steveyen: I took my Maxima on a out-of-the-state journey and through some very rough Lagos roads ( Ajao estate bad roads, Barracks estate, ogudu terrible roads). After a couple of days I suddenly noticed ' Service engine soon' showing on the dashboard.
I did a scan on the car and got the following error codes:
p0420 - Catalyst System Efficiency Below Threshold (Bank 1)
p0328 - Knock Sensor Circuit High Input
Please what could these do to the engine? What is the implication of driving the car with these codes still on? How can these be fixed?
I also noticed the car makes a louder/deeper sound than before when revved. This happens after the codes now when I accelerates i do hear a more deep/loud sound.
Kindly help your inputs will be appreciated.

GAZZUZZ: You have a leaking exhaust and a faulty knock sensor or disconnected socket from the sensor.

Give more details about your engine and vehicle. (4 or 6 cylinder)

Costee: Is it a 1994 model?

steveyen:

Thanks so much for your input.

It's a 6 cylinder 3.5L engine 2004 Maxima S.L (Dagrin)

GAZZUZZ:

When fixing your exhaust pipe make sure tell the person fixing it not to remove your catalyst. Very important.

steveyen:

Will make sure I do that. Thanks.

Could there be other symptoms to check out on the car or just the leaking exhaust? Cause people are telling me the following ;
-Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
-Three way catalyst converter Bank 1

GAZZUZZ:

U said you had a service engine soon light, not a check light, for all I know they may be stored codes from when your car was last worked on. But because you said "a deeper louder sound" and you went over "terrible roads" and your scan results include lower "catalyst efficiency" 1st thing to do is check for the obvious.

Do that rest car drive around for a day and rescan.

Costee:
Makes sense. Bank 1 is the one close to the firewall and nearer to the ground. The impact of the very rough roads may have unsettled things down below. But then lets hope that the catalyst converter itself was not already going bad and that the recent experience became a coup de grace. The knock sensor probably got triggered off in the process, not necessarily gone bad. I think OP should erase codes and scan again should SES light return to confirm.
Btw Gazzuzz, Service Engine Soon is used by Nissan for MIL, which is the Check Engine for some other makes. Or what do you mean by "check light"?

steveyen: I took my Maxima on a out-of-the-state journey and through some very rough Lagos roads ( Ajao estate bad roads, Barracks estate, ogudu terrible roads). After a couple of days I suddenly noticed ' Service engine soon' showing on the dashboard.

I did a scan on the car and got the following error codes:
p0420 - Catalyst System Efficiency Below Threshold (Bank 1)

p0328 - Knock Sensor Circuit High Input

Please what could these do to the engine? What is the implication of driving the car with these codes still on? How can these be fixed?

I also noticed the car makes a louder/deeper sound than before when revved. This happens after the codes now when I accelerates i do hear a more deep/loud sound.

Kindly help your inputs will be appreciated.