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Check Engine help: p0171 p0174

28K views 16 replies 5 participants last post by  Fredsvt 
#1 ·
Hey all,

I have a problem... My check light comes on and goes off once a day or once every other day... I was hoping to get through inspection during an 'off' period, but the light came on as I was waiting on line at DMV- just my luck. Any way, they said my light was on with codes p0171 and p0174. Also I remebered reading the codes back when this started because under hard accelerations (>5500rpm) I will also get a misfire blinking check light, but as soon as I let off the gas and roll the light will stop blinking, and then by the next day will completely shut off.. I have made 0 attempts to diagnose this. I plan on buying a more comprehensive obd reader soon (pc based as opposed to pocket code reader)... Does anyone have an idea on what would cause this sporadic on and off event from my check light reading those codes? Or does anyone have any similar experiences?

Thanks in advance
 
#2 ·
Quick google.

Most likely the cause is a vacuum leak. A vacuum leak can be caused from a vacuum hose, intake gasket or maybe even a leak in the air intake hose from the MAF (Mass Air Flow Sensor). Listen for a hissing sound that may lead you to the source of the problem. Some technicians will use a propane bottle with a hose attachment to help pinpoint vacuum leaks. With today's computers it's not quite as easy to check for vacuum leaks this way because the ECU (Electronic Control Unit) will compensate quickly for the added fuel and a change in idle is harder to notice. Oxygen sensor readings can be monitored with a scan tool while checking for leaks with propane, by looking for increased readings when enriching the mixture. Another way technicians can check for vacuum leaks is with a smoke test. By introducing smoke into a vacuum hose on the engine, the leak will be revealed when the smoke escapes from the problem area.

Aftermarket air filters that use oil on the element can sometimes damage the MAF. Over oiling the air filter may allow some excess to get on the MAF sensor wire or element. This can alter the reading, fooling the ECU into seeing more or less air flow therefore changing the air/fuel mixture incorrectly. I once worked on a car that would not start that had a problem with a MAF. When looking at the wire in the MAF, there was a burned piece of trash that made it's way past the air filter. After cleaning the sensor the car ran perfectly. The ash that was on the MAF sensor wire was altering the reading by enriching the mixture so much that the car could not run. After talking with the customer, he said the air filter was just changed. This was obviously when some trash got into the air intake hose that settled on the hot wire of the MAF.

Fuel Pressure could also cause a lean condition. If the fuel filter is clogged or the fuel pump pressure is low, there could be higher level of oxygen in the exhaust also. Most of the time though, the ECU will compensate for the reduced fuel volume. So this is one of the least likely causes of a lean code.
From here.

More google.

* PCM software needs to be updated
* Vacuum Leaks (Intake Manifold Gaskets, vacuum hoses, PCV hoses etc.)
* Mass Airflow Sensor (MAF)
* Plugged Fuel Filter or weak Fuel Pump
* Plugged or dirty Fuel Injectors
From here.
 
#3 ·
Thanks for reply.. That's a good list of stuff there.. Being optomistic I would hope there's no pump related problem which seems to be the least likely in that article.. I'm also assuming I could rule out the mag sensor under the impression that my car doesn't have one I think ? 04 v6 6spd= someone correct me if I'm wrong.. Based on that article I would go with vacuum leak.. But I wonder why it would go on and off every few hours or so.. For example... I'm at work now (iPod touch on wifi) delivering pizza. When I woke up, check light was off... When I wrote this thread before it was on, and now shortly after it is back off. On days where I do a lot of hard accelerating I do notice a smell afterwards so I don't doubt that the light is lying.. Just can't explain it
 
#4 ·
I don't believe 03-05 have the MAF sensor so you can rule that one out. I'm going to go on a whim and say that it's probably a vacuum leak. I say get it checked out as as soon possible.
 
#5 ·
An idle indication of 2 banks of lean codes has to be only a couple of things, vacuum leak as mentioned, the leaks have to effect both banks, so it's a common leak, not specific to one bank or the other. Possible low fuel pressure, which also can cause it to lean out bad enough when revving to cause a misfire. (can also burn valves)

How many miles are on your car?

