I have a '99 legacy with roughly 112,500 miles. Back in October, the ‘check engine’ light came on for the first time since I’ve owned the car (just over a year). Soon thereafter, I brought the car into my mechanic, who found a P0420 code. He told me that he frequently often sees Subarus with CELs on in early winter as gas stations switch from their summer to their winter fuel. He cleared the code, asked me to keep an eye on it, and let him know if it came on again.
Earlier this month, the light came on again, and sure enough, it was a P0420. He suggested a few less expensive treatments before replacing the catalytic converter, including going up temporarily to a higher octane fuel. He also mentioned that the cats on older Subarus are sensitive to fuel that contains ethanol, and I could try something like Lucas Ethanol Fuel Conditioner.
The trouble is that, when I recently looked at the car’s records, I saw that a new catalytic converter was installed at 95,000 miles. Could it be that the cat is failing after less than 20K? Are there other things I should look at before putting in a brand new one?
Your thoughts would be most appreciated!