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P0131 and p0171

i have 2001 volvo s40. today, suddenly, Check Engine Light on and i have it diagnosed and there are P0131 and P0171.

i searched web about error code: p0171 is too much air and not enough fuel. P0131 O2 sensor circuit - low voltage.

are they because: i use K&N air filter? (but i diagnosed after i changed to regular air filter) - this is for P0171.

should i changed O2 sensor for P0131 ?

appreciate any insights.

No. Don’t change the O2 sensor. Clean the MAF sensor. That K&N filter probably contaminated the MAF sensor and after changing the filter the MAF sensor is still contaminated and that’s what’s causing the codes.

Purchase some MAF sensor cleaner, remove the MAF sensor and clean the MAF sensor hot wire. BUT DON’T TOUCH IT! Reinstall the MAF sensor, clear the codes and see if the CEL comes back on.

And throw that K&N filter in the garbage.


Then change the oxygen sensor…

I’m not a fan of K and N filters either. Since the car is 10 years old not a chance of a vacuum line unplugged, cracked, etc. during this air filter swap is it?

An air leak can cause codes like this. Not saying this is the cause; just something for consideration.

Just a thought on this issue. The P0171 code may be a result of the other code issue. By finding the trouble that is causing the P0131 code the other may go away also. Check for a bad connection to the O2 sensor.

thanks much, all.

i will do that.

It worked for a while. Last 2-3 weeks when my wife used the car, Check Engine Lights came on and it “hesitated”, then at around 3-3:30 pm ( the hottest part of the day in charlotte, nc), it stopped.

By the time, i arrived at the scene about 1 hour later, it started again. everything seems normal. It happened twice and at the same time of the day. I just re-cleaned the MAF sensor after the first time it happened.

The error codes: P0171, P0301 ( cylinder 1 misfire ), and P0304 ( cylinder 2 misfire) . I checked the spark plugs on plug no. 1 and no. 2 and they seem to be similar condition.

is it time to change the O2 sensor? BTW what is “vacuum line” ? is the line/hose that follows after the MAF sensor ?

Thanks much for ideas/suggestions.

BTW, I throw away the K&N filter and bought air filter from volvo dealer.

Age can put the O2 sensor in the replace timeframe. There can be other issues as noted above but O2 sensors do die and they are not a big cost. Misfires can be poor wires(have they been replaced in the last 25k) or bad plugs or bad injectors. At this point I would look at the upstream O2 sensor.

tx much. local pepboys mechanics suggested that it might be ignition coil. tough one is that it is hard for me to reproduce the incidents.