Also, a basic obd2 scanner won't be of any help with diagnosing fuel control issues when they get as bad as yours is at now.

Even with the light off, those codes were stored, and NJ inspection would have failed you anyway, even with the light off.
 
#6 ·
I have about 107000 miles on it. And yeah I more hoping that I would just pass hah... I plan on fixing it but I rather do that on my own time than have a 45 day limit imposed on my.. I don't have the money for whatever it is now so I was hoping to hear some encouraging words from someone with a similar problem..

That's not the only problem I have with the car right now it's just the only one I don't know where to start with right now... I have find a way to prioritize my little list and hopefully work in the rec'd timing belt servce
 
#7 ·
Ok, at 107k, the valve adjustment needs to be checked asap.

Sometimes lean codes and misfire issues are the first sign of tight exhaust valves on a J30, esp the A4, A5 variants.

I'd definitely get valve cover gaskets, and have the intake upper plate and upper manifold to runner gasket, and throttle body gasket on hand. I pull the throttle body to pull the intake, so as to not disturb the coolant lines to the throttle body.

How does it run when cold?
 
#8 ·
Runs fine cold.. Just within the past week with temperaures under 20 I been having trouble with my ps pump... But it's fine when it warms up.. That's not giving me any stress though because when I changed my tie rods a few weeks ago I noticed the seals leaking so I'm guessing water is getting absorbed somewhere.. The fluid almost looked frozen I was almost thinkn that not much else could go wrong hah but at least I know what's wrong with that...

Besides that, runs perfect when cold... I think maybe once this past year it felt like it was guna stall when starting but that was very out of the ordinary and I drive about 400 miles a week minimum and it hasn't done that again.
 
#9 ·
There is a bulletin or service news writeup on the tie rods, did you get Honda tie rods with the new boots? The old boots on some '04s can allow water in, which destroys the inner joints.

Did you see water in the boots or p/s fluid?

I'd still definitely check valve clearance, and while the intake is off, check for any place that could be a vacuum leak.

If you can get it, I'd need fuel trims both banks Short term and long term under these conditions:

Idle
unloaded 2500 rpm
cruising at about 2000 rpm in 5th gear should be good
at about 75% throttle, 2nd gear at around 5500 rpm, short term trim.

Also, I'd like to see a/f sensor voltage, both front sensors, during a wide open throttle run.

Does it seem to have the power it should when getting on it, or does it "lay down"/bog?
 
#10 ·
AGH! are you serious.. they looked at me like I was crazy when I told them this I had no idea there was a service bulletin.. i took pictures of the dis-assembly of my old inner and outer tie rods, and boot that looked disgusting on the inside definite water in the boot that was clearly loose without touching it, and of the leaking seals.. I bought new inner/outer tie rod, new boot, new clamp from them. I'm almost positive I had that tie rod replaced by them under warranty 8 months ago and it looked like they left the old boot on (using a zip tie to hold it in place which clearly didn't hold).. I have all of the old damaged parts riding in bags in my trunk that I meant to go and show them but I figured I didnt have time to argue recently.. here are pics.. I have been tight for money and otherwise would have never just slapped on new tie rods and a boot:







I bought the parts before I noticed any of this, so by the time I was done I figured my ride to the dealership could wait. I went by when I was passing and had a few mins and they seemed to have no idea what I was talking about and maybe it was put on wrong and when I mentioned they were the last ones to touch it that tune quickly changed.. I havent had a chance to go by yet.

Do you have any more info on this service bulletin? And would they be liable for the power steering problem considering they worked on my car within this past year and it wasnt even addressed?

Back on topic however... I could try to work on getting that together.. Atm I have no means of pulling that information (though hopefully soon I will).. It seems to have power just fine.. If I didnt get a blinking check light under a lot of throttle I would probably not notice a problem.. If its held around 5500 thats when it will pop the light.. For example, if i floored it through 1st/2nd/3rd, i wouldnt get a light unless I left it around a high rpm without shifting (modulating gas around wide turn at high rpm for example).. Recently I dont notice those problems because I've been very cautious with the car. Dont want to add any extra stress until i get everything sorted out.

