honda civic trouble codes...

[Elliot87]

hi my friend has a 99 honda civic and her check engine light is on....so i scanned her car with a code reader and heres what it said

system too rich (bank 1)
fuel trim malfunction (bank 1)

and i think the codes were like p0170 and p0172 or something like that. what could it be?

[XtremeModifier]

Well, I'd say o2 sensor or maf at the moment, although it could also be the tps (throttle positioning sensor). I'd doubt fuel pump problems, since that'd more likely cause a lean condition than rich, although under some conditions it might cause that.

It could be anything from a simple bad ground or shorted/burned wire to a fried ecu (I've had that happen several times now to my truck). I don't have the diagnostic diagram for that infront of me, so not much I could tell you.

[SjCiViCHB]

well you're running rich. Check you fuel pressure, for any leaky fuel injectors, vaccum leaks, faulty/dirty maf sensor, maybe even an O2 sensor...

[Elliot87]

see it cant be a trial and error repair. she doesnt have the money to be replacing all kinds of parts.....so i guess ill start by cleaning the MAF.....if that doesnt work i guess ill have her get a new o2 sensor.....and idk where to go from there. i guess ill take it 1 step at a time. i didnt know hondas had MAF sensors cuz my 91 integra didnt but i guess thats because it was obd1. anyways after i clean the maf and change the o2 sensor if theres still a problem ill check the wiring. where can i find wiring diagrams?

by the way idk if it helps at all but her car is shaking really bad when it idles in drive and its making a weird smell (probably unburned fuel) i dont know if it would be a fuel leak because its not burning gas that bad. its eating gas more than it should be but its not like going from full to empty in a couple of days. i'll keep you guys posted on my findings if im unable to solve the problem myself

[Elliot87]

well you're running rich. Check you fuel pressure, for any leaky fuel injectors, vaccum leaks, faulty/dirty maf sensor, maybe even an O2 sensor...


why would the fuel pressure be high?

[XtremeModifier]

Honestly, I'd take it in. If the cat goes, you'll be out quite a bit of money, and running rich does that to a cat after a while.

[Elliot87]

Honestly, I'd take it in. If the cat goes, you'll be out quite a bit of money, and running rich does that to a cat after a while.

well the problem hasnt gotten serious yet. the check engine light even turned off again. she said it goes on and off

anyways i had her start it up today....and i didnt hear any vacuum leaks...and i pulled the MAFS and it looked pretty clean to me. idk how it works though....its just a piece of plastic haha but it looked pretty clean. the wiring didnt seem loose or anything like that.

i told her go ahead and get a new o2 sensor and we'll start from there...

[XtremeModifier]

Well, the maf can be effected by even the tiniest amount of anything (oil, gunk, etc.) Doesn't even have to look clean - some clear-ish oil (like that used by K&N intakes) can get on it and damage it.

Glen, Rob, PNG, Ike/Ham and Eggs, etc. correct me if I'm wrong about that.

[Elliot87]

Well, the maf can be effected by even the tiniest amount of anything (oil, gunk, etc.) Doesn't even have to look clean - some clear-ish oil (like that used by K&N intakes) can get on it and damage it.

Glen, Rob, PNG, Ike/Ham and Eggs, etc. correct me if I'm wrong about that.


so should i try cleaning it anyways?


can anyone list off the most possible causes for fuel trim malfunction (in order of how common they are i guess)

cuz i need to know what to try first.

[XtremeModifier]

Well, the thing is, the stuff to clean a MAF is much cheaper than a replacement ANYTHING today. Thus the reason I suggested it - it did fix my mx6 with a similar set of trouble codes.

[Elliot87]

ok then i'll do that first.

its just one of those harder things to diagnose huh? cuz for the most part MAF/o2 sensors usually dont go out.....

[The Rob]

Correct me if I'm wrong here folks, but Honda hasn't been too big on using Mass Air Flow sensors. I really doubt there's anything to clean in this case.

I'd be looking for fuel pressure, TPS, and MAP readings at idle. If those are good, then you could have a plug that just isn't firing clean at idle. Worn plug/ closed gap, worn distributor contacts (if it has one) or a faulty wire. There's lots of basics to check. And of course it could also be a bad O2 sensor. If you don't know how to check all these things or have the tools to do so, take it to someone who does. For me there's nothing worse than diagnosing a car that some amatuer has tried to half ass fix already.

