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Check engine light

My dad has a 96 buick century with the “service engine soon” light on. A computer diagnosis said P0401. Said egr valve or oxygen sensors. The guy said it’s probably the egr valve. I replaced it and cleaned the old carbon out but the light is still on. I noticed a cheap hose of some kind, maybe tin or alunimum, that goes from the egr valve to somewhere. Probably the original hose. Could that have enough carbon in it to affect everything, or should I replace the oxygen sensors? Since there are two, which would be the most logical to replace 1st? I don’t want to replace both if I don’t have to. I never replaced anything like that, it it something that isn’t too difficult, or have a professional do it? Thanks.

“P0401 - Exhaust Gas Recirculation Insufficient Flow Detected”

To properly clean out the EGR, not only the valve itself but all the lines and hoses running to it and from it. If this is the 4.3L V-6, the exhaust gases flow through the cylinder head and the intake manifold to the EGR. Then is metered to the intake plenum.

However, this may also be a code for a bad flow sensor. If the EGR paths are clear, and the EGR is functioning normally, there may be a bad sensor.

It is a v-6, although what size I don’t know. I think I’ll replace the hose I mentioned that goes from the egr to ? That looks like an easy job, 5 minutes.

Like I said, the computer readout said egr or oxygen sensor, but the guy said there were 2 of them on this car. Is the oxygen sensor the “flow sensor” you mentioned, or something else? I’m thinking you’re talking about a mass air flow sensor, (I have a problem with my maf sensor I need to deal with soon.) I’m not up to all these computer cars or wouldn’t need the help. Since the egr valve is new, I’ll replace any hoses I see and see what happens. Dad may have to take it in and pay for professional help. Thanks for everything though, I appreciate it. Downright neighborly, in fact.

If you were to go to and register, you could get a little information on the Buick. Then, you could click on this link which would take you to the wiring diagrams (which take about 5 minuets to load). Fig. 79 is for your 3.1L engine, and shows that egr flow is controlled by the Digital EGR Assembly, which is controlled by the engine computer.
If you had a repair manual, such as Haynes, or Chilton’s, you could get the instructions on checking the digital egr assembly. This may be beyond your abilities, so, the mechanic will have to take over the troubleshooting. It’s not a piece of cake even for experienced mechanics.