2001 Maxima "Service Engine Soon" Obsession

Has anyone ever solved the mystery of the Maxima Service Engince Soon indicator? My 2001 Maxima was running very rough for about 1 minute at startup when the engine was cold. It got worse as the outside temperature started to drop. You literally could not accelerate until the car decided it was good and ready to wake up. I have been seen idling all around Dallas! The diagnostics from AutoZone revealed a lean air:fuel ratio which could be caused by about 100 different expensive reasons. I replaced the Mass Airflow Sensor this week. It seems to have corrected the rough starts at cold engine temp but the darn light is still on. I disconnected the battery for 3 hours to reset the system computer, but that did no good. The light came on immediately after reconnecting the battery and starting the car. I am about to take the plunge on oxygen sensors, but was wondering if anyone has encountered this issue and found the correct repair. Any help would be appreciated.

“The diagnostics from AutoZone revealed a lean air:fuel ratio which could be caused by about 100 different expensive reasons”

I would suggest that you have the OBD II system scanned again, in order to make sure that the engine is not still running on too lean a fuel/air mixture. If it is, the cost of replacing burned valves will make you wish that you had pursued some of those “100 different very expensive reasons”.

You can pay me now, or you can pay me later. Later is almost always more expensive.

Thanks for the reply. Yes, the mixture is still lean. I had the codes read again last night. Unfortuantely, I do not remember the codes. They were the same as before I replaced the MAF (and like a dummy I threw those code printouts away). I totally agree on the preventive steps. I would prefer to pay the preventative price up front rather than after a major breakdown. But I’m not sure that the o2 sensors are the right next step. I don’t think it can be ignition coils (another possible cause according to the codes) since I have already replaced 3 of them and know how the engine behaves with a bad coil.

Using a shotgun to repair a car can get pretty expensive. You’re getting the codes pulled, don’t remember any of them, and are replacing parts that may or may not be needed. Now you’re wading head first into a questionable O2 sensor replacement.

Get the codes. Post them here as given. Do not assume that a particular code automatically means a part is bad.

This entire problem could be related to a dislodged vauum line or air leak.

Also get the fuel pump pressure checked.

The PCM codes are P0135 (bank 1 O2 sensor), P0171 (fuel in bank 1 is too lean) and PO174 (fuel system in bank 2 is too lean).

CONCLUSION: Thanks to the folks that provided insight. AutoZone reran the diagnostics and found P0135 and P450 (I think - indicated a possible bad catalytic converter). In addition to replacing the Mass Airflow Sensor, which corrected the rough idling during cold engine starts, I replaced the oxygen sensor (H02S1-B1 - bank 1, coming out of the exhaust manifold on the firewall side) and that cured the SES light.

I believe I have the same exact issue in my 2001 Maxima. The mechanic I took it too doesn’t know what’s wrong but I think I know after reading your post. I could bear to drive it and I don’t want to spend a fortune so…how much was the repair cost?

It sounds like you are doing your own parts replacement. Which is good. But if you are going to work on modern engines, you probably need your own code reader. Something like an Actron CP9125 will cost you maybe $80 and will work on any car built for sale in the US since 1996. I use a computer based scanner myself, but if I didn’t have an OBDII to serial converter and a drawer full of old laptop computers, I’d certainly spring for an inexpensive OBDII code reader. You want one that can at least read and clear normal DTC codes. More expensive versions have a lot of bells and whistles, and they make sense for a professional mechanic. But I think that I’d hold off on buying one of those until I encountered a problem that needed one – which probably will never happen to the average car owner.

Are you all sure it is the MAF? A posting on YouTube claimed that a new IACV and an O2 sensor did the trick for the same problem. I’m not sure which beast to tackle.