Another thing about acceleration however is the clutch. After hard acceleration (say coming to a stop then taking off again) the clutch pedal will be extremely difficult to control.. Stiff and squishy.. but it wears off withing 15-30 seconds... Only hard accelerations.. Speed makes no difference (clutch will act fine gradually picking up to as much as 85 as i tested)

Feel like im beginning to pour my soul into this post hah so I will end here. Feels like everything is going wrong all at once
 
#12 ·
Thanks!.. I'm trying to be optimistic.
 
#13 ·
I've attached the tie rod bulletin.

The clutch issue is odd. It gets hard to push, but yet feels spongy? Does the take up point change when this happens? Any vibration or noise?

Did you complain of front end issues when the car was last worked on? If so, I think anyone could see the rust pouring out of the inside of that boot.

The check engine light flashing does sound like the problem the '05s had with incorrectly detected misfires. Have you had the battery disconnected lately, or did it go dead at all? If you clear the codes, drive it to make the light flash, does it store misfire codes? Is the lean code problem only showing at idle? Can you access freeze frame data?
 

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#14 ·
Thanks for the bulletin..

yes the clutch issue is odd.. it takes up about the same point (which is pretty high on my car for the past year)-- maybe higher if anything.. its stiffer to push until u pass that point, then it feels loose.. trying to take off in first is a real task.. the pedal is jumpy... when its pressed all the way down its extremely easy to push, but gets increasingly harder to maintain force as you let up... kind of like stretching a rubber band which will all of a sudden pop... after such acceleration, theres a lot of bucking taking off in first as i normally would (i would definitely stall if i wasnt paying attention).. but it only lasts for a few seconds.. if i pump the clutch it seems to work it out faster, but its so short of a period of time i could be imagining that effect. :dunno:

in general however my clutch doesnt engage until im almost fully off of the pedal. not good. :(.. actually im just realizing that on my way to dmv i did disconnect my battery to swap out the hid bulbs for stock... but regardless of that it was an issue before that... in january 09 i read my first misfire with 1 2 3 4 5 6 random.. then a week later i think it was 1 3 5 or just 3 5.. and then it never came back.. i was in florida at the time and a friend of mine happend to have a pocket reader on hand.. i drove all the way back to nj fine and never saw any codes again until recently with this on off on off on off business.. its completely unpredictable though, because they didnt come on at all yesterday or today. ill have to try to clear drive and check the codes.. hopefully it wont be too difficult to make them come back on with how unpredictable it is. the lean codes seem to have a mind of their own... and typically (now that i think about it) only come after driving around, shutting off for a bit, and coming back and starting and it will be there.. i dont think it has ever popped up as i was driving, if that makes a difference (though i dont want to say that it never has)
 
#15 ·
I don't like that clutch action. It sounds like you're getting close to clutch time.

i have a feeling the pressure plate is having a problem. Since you're nearing the disc's end of life, by the high take up point, the pp may be moving too far and that's what you feel. I'd live with it for now.

I can't see it being hydraulics as it should be very consistently soft or spongy.

It couldbe like some other cars I've seen, they only do this once... You push, the pedal is extremely hard, then you push, it "snaps" and falls to the floor. You pick up the pedal, and push, and the release bearing is pushed THROUGH the fingers on the pressure plate.. Once that happens BOOM, the entire clutch assembly usually explodes.

I'm hoping your car's PCM, at some point, hasn't lost it's low and high speed crankshaft profile "learn" values.

If, once you've checked the valve adjustment, and made sure there's no vacuum leaks, etc. You may need Honda to check or someone with a Honda HDS to make sure the high and low speed profiles are learned. If they aren't it'll need to be done.

Since you have normal power output, you can at least not suspect low fuel pressure, or exhaust restriction (cat plugging) issues. I'd expect if it had either to have low power or bogging issues.

When you notice the lean code MIL, after hot shut off, does the car seem to rev slower very briefly as you take off, or is it almost instant once the car is running? Any difficulty warm/hot starting?
 
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