My son just bought a 2001 Subaru Forrester with 177,000mi. His check engine light came on last night and the code reader indicated low catalyst efficiency. Does this mean we need to replace the catalytic converters? Could the problem be the oxygen sensors? This car has 2 converters that must be replaced together.
You need to have a good diagnostician connect a real scantool to your car and monitor your oxygen sensors and fuel trim to see if those are normal. This code can be a challenge to deal with, and the catalytic converter itself is one of the least likely culprits. If you do end up having to replace your catalytic converters, make sure to get a high quality unit that is guaranteed OBD2 compliant or else you will never get rid of that code.
Since the car is so old I’m thinking we should probably replace the oxygen sensors anyway. I may just give them a shot since they are cheaper and probably need to be replace. What do you think?
It certainly can’t hurt, as long as you don’t expect any miracles. Don’t be disappointed if you replace them and it doesn’t solve this problem.
No miracles are expected. I figure the oxygen sensors are probably due to be replaced anyway. If that fixes the problem, fine. If not then we’ll take the next step and have a mechanic do a diagnostic or just replace the converters. Thanks for your input.
One simple test (to check how well a cat.is working) is to compare the inlet and outlet temps of the cat. Tested with an hand held pyrometer the outlet should be at least 100F or 8% above the inlet. There are tests (with a 5 gas analyzer) that will give a more detailed report.
Don’t get your cat. replaced until at minimum the cat. fails the “inlet temp compared to outlet temp” test.