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Discussion Starter · #1 ·
My truck has 265,000 miles on it and runs and drives great. Check engine light comes on, I record the codes, erase them and it takes about a month for them to reappear. Here's the list:
P0442, P0455, P0172, P0126, U1026, U1064,
I've replaced (in order) gas cap, Purge valve solenoid, and vapor canister vent solenoid. All A/C Delco parts. It runs and drives fine, but I've recently noticed a skip and hesitation for a few seconds when I first crank it up, but that went away a couple of days ago when I erased the codes. Any ideas guys? It's a rust-free truck, so I don't think there's a problem with gas tank rust around the fuel pump. This is a great truck, and I don't mind spending a little money on it to get things fixed if needed. I just replaced upper and lower ball joints. front hubs, inner and outer tie rod ends and sway bar struts were replaced about 6 months ago, so I like to keep up with all routine maintenance and do all the work myself. Just looking for any input from any of you that may have had these codes. Also, I replaced the exhaust manifold with a header about a year ago and did a cat delete on the main catalytic converter (not the pre-cat in the header), and used the spark plug anti-fouling adapters to "trick" the computer into thinking the cat was still there. There were no codes after that little trick. Hopefully ya'll know what I'm talking about there.
Thanks in advance for any input. I love my truck and want it to last forever!!
 

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P0442/P0455, EVAP leaks. You have replaced all of the nromally defective parts. Could be a crack in the canister. Could be a defective tank pressure sensor. Could be a deteriorated/cracked EVAP line or hose. You have an Extended Cab, so the tank pressure sensor can be accessed through the wheel well.

P0172 Rich condition. Can be caused by the MAF Sensor. Try cleaning/replacing it. MAF cleaner available at auto parts.

P0126? Can't find that code in any of the GM Colorado Service Manuals. Google says 'operating temp too low'. Is the engine temp gage in the normal midrange when warmed up? If not, could be thermostat stuck open. If your scan tool can read live data it should give you the operating temp in degrees.

U1026: Lost Comm with Serial Data Bus
U1064: Lost Comm with Serial Data Bus.
Are these reoccurring DTCs? Could be a power problem. Has the battery been disconnected with the key on? Maybe check battery condition.
 

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Discussion Starter · #3 ·
Great ideas Cart! P0126 was my error. Actually P1026 - which you addressed. I did have to replace my gas fill door a few months ago. That requires loosening the filler neck screws and wiggling it around a bit. I bet you're right and I cracked a brittle, almost 20 year old hose. Last time I got a too rich code, it was because the exhaust manifold was actually cracked and came out in 3 pieces when I replaced it! I know an bad exhaust leak pre-cat will throw that code. I'll clean the MAF, but also check my clamps where I replaced the main cat with a length of pipe.
Battery is great and I've not disconnected it for any reason. I read where the U1064 could be no communication with the DIC, and U1026 could be no communication with the transfer case. No problems that I'm aware of, and I put the truck in 4wheel low and 4wheel high and everything seems to be working fine.
Thanks again for the help. As the user name implies, I'm an old guy and forget a lot of details. You reminded me of the prior "too lean" code and the possible reason for the evaporator issues. As always, I appreciate you and all the help you provide here!
 

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Regarding the P0172 rich condition. Another quick check. Disconnect the vacuum hose that goes from the fuel pressure regulator to the front left side of the resonator. Any evidence of fuel there is an indication of a leaking regulator, which will put unmetered fuel into the intake.
 

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Discussion Starter · #5 ·
Haven't had much time to check things out, but the truck is idling terribly and shudders and has shut off a couple of times at traffic lights. I'm sure that's caused by the too rich code and the computer is cutting "trimming" fuel supply to compensate for that. I disconnected the hose from the resonator and didn't smell fuel. I broke the nipple on the resonator though! Fuel pressure regulator looks clean and dry. No sign of leaks. I sprayed the MAF with MAF sensor cleaner, and that seemed to help a tiny bit, but really not sure. I just went outside and beat a little sand out of the air filter and really can't remember when it was last changed, so I'll get one tomorrow. I don't think any of the other codes will cause this terrible idle problem, so this is the one I'm focusing on. Would an exhaust leak where the main CAT was taken out cause this? The cat was cut out and gutted a couple of years ago and I put it back in with sections of pipe over the old pipe and clamps. I've noticed it's leaking a little. If it was an O2 sensor, would it be upstream or downstream? The downstream has the spark plug anti-foul trick and has not caused any problems or codes for a couple of years. Could this be somehow related to the P0455 and P0442 codes. Those have been popping up occasionally for a few months, but the P0172 is pretty new.
Thanks for all the help you give here.
 