[Elliot87]

Correct me if I'm wrong here folks, but Honda hasn't been too big on using Mass Air Flow sensors. I really doubt there's anything to clean in this case.

I'd be looking for fuel pressure, TPS, and MAP readings at idle. If those are good, then you could have a plug that just isn't firing clean at idle. Worn plug/ closed gap, worn distributor contacts (if it has one) or a faulty wire. There's lots of basics to check. And of course it could also be a bad O2 sensor. If you don't know how to check all these things or have the tools to do so, take it to someone who does. For me there's nothing worse than diagnosing a car that some amatuer has tried to half ass fix already.

well i dont have the equipment to read the tps or map readings at idle....i do have a fuel pressure test kit....and yes i know honda isnt big on using MAFS's but hers civic actually does have one. and again i dont understand how a faulty plug or distributor would cause it to run rich....i always figured problems like that would lead to the car running lean as opposed to rich.

[XtremeModifier]

Correct me if I'm wrong here folks, but Honda hasn't been too big on using Mass Air Flow sensors. I really doubt there's anything to clean in this case.

I'd be looking for fuel pressure, TPS, and MAP readings at idle. If those are good, then you could have a plug that just isn't firing clean at idle. Worn plug/ closed gap, worn distributor contacts (if it has one) or a faulty wire. There's lots of basics to check. And of course it could also be a bad O2 sensor. If you don't know how to check all these things or have the tools to do so, take it to someone who does. For me there's nothing worse than diagnosing a car that some amatuer has tried to half ass fix already.

Yep, on the last part, that's one reason I recommended a professional. With a pro (i.e. you, glen, etc.) they'll go straight to the heart of the problem and fix it. With mechanical problems, someone like myself with a little knowledge here and there can get it figured out and patch it up. But electronics are not my thing... at least not yet (working on that), and in particular, I suck with signals (good with dc constant voltage, constant resistance). And it's that experience and lack of "throw something at it and see if it sticks" that you pay for - something which pays for itself in a lack of guessing games and saved time.

Sorry about the MAF thing - Mazda was huge on MAF's so I assumed that Honda was similar (they're both japanese) and iirc Chevy also used maf's.

Elliot - listen to Rob on this one. While I'm just a mere shade-3 mechanic, rob's ASE-cert'd (last I heard anyways).

[Elliot87]

Yep, on the last part, that's one reason I recommended a professional. With a pro (i.e. you, glen, etc.) they'll go straight to the heart of the problem and fix it. With mechanical problems, someone like myself with a little knowledge here and there can get it figured out and patch it up. But electronics are not my thing... at least not yet (working on that), and in particular, I suck with signals (good with dc constant voltage, constant resistance). And it's that experience and lack of "throw something at it and see if it sticks" that you pay for - something which pays for itself in a lack of guessing games and saved time.

Sorry about the MAF thing - Mazda was huge on MAF's so I assumed that Honda was similar (they're both japanese) and iirc Chevy also used maf's.

Elliot - listen to Rob on this one. While I'm just a mere shade-3 mechanic, rob's ASE-cert'd (last I heard anyways).

okay then....and also what does the whole shadetree mechanic thing mean? i hear alot of people use that term

[XtremeModifier]

A shade-3 mechanic is kinda like a do-it-yourself'er. Most automakers (i.e. the new bmw's) are making it increasingly difficult for regular people to do their own auto repair. This is a decent definition I found on Urban Dictionary:


A person willing to learn and perform scheduled maintenance or simple repairs on their own vehicle rather than being completely reliant on technicians who may be dishonest, careless, or ignorant.


It goes beyond simple repairs sometimes - some shade tree mechanics will build their own engines. But, for more complex jobs like that, it's usually a good idea to leave it to the "experts". Although, doing your own work can be fun, especially combined with beer, pizza, and a bunch of friends.

[The Rob]

Elliot - listen to Rob on this one. While I'm just a mere shade-3 mechanic, rob's ASE-cert'd (last I heard anyways).

