My car has an error code that won’t go away

John Paul, AAA Northeast's Car Doctor, answers a question from a reader who is still getting an error code despite making repairs.

Chevrolet Aveo LT Chevrolet

Q. I have a Chevy Aveo and I am having issues with the PO420 code. Both oxygen sensors were changed. The wire connections are good and I use quality gasoline. The car runs great and has 117,500 miles, but the check engine light still comes on. What is wrong? 

A. The code is looking at catalytic converter efficiency. More than likely the converter just can’t perform properly, and that is determined by the front and rear oxygen sensors. You are correct that you wouldn’t notice any difference in engine performance, but the engine is producing higher than normal vehicle emissions. When you replace the catalytic converter, buy a quality replacement. I have seen bargain converters work for a while only to have the same PO420 code come back.  


Q. I have a 1985 Chevrolet Corvette with the 4+3 transmission and 48,000 miles. I recently had both hydraulic cylinders for the clutch replaced. Now the reverse lights and the overdrive indicator in the info center do not work. Both are obviously transmission related. Any idea what the issue could be?

A. When the transmission was removed, the reverse light switch, located on the side of the transmission, needed to be disconnected. The overdrive switch is located on the shifter. I suspect that during the repair these items may have been left disconnected or perhaps even damaged. At this point go back to the shop that did the repair and have them inspect their work. 

Q. What do you think of the new Ford Bronco and the Bronco Sport? 

A. I have had the opportunity to evaluate both vehicles within 30 days of each other. Before driving them I expected to not like the Bronco Sport, because it’s based on the Ford Escape platform and I love the full-size Bronco. In reality I liked the Bronco Sport a lot. It rode well, had off-road capability, and was quite functional inside and out. The full-size Bronco was sharp looking, got plenty of attention, and is an off-road champion – but maybe because of all the hype I came away a little disappointed. The interior seemed a bit too plasticky in places, and fit and finish were average. And then there was the price. The Bronco I drove was approaching the price of the off-road capable and more luxurious Land Rover Defender. 


Q. I have a 2008 Toyota Avalon which is the best car I have ever owned. I purchased it new but the one problem that I have is the high beam bulbs have shattered or blown out every few years. My mechanic said Toyota had sent a bulletin to the dealers about the problem. It is my understanding that some 2008-2010 models have a problem with the bulb housing, not the bulbs, and that the fix is to replace the housing. The problem is Toyota doesn’t consider this a defect, and only covered the issue for the original warranty that expired nine years ago. To me it is a manufacturing or design defective, and the car should be recalled. The local dealer just shrugs and tells me it is an old car. To replace both headlight assemblies and bulbs will cost nearly $1,000.

A. As you stated, there is a technical service bulletin that describes the problem. The repair does in fact require replacing the housing and bulb. My guess is this isn’t a recall, since the low beam light will still function when the high beam light fails. At this point it couldn’t hurt to file a complaint with the National Highway Traffic Safety Administration on their website: There are aftermarket replacement parts from online companies such as RockAuto and CARiD with the parts costing much less. Since this is the best car you have ever owned and it probably has some additional life in it, spending $500 or even $1,000 on headlights to me is money well spent.


John Paul is AAA Northeast’s Car Doctor. He has over 40 years of experience in the automotive business and is an ASE-certified master technician. E-mail your car question to [email protected] Listen to Car Doctor on the radio at 10 a.m. every Saturday on 104.9 FM or online at


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