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Sorry I missed your response. Sometimes the format here makes it difficult to catch all of the posts.

Does your scan tool read live data? It would be helpful to look at fuel trims and misfire counters. If you are having misfires the unburned fuel will be dumping into the exhaust. There could also be one or more injectors sticking. I don't think the rough running engine would be caused by the PCM making fuel adjustments. That's a normal function and you wouldn't notice anything unless there was a major imbalance that the PCM could not correct for.

Not positive about the exhaust leak downstream. I'm inclined to think it is not the source of the rough engine issue. The main input to the PCM is the upstream O2 Sensor. When was that last replaced?

P0455 and P0442 are strictly EVAP leak codes. Unless the purge valve, on the side of the engine, is stuck open those leaks should have no effect on the engine operation.
 

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Discussion Starter · #7 ·
I have limited live data. Yesterday the MAF was 4.2 g/s and the fuel trim was -21. The truck seems to run fine while driving down the road, but stumbles when I'm sitting at a traffic light and sometimes even shuts off. Several times a day now, I'm pulling over to check and erase codes. Finances are pretty tight right now, so I started praying that God would keep my truck running because I can't afford a costly repair. The next time I pulled up to a traffic light, I prepared to put it in neutral to baby it and keep it running, but it didn't act up. I looked down and saw where the check engine light was not on. It went off without me deleting codes!! I'll let you know what happens today.
Several years ago, the exhaust manifold was replaced with a header. The manifold was cracked in several places and came out in 3 pieces! The header came with the pre-cat and O2 sensor, so it's several years old. Also, a couple of times yesterday when I came to a red light, I put the truck in neutral when it started to act up and it actually idled up to around 2,000 RPM's by itself. It then threw a P0507 code.
Not sure what that was all about. I'll let you know how it runs and if codes come back.
Thanks for all your help buddy!!
 

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When I replace my air filter on my '05 3.5, I write the date on the side of the air filter with a black fine point sharpie, as I do with most filters on other vehicles and equipment. From time to time I rap the air filter on something, peek thru it at the sun, and roll with it till change time. Good luck with the codes.
 

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Discussion Starter · #9 ·
I used to to do that too, but this filter is black! I did find my spreadsheet that I keep on my vehicles and saw where it was replaced less than a year ago.
All codes are back. I did repair an exhaust leak today. I don't expect that to help any of the codes, but while working on that, I disconnected the battery for about an hour, maybe that'll help.
I fixed the exhaust leak because the now that the heat is here, I'm driving with windows closed and A/C on and the fumes in the cab of the truck were getting pretty bad.
I'm thinking I have a bad injector. Last 2 times I filled up the tank it was really hard to start. Usually when I get where I'm going it sits for hours before I crank it up again. so what ever excessive gas is in the cylinders, has time to evaporate. But shutting it off for just a few minutes to fill the tank, it doesn't want to start right back up. I'm not lookin forward to taking that intake manifold off! That looks like an all day job! But it will be good to replace the leaking valve cover gasket and I would like to take the plastic cover off the intake. I've seen pictures here of that removed and i think it looks pretty cool.
 

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When I replace my air filter on my '05 3.5, I write the date on the side of the air filter with a black fine point sharpie, as I do with most filters on other vehicles and equipment. From time to time I rap the air filter on something, peek thru it at the sun, and roll with it till change time. Good luck with the codes.
Thanks - this is very helpful
 

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Discussion Starter · #11 ·
Update. Got a new code today. P0102. Symptoms are rough idle and occasional shut off at idle. Fuel trim at idle is -22, but gets close to 0 once I get up to about 50 MPH. My scan tool always shows being in closed loop. Don't know if that's normal. MAF seems to be working with readings of around 4.2 at idle.
So, I've got a constant P0172 code and have recently added to it a P0102 code. Everything I've read about the P0102 code seems to be a nightmare of replacing MAF, with no success, then tracing down wiring issues, replacing BCM's and all sorts of other things without success.
 

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MAF: Assuming that you have already tried cleaning the sensor, you should be seeing 3-6 g/s at idle and 140 or more at 1-2 shift point. Some non-sensor issues that can contribute to a P0102: restricted/collapsed intake duct, loose intake duct clamps, misaligned intake duct or dirty air filter.
 

