2005 Nissan Altima 3.5 Fuel too rich

P0172 - Fuel injectors have been replaced twice in the past 6 months due to it saying gas too rich
P0335 - (crankshaft sensor A was recently replaced)

I was driving along the highway and everything was going perfectly okay and all of a sudden it hesitated. I’m not even sure it could be called a hesitation. It quite quickly dropped to really low RPM’s all the way up to about 4 RPM’s and back to normal. the acceleration was really slow after that. I pulled into the nearest station to put on my live data ELM327 to read it while I finished my drive home. At that point, the car simply wouldn’t start. I let it sit for about half an hour and it eventually started with some prodding from my gas pedal and was able to pull those codes with my OBD II diagnostic reader after making it home. Any ideas on where to start?

Being that the fuel injectors have been replaced twice I’m having a hard time believing that it is once again the fuel injectors. I was looking at videos on how to test them with a screwdriver but seems like it would be rather difficult to do with the Bank 1 injectors being under the intake manifold.

I’ve also cleaned and tested the MAF sensor. The fuel pump is brand new as well.

Only time I’ve had that was with a maf sensor. First with stumbling like gas starvation, then rich fuel with a brand new maf. The long term fuel trim indicated a rich mixture.

Well since obviously the fuel injectors weren’t the problem, it’s time to consider the other things that could cause a rich mixture. Go get a real diagnosis or continue on this expensive route of just blindly replacing parts. Look at the data from the O2 sensors, MAP sensor. Starting with replacing was probably the most expensive of the guesses, doubly so since you did it twice, any may well have introduced more variables into the mix.


Did you happen to look at fuel trim data?

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I’m going the the P0406 as the problem

  • Possible surging while driving
  • Possible intermittent stall

Read more at: P0406 Exhaust Gas Recirculation Sensor A Circuit High


The first thing you do is inspect the air cleaner housing

If it’s full of acorns, that’ll cause a rich mixture


You haven’t tried replacing the oxygen sensors?

I think when one starts to go bad you get a check engine light for a failed oxygen sensor. When it goes all the way bad it seems like the computer isn’t able to determine that it is bad. It tests the sensor by varying the mixture and seeing how long it takes the sensor to respond.

Usually a bad O2 sensor reports that the engine is too lean, which makes the engine run too rich after it is corrected. I don’t know how this works. If bank 2 is bad causing a too rich mixture, could bank 1 be still working properly and detecting the problem? I assume it doesn’t have separate fuel trims for each bank. But I only know about single bank vehicles mostly.

Why would anyone replace O2 sensors when there isn’t a code indicating a problem with one?


Good point. Anytime the engine acts like it just doesn’t want to produce much power at all, or stalls, won’t start, one suspect which has to be considered is the EGR valve. It re-routes a little exhaust gas back into the intake in order reduce Nitrogen compound air pollution, and to prevent the engine’s innards from overheating. During idling, slow speed low power driving it remains closed, then opens on higher speeds and situations that call for more power, accelerations, going uphill etc. How it works on my Corolla, the computer knows when the EGR should open, and measures the temperature of a thermal sensor in the EGR pathway. If it increases in temperature the computer knows the EGR has opened.

the code says the sensor is indicating the EGR valve is opening and/or closing when it shouldn’t. I’m not sure whether this code means the EGR is open when it should be closed, or closed when it should be open. The first would cause poor engine performance and stalling, the second could cause engine overheating, misfiring, etc.

As far as my own experience, I’ve had similar symptoms on my older VW Rabbit, caused by a problem in the MAF function. I always test the EGR on my cars as part of a tune-up. I put a vacuum on it and make sure it stalls the engine. Usually when that test fails, it doesn’t stall the engine, meaning the EGR valve is stuck closed.


That has actually been part of the problem. I’ve had it in the shop twice now. Originally was put in the shop for a P0175 code. Once they said the issue was fixed. The second time they said the transmission was going out but didn’t offer an explanation as to how the two were related. (Side note: My transmission appears to be perfectly fine) Living in a small town in a fairly remote area my options of autoshops are pretty limited.

Thankfully the second time I replaced the injectors they were still under warranty so was just a matter of taking them back out and exchanging them. I’m hoping to be able to get out tomorrow and run my Elm to see if it comes up with anything. Although being fairly new to the Torque app I’m not real sure how to all the readings on it. If it continues like it has the last few times the issue has come up it won’t appear till after it has been driven for a little while.

I didn’t. Unfortunately once the engine wouldn’t start I unplugged it so there wouldn’t be an extra juice running on the battery while I tried to get it to start.

You could be correct. I was thinking of getting some WD-40 and trying to clean it out tomorrow morning.

That could be correct. I was driving about 65-70 mph when it hesitated on me. Being that it’s giving a code for it, it is certainly worth the time to try cleaning it and see if that makes a difference.

My MAF sensor seems to be working correctly. Although I won’t say that the quick test I did was 100% correct. A friend of mine had told me that if I unplug the MAF sensor while it’s running the car will shut off. That would mean the MAF sensor is working properly.

Not familiar w/your particular engine, but many modern engines use an electrical activated solenoid to control the EGR function. So you might try unplugging that connector as a test, for example when it won’t start, then it starts ok with the EGR electrical connector unplugged, that’s a pretty useful clue. I can’t imagine that WD 40 would have much cleaning effect on an EGR valve. Usually when they get gunked up, it is a very hard carbon deposit, nearly impossible to clean. If they can be cleaned, often have to use some sort of sand-blasting technique. Also if the EGR valve is gunked up, the intake manifold inner passageways are plugged up too.

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I wouldn’t take anymore advise from that friend.



@Tester , do you know if that code means the EGR is open when it should be shut, or the other way around? Or isn’t that possible to know just by the code?

Well I had a bad o2 also that was commanding a rich mixture. You can look at the changes in the signals to determine if it is lazy or not. But really, fuel injectors, transmission? You just really need a good diagnostician. I’ve never had a bad injector in a million plus miles, and certainly not all of them twice.

When I was at the dealer, the mechanic pointed to a vette in one of the stalls and said the owner was going to be pretty unhappy when he found out three of them were bad. I’m not a mechanic though, just drove a lot.

I thought that there could be a situation where the computer doesn’t determine that the oxygen sensors are bad. It’s better than replacing fuel injectors twice. It looks like George_San_Jose1 had a better idea. Unplugging the oxygen sensors can be a quick way to test things.

WD-40 is not a cleaner. It is designed to keep water from a component. Get the right cleaner for the EGR valve.


Just going from what Scotty Kilmer uses. A combination of carburetor cleaner and WD-40.