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Weird CEL issue....

doonze

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So my CEL started acting up again this weekend, it had been nice and dark for almost a month now!!

Pretty much, the past history is I've had CEL's in the past for both a bad MAF, and also a 176 code for a O2 running too lean. Replaceing the MAF and messing around with the O2 fixed both issues.

So Friday I'm heading up to pick up my son (a 120 mile round trip) and at about 80 miles my CEL lights up, no change in how it drives at all. I pull over after a bit and pull the codes just so I could see what was going on. I got 157, 172, and 176. I clear the codes and head on home. After about 3 miles the CEL comes back on and stays steady until I get home. (157 MAF low, 172,176 says both O2's lean)

Pull the codes again once home, same codes, all 3 of them. Clear them again.

Head back Sunday to take him back home, at about the 45 mile mark, CEL comes back on. Once again no problems with running, just the light. I stop several times for stuff and each time the light comes back by about the 5 mile mark and once it's on it stays on until I turn the truck off again.

So the weird thing is.... it takes about 50 or more miles until it comes on, once it does it will keep coming on. But if I let the truck rest, it won't come on again for about 50 miles. My 15 mile trips back and forth to work don't set it off, and the 10 mile trip to lunch today didn't set it off. Just LONG drives seem to do it.... and once it trips, it keeps coming back until it rest.

What could change after 50 miles that didn't change before that?

EDIT:
And for MrShorty... 111 KOEO, these are all CM codes. No other KOER codes either, just CM.
 
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Tbars4

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...This is normal operating procedure for your computer to run thru it's checklist...It takes about 50 miles for it to kick out the codes, after the codes have been cleared...;)
 
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Tbars4

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...It is possible that you did not have the battery disconnected long enough...I know I have done the same thing...

...Even though you do not have a light on till after 50 miles, you can still get info from the CM codes before the light comes on...
 
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doonze

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IC, I don't clear the codes by leaving the battery off, I clear by pulling the jumper during the test, then I rehook and check that they are clear (111 KOEO and 111 CM). But I didn't do that after my first test. (double check).

But I did double check yesterday, and got 111 on both, and I haven't had a CEL yet, so here in about 5 mins I'll run out on break and check the codes again and see if there are any stored.
 
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doonze

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Well, went out and tested, 111 and 111 on KOEO and CM. So no codes thrown. So this is what SEEMS is happening. If I go more then say 45-80 miles, I throw a CEL that won't go away until the truck sits. I cleared the codes Monday and verified they were clear, and today, Tuesday I check the codes again and get 111 passes.

In the last two days I made a 20 mile trip into town to go to Wal-mart and PetSmart, sat there for about 15 mins and drove home (another 20 miles),no lights no codes. Drove the 15 mile trip to work today, and drove about 15 miles on lunch, still no light and no code. I guess I'll have to wait until the weekend after next and see if my long trip throws the codes again.

This is just plain weird. Unless it IS tripping something, but the codes are not showing for 45 mins or so. In other words not getting stored until the light comes on, but are being tripped the whole time. Like the PCM is waiting to throw the codes. But I've had all the codes but the 172 before, and they would come on in minutes after the truck was started..... :dunno:
 
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Tbars4

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...The stored codes are faults that are present but have not failed...The CEL is a failure to achieve the proper feed back from a sensor...


...Your codes 157, 172,176 lead me back to your MAF..I would inspect the connections both mechanical and electrical as it may be heat related due to the time frame you mention...

......This might help for other places to start looking...

...Reasons for a p017X codes

A) Not the o2 sensors

1) Probably Vacuum leak
2) Clean the MAF
3) EGR tube leak
4) Plugs and wires

OR 5) Intake manifold gaskets..
 
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doonze

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Could it be possiable it's the cold air?? I mean could it be that my MAF is having trouble getting hot enough on the heater element and the cold air is making the problem worse. Cold would = LOW I think, but I would think the colder air would cause it to seem like MORE air was flowing, therefor it would inject more gas, and it would read rich, not lean...hmmm...


I did remove the MAF and cleaned it again.... so I guess we'll see..... Since it takes 50+ mile trips to set if off I'm not going to know for a bit....
 
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Tbars4

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...Your OP says you had replaced the MAF...This is a common fix for the code 157 and should have removed your 172, 176 codes...Did you also replace the MAS at that time..

..Are you saying you have an aftermarket CAI???...If so,that's an easy check...Just install your stock set up but I'm not so sure that's what you have so I don't know if that could the problem...

