Honda_Enjineer

Hi,

My 4wd Pilot EX has now 73K miles and it has started throwing MIL = P0175.

This is the 2nd time - last time I replaced the EGR valve and it seemed to resolve the problem for a few months.

Car is VERY well maintained and I just changed the plugs the this morning but to no avail. I mainly do high speed freeway driving.

I'm seeing ST and LT fuel trim values in excess of -10% on Bank 2 and these values are clearly too high.

By the way, P0175 is System Too Rich (Bank 2) - which I already know.

I'm hoping that someone else here had this issue and has resolved it already to save me time diagnosing the problem.

Please don't just post what the Honda manual says as I already looked there too (fuel pressure, valve clearances etc, etc...) - yes I know that, but I'm guessing that 99% of the time this code is caused by problem X (whatever X is).

Anyway, I'm hoping some Honda expert here knows what X is most likely to be

Thank you for any good hints!

Bob

Honda_Enjineer

I'm posting this to help out other Pilot owners with P0175 (or P0172?)... (basically answering my own question above again but this is the info I was looking for myself with my first post - so here goes).

I looked at the options for addressing P0175 in the manual and I decided that checking the valve gaps was something that wouldn't cost me anything except my own time and it was probably worth doing it anyway even if they turned out to be fine at ~73K miles.

Today I spent 3 or 4 hours doing just that and I was surprised at what I found.

My interesting discovery was this -> NONE of the inlet valves needed adjusting. Every one of my exhaust valves had practically NO gap left (this was with a cold engine too) !! Was shocked by this

I adjusted and re-gap'ed all of the exhaust valves and reassembled everything. Did the "idle learn" procedure as outlined in the Honda manual.

All of my fuel trim values are now positive values instead of negative. Bank 1 and bank 2 are now showing similar values for both ST and LT and all are within specs.

Interesting too - throttle position is now lower by a few percents and the vacuum MAP in.Hg value has also decreased to around 8 or 9 on idle. The engine now seems to idle a little smoother to boot.

I was shocked that the valves had absolutely NO gap left! I've done mostly freeway driving - so not sure if that was a factor but I reckon that I caught this issue just before I ended up with a burned exhaust valve or seat.

Anyway, I'm pronouncing the issue now cured and I'll add another entry later to this same thread if the code ever returns.

Otherwise I hope that this info helps out someone else. The task took me a while to do so I'm not sure what a 'stealer' would charge for it but I'm guessing not cheap.

Bob

HondaDIY

Greetings Bob,

Interesting... can you tell me if you had any audible clues in the miles prior to throwing the code, or change in mpg?

We have a 2006 Pilot 2WD - the one with the three cylinder "eco" mode - with 64k+ overwhelmingly highway miles; stumbled across this thread searching the web for some clues as to what I've started experiencing over the last 1500 miles or so.

A little obsessive - I think I've tracked every gas tank's mpg since new - the Pilot settled in to a solid 23-24.5 mpg for tens of thousands of hi-speed highway miles, consistent regardless of temperature/time of year. About 5 weeks ago I noticed the mileage beginning to slowly drop, with my last trip this past weekend being slightly more than 21 mpg.

Looking back, I noticed that sometime during these past weeks I became aware of a very soft, subtle yet audible sound that I can best describe as the valves rattling or knocking - as if I had low octane gas in some older, pre-ECM vehicle - whenever eco-mode is engaged, i.e. 30 mph or more, and disappears if I bring in more gas to engage all 6 cylinders with a push on the pedal. I lose this sound as I approach external wind resistance noise around 60+ mph in eco-mode.

I know you don't have a three cylinder mode in your 4WD but, in looking back, any aural clues or a change in your mpg before the codes were thrown?

Thanks in advance,

Harry

Honda_Enjineer

Hi Harry,

I noticed no sound and I wouldn't expect to since all the exhaust valves were all too tight (a valve sound is typically heard when the valve gaps are too large - or, also on a cold engine which is the same thing really). If you are hearing an (irregular) valve sound on a hot engine then it might be a different issue entirely.

As you know my Pilot is the 4wd BTW so your mileage is always going to be a bit better than mine (I'm typically 20 mpg on long drives).

BTW, I added irregular because if I listen really critically to my Pilot at idle (especially with the hood open) I can always hear a little valve-train noise even with a hot engine and with all the gaps now correct. But I'm sure that this sound was there even when the car was new and you don't hear it under normal driving conditions because it is just a tick tick tick. So try to be sure that your noise is something new and really something wrong - otherwise it may be just a red herring.

For example you might have a sticking or burned valve.

BTW, you didn't mention any MIL code? Is your check engine light on?

With 64K miles and knowing what I know now about these engines I can almost guarantee that checking your valve gaps would be a good thing to do (as per my posts above).

The main symptom I noticed before getting P0175 was a very slightly irregular idle - like a very occasional miss in the beat. But now it idles how a Honda should and sounds very very regular just like a fast quartz watch, it never misses a single beat any more.

Bob

HondaDIY

Wow... thank you for the rapid reply, Bob.

No... no codes showing yet, which is why I was wondering if anything in an audible way predated the codes being thrown and your discovery of the problem and its solution.

For my own edification if you know, why is it that highway miles/low rpm usage - I figure that the VAST majority of our miles have been spent on the highway in the 2100-2300 rpm range - leads more quickly to exhaust valve clearance problems, or am I wrong on this point?