ASE master + advanced engine perf. certified. Acura (which pretty much means Honda too) certified master. Former Acura dealer shop foreman. SPent more than half my career working on Honda/Acura...yeah you could say I'd be one to listen to on a Honda drivability problem.

[Elliot87]

ASE master + advanced engine perf. certified. Acura (which pretty much means Honda too) certified master. Former Acura dealer shop foreman. SPent more than half my career working on Honda/Acura...yeah you could say I'd be one to listen to on a Honda drivability problem.

damn and you dont live in socal huh? haha

[XtremeModifier]

ASE master + advanced engine perf. certified. Acura (which pretty much means Honda too) certified master. Former Acura dealer shop foreman. SPent more than half my career working on Honda/Acura...yeah you could say I'd be one to listen to on a Honda drivability problem.

I'm more of a diesel-guy anyways, lol.

[The Rob]

Black hands for life.

[RAWbin]

holy fuckass its the rob. hey rob do you think ill kill myself for sure if i get a c5 z06?

[The Rob]

C5s are plenty safe. Just never turn off traction/stabililty control if you doubt yourself. If you drive like a tool, then you won't need a Corvette to do the job. You can kill yourself in a VW Eurovan or some other similarly slow as fuck vehicle.

[XtremeModifier]

So, Elliot, how's the work coming along? Any updates?

[RAWbin]

C5s are plenty safe. Just never turn off traction/stabililty control if you doubt yourself. If you drive like a tool, then you won't need a Corvette to do the job. You can kill yourself in a VW Eurovan or some other similarly slow as fuck vehicle.

Yeah I was just wondering because I've had an Integra then a CRX. Now I feel like its time to step up. I was thinking either an '05 GTO or a c5 z06. I drive fine but all that power at my feet could mean trouble lol.

[The Rob]

'05 GTO has the 6.0L right? That would be a sweet car to have for a daily driver. More practical, rides better, and not nearly as attention getting as a Z06.

[RAWbin]

yes sir the 05's are 6.0 and I really love the way they look.

[Elliot87]

So, Elliot, how's the work coming along? Any updates?


Actually been kinda busy lately. i told her though that its gonna be hit or miss....and if she has the money she should probably take it in, but i told her what the possibilities could be and that we could try that before she takes it in. i've just been so exhausted from work i havent done much lately haha

[GlenB]

Lean and rich fault codes have the longest list of possible faults out of any fault code.

Do you have a scan tool that can read not only codes, but data stream? Even if it is just generic data, it will be helpful.

If you can see data streams, look at the Short term fuel trim and long term fuel trims. Post up the trim values at idle when hot, and at 2000 rpms free-rev when hot.

When you first start with a cold engine, after sitting over night. Compare the coolant temp sensor to the air temp (you'll probably have to use a reg. thermometer for air temp if all you have is generic data). Do they match? What is the coolant temp sensor reading at the moment the thermostat opens for the very first time at warm up? (when the rad suddenly gets hot).

Pinch the EVAP purge hose with pliers while watching the fuel trims at idle. What do they do?

After idling for a period of time at first start up... no reving... is the EGR valve hot?

[GlenB]

why would the fuel pressure be high?

Stuck pressure regulator or otherwise restricted fuel return line (like pinched closed)

[GlenB]

i know honda isnt big on using MAFS's but hers civic actually does have one

I just looked at a 99 Civic last night (a used car purchase for someone). It had no MAF sensor. Are you sure that wasn't an air temperature sensor you saw? It did have an air temp sensor stuck in the intake snorkel. The only other thing on the snorkel was an intake resonator.

The 99 Civic I saw uses Speed/Density. Meaning, it doesn't measure air flow. Instead, it infers air flow from TPS, RPMs, Air temp, MAP/BARO, and the fact that the PCM "knows" the displacement. It knows that an engine of "x" displacement, with a throttle angle of "XX", running "XXXX" rpms, that has "X" amount of absolute pressure in the intake, with an air temp of "XX" a barometric pressure of "X" (infers altitude) should have approximately "XX" grams per second of air flowing into the cylinders. It then uses the O2 to fine tune it.