...Just me thinking out loud but if you only have the stock box on, a new MAF with sensor, I would thoroughly check the wiring to the MAF as I think it has a nick or burnt spot on it...Just my thought if all above is true...:dunno:
 
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doonze

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Ted,
Your confusing me, when I say MAF I mean the sensor (the black box with the two little thingies) and that I did replace about 2-3 months ago. I was getting 157 and 158 at that time, and it was cutting out. Replaced the MAF solved all problems except my 176. Removed the O2 and putting it back in (was going to swap them on MrShorty's advice but couldn't get the "good" one out) solved the 176 issue as well.

I didn't think we has a MAS... I was thinking a MAF (Mass Air Flow sensor) and a MAS (Mass Air Sensor) were different things hince why I'm confused. And we use the MAF...or maybe it's a MAP I'm thinking of?? Do we have both a MAF and a MAS?

Anyway....

No aftermarket anything, all stock. So if this keeps up I'm going to try and test all the wiring, maybe while it's throwing the light to see what's up? Thanks for the ideas!!!!!!!
 
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Tbars4

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...From the first post...
So Friday I'm heading up to pick up my son (a 120 mile round trip) and at about 80 miles my CEL lights up, no change in how it drives at all. I pull over after a bit and pull the codes just so I could see what was going on. I got 157, 172, and 176. I clear the codes and head on home. After about 3 miles the CEL comes back on and stays steady until I get home. (157 MAF low, 172,176 says both O2's lean)

...Ok, my bad on the MAS as you had already gotten me confused and that's easy...:D

:scratch:..Ok, you are not getting three codes, 157,172.176, as you originally posted..???

For the difference in MAS and MAF...;)
http://www.explorerforum.com/forums/showpost.php?p=1020989&postcount=5
 
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doonze

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...From the first post...


...Ok, my bad on the MAS as you had already gotten me confused and that's easy...:D

:scratch:..Ok, you are not getting three codes, 157,172.176, as you originally posted..???

Ok, now we're just confusing each other.

In the past I had gotten 157, 158, and 176 all at once. Replaceing the MAF fixed the 157 and 158. Removing and rescrewing SOMEHOW fixed my O2 176 issue that was left.

Since then no CEL codes...

Then the other night, got a CEL, pulled the codes and got 157, 172, 179. Cleared the codes, 5 mins later the CEL came back. 30 mins later pulled the codes again. Got the same 3 codes 157, 172, 179.

Cleared those codes. Then drove 50+ miles again and got the CEL. Pulled/cleared codes 1 more time (same codes).

Now driven for 2 day, never over 20 miles at once, and no codes or lights.
 
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Tbars4

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...Just for clarity, you just added code 179...

...I still stick with my answers in post #7 and post #9 to help you out with these codes...

...I am sure Mr. Shorty will have some better insight and I hope he will join in here...
 
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MrShorty

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CM172 is for the rear O2 sensor indicating lean. CM 179 is for the rear O2 sensor indicating rich. An interesting contradiction.

Have you tried putting a voltmeter on the MAF signal to see if the MAF is outputting anything reasonable (I forget numbers, but I thought Chiltons had some reasonable values in their "test MAF" section).

I've seen O2 sensors only fail "hot" -- meaning you'd have to drive a while (maybe even under harder than normal loads like towing) before they would do anything to trigger the code. Where you describe it taking a while after it's cooled down to come back on could be partially consistent with this sort of scenario.

Fuel delivery (pressure) reasonable? I would expect so, but it shouldn't take a whole lot of effort to verify.
 
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doonze

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Doh, see, that's why I shouldn't try and post at work (but i always do anyway)

176.... the code is 176, not 179.

So back to where I came from , codes are 157, 172, 176.

Thanks MrShorty, I was wondering if O2's could fail only after extended periods of use, maybe having something to do with temp. That was on my mind.

But I'm also with Ted, what if the codes are from the MAF acting funny and throwing the O2's off. In the past I just got 176, but now BOTH sides are saying I'm running lean, I don't think they would BOTH fail, so maybe I am running lean. Now the question would be why?

It runs perfect, before and after the CEL trips. Starts fine, I have no reason to suspect fuel, but I'll test it next weekend just to be sure....

I've avoided the Chilton's manual because I want to hold out for a factory service manual, just haven't had the $$$ yet. But maybe I need to pick one up, anyone know if the Haynes or Chilton's manuals are better for our trucks?
 
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