TIA!

Nick

Honda_Enjineer

Hi Nick - no noises except slightly irregular idle which you usually feel (more than hear) with your hands on the wheel as I said earlier.

I'm not sure that the type of driving makes much difference. I do mostly freeway and my wife does mostly town driving. Both our engines needed the valves adjusted and both are fairly close in mileage.

I'd venture to guess that it is more a factor of the engine design itself - red hot exhaust gases leaving via red hot exhaust valves which are constantly whacking on their aluminum valve seats. That just slowly wears away at those seats over time because the material itself (aluminum) is fairly soft especially when it gets very hot.

The most telling factor for me is that ALL of the inlet valves were fine in the two engines that I did. They of course are constantly being cooled by the air and fuel mixture coming into the engine. So those valves have an "extra" cooling system of their very own.

Self adjusting valves might be a design improvement but because of the VTEC head there isn't much space for them.

BTW, I've had other cars in the past that had burned exhaust valves - but I've never yet heard of a burned inlet valve

Bob

HondaDIY

Thanks again for the quick response, Bob... I think I'll try posting my car's problem/observations as a main thread and see if I get any responses: so far nothing over at Piloteers.org except for looking.

Honda_Enjineer

For the record this problem still appears to have been completely resolved by my valve adjustment job - it has now been about a month since I did the valve work.

The car is still running beautifully and idles VERY smoothly. No more MIL's since then.

Ross 2.0

What year pilot is this? Sounds like you might be a candidate for the software update too.

Ross 2.0

Check the fuel pressure.

Is the fuel pressure OK? YES - If you are troubleshooting DTC P0171 or P0174, go to step 2. If you are troubleshooting DTC P0172 or P0175, check the valve clearances, and adjust if necessary. If the valve clearances are OK, replace the injectors, then go to step 2.
NO - If the pressure is too high, replace the fuel pressure regulator, then go to step 2. If the pressure is too low, check the fuel pump, the fuel pressure regulator, the fuel filter, and the fuel feed pipe, then go to step 2.

bryse68

adjust valves and perform ecm/pcm software update....

Honda_Enjineer

Thanks guys but the valve job did the trick - no more problem or MIL. So not necessary to be messing with things that are working just fine like the software. If it works DON'T FIX IT as they say.

BUT... I strongly recommend anyone with a Honda VTEC engine to be thinking about checking their valve gaps around 50K+ miles instead of 100K+ miles and I started another thread to stress that point.

Bob

therichersons

I have an 04 Acura MDX which from what I understand is nearly the same or the same as the pilot 4x4. My vehicle has had the engine light coming on and off for about a year now but recently it has been staying on, sometimes the VTM-4 light comes on as well. The symptoms were an idle that consistently dipped so low that the car almost died, at stoplights, parked, etc. It always died on the first cold start of the day and we were getting poor gas mileage. The code that it was throwing was P0175, we read a lot of threads online, talked to a couple experts and from this decided perhaps we had a faulty EGR valve. We changed that out and the car appeared to be fixed. Our MPG's jumped from about 15.9-16.5 to about 19.5. The idle was smoother and it stopped dying on the cold start and the engine light was off. This lasted for about 5 days. Then one day the engine light came back on along with the VTM and the car seemed to be running worse than ever. Sure enough now the vehicle is pulling codes P0172 & P0175, my gas mileage is down to 15, it dies on the cold start and the idle is rough again. I have talked to a few ppl who have suggested the valve adjustment which is what helped Bob on here. That is our next step. My question is, does anyone know why my vehicle would be running better and seemingly fixed after the EGR replacement only to get worse after a few days?

Honda_Enjineer

You are going through exactly the same process that I went through. I believe that after I swapped my own EGR valve there was a few days where the computer "relearned" things before concluding that the problem really wasn't fixed. Yes, mine did EXACTLY the same thing.

You'll be very happy to know that adjusting the exhaust valves fixed ALL the problems and the engine again idled smoothly just like a Honda should. It also seemed to have more power.

My P0175 code has never returned and the car continues to be happy. I'll be doing the timing belt on it quite soon (80K miles) since I've learned not to trust Honda lifespan estimates.

Bob

BobSproket

In retrospect changing out the EGR valve was a red-herring in my case although it certainly didn't hurt anything (except my wallet).

Bob

Honda_Enjineer

For the record the V6 engine on an MDX is identical to a Pilot. It just says Acura on the top of it instead of Honda.

Over time the exhaust valves (which get very hot) recede slightly into the soft alloy head and the valve gaps disappear. This leads to rough idling and P0175 being thrown.

NZKIWIS

Had the valve adjustment done after getting codes P0172 and P0175 at a Honda dealership as I was driving out the gate the engine check light came back on after Honda told me the car was good to go. I have cleaned the MAF sensor and test drove the car .... 50 km later the check light came back on .I'm now looking towards the fuel injectors as being the cuase of the engine check light returning with the same 2 codes. It's a 2006 Jazz with the L51A engine has done 95,000 km I don't like the Honda dealership so I'll try to find a solution as I think the dealership likes the idea that you have to come back a couple of times and get you to off load more cash...they have the factory scanners etc to work out what the car is doing I did ask did they perform a trim after the valve adjustment ...the was no need too.