack of maintenance.