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Discussion Starter · #13 ·
Yeah, I've sprayed the MAF down twice. I thought an injector might be stuck, but that would throw a misfire code. My MAF reading is about 4.72 at idle. While driving, I've noticed that it goes way up, but haven't really been able to study it while driving. It's a pretty cheap hand-held thing. When it's acting up, the long term fuel trim is -21, but at about 50 MPH I glanced down and noticed it was at 0. It's been great today with no stumbling or issues at all. It's an off-and-in sort of thing. I never think to check fuel trims or anything else when it's running well. I'll check the basic intake items and replace the filter.
Thanks,
 

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I used to to do that too, but this filter is black! I did find my spreadsheet that I keep on my vehicles and saw where it was replaced less than a year ago.
All codes are back. I did repair an exhaust leak today. I don't expect that to help any of the codes, but while working on that, I disconnected the battery for about an hour, maybe that'll help.
I fixed the exhaust leak because the now that the heat is here, I'm driving with windows closed and A/C on and the fumes in the cab of the truck were getting pretty bad.
I'm thinking I have a bad injector. Last 2 times I filled up the tank it was really hard to start. Usually when I get where I'm going it sits for hours before I crank it up again. so what ever excessive gas is in the cylinders, has time to evaporate. But shutting it off for just a few minutes to fill the tank, it doesn't want to start right back up. I'm not lookin forward to taking that intake manifold off! That looks like an all day job! But it will be good to replace the leaking valve cover gasket and I would like to take the plastic cover off the intake. I've seen pictures here of that removed and i think it looks pretty cool.
The black fine point sharpie writes just fine on the side of the white filter element. Date, miles, and initials work for me.
 

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Discussion Starter · #16 ·
Looking over my maintenance records, I've got 85,000 miles on my spark plugs, and almost 60,000 on my air filter. Looks like it's time to spend a few bucks! These A/C Delco iridium plugs are getting a bit crusty looking. They're $10 each, but if they've lasted 85,000 miles, I'm good with that. In 1976, when I worked at a service station, we recommended to all of our customers that they needed points and plugs every year or 12,000 miles, whichever came first! That was standard procedure. But a tune-up on a V-8 ran $27.50. $17.50 of that was labor. That included hooking it up to the "SUN" tune-up machine and everything! Minimum wage was $2.35/hr, and I patched tires all day long for an average of $3 each. That included finding the leak, taking the tire off of the rim and inserting a "hot patch" on the inside of the tire. Those things were great!
 

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Discussion Starter · #17 ·
Erased codes, installed new A/C Delco iridium plugs and air filter, and so far it looks good. I ran it for about 10 minutes and hooked up my scan tool and the long term fuel trims were around -4. For weeks now the trims at idle have been around -22. I haven't gone for a long drive yet. It's hot here in Savannah! I worked back-to-back 10 hour days outside in the heat and the high was 98 degrees. I'm spending most of the day inside today, but had to get out a little and mess around with my truck though.
 

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Looking over my maintenance records, I've got 85,000 miles on my spark plugs, and almost 60,000 on my air filter. Looks like it's time to spend a few bucks! These A/C Delco iridium plugs are getting a bit crusty looking. They're $10 each, but if they've lasted 85,000 miles, I'm good with that. In 1976, when I worked at a service station, we recommended to all of our customers that they needed points and plugs every year or 12,000 miles, whichever came first! That was standard procedure. But a tune-up on a V-8 ran $27.50. $17.50 of that was labor. That included hooking it up to the "SUN" tune-up machine and everything! Minimum wage was $2.35/hr, and I patched tires all day long for an average of $3 each. That included finding the leak, taking the tire off of the rim and inserting a "hot patch" on the inside of the tire. Those things were great!
Man, I remember those days well. Chalk marked the tire where the valve stem was so I didn't mess up the balance when I remounted the tire.
Anytime I pull spark plugs, mowers or whatever, they get cleaned on the wire wheel end of my grinder, and gap checked. If wear looks good on them, I roll with them. Dab of anti seize on the threads, a smaller dab of dielectric grease on the plug wire end. I replace my 3.5 plugs at 100,000 miles, no issues. I have a set waiting for the 300K service, AC Delco Iridium. Air filter changes @ 50K. Fuel filter @ 35K, helps extend fuel pump life, mine has never been changed.
Noticed the other day the Driver Side Seat Bottom Slide Lever was broke off, no idea how that happened. They are on fleabay all day for around $8, but all black and right side only, I needed a gray one for the left side. AMZ had 'em for $12, just got it and put it on.
Overall they are great trucks, best wishes with the codes!
 
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