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Help on scanned codes on my Sierra


 
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Robin Hood
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Joined: 17 Jul 2000
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PostPosted: Fri Jul 25, 2014 1:05 pm    Post subject: Help on scanned codes on my Sierra Reply to specific post Reply with quote

Have a 05 Sierra with a 4.3 six that has become quite a disappointment to me. Bought it new, has 87,000 miles on it and it has serious rust issues.
Now I have to get it inspected with a pile of codes on it that I don't know what to do with them. Would appreciate any insight you are willing to lend.

Codes are: P0300, P0420, P0430, P0138, P0158, and P0171.

Only thing I know is there is a GM TSB on the distributor "vent" screens (I will yank them tomorrow, as per TSB, and install new OEM cap and rotor. Plugs and wires were changed about 10,000 miles ago. The last code - P0171 makes me wonder if the thermostat is the culprit since the truck seems to run cooler than it did when new. I just don't know.

Would appreciate any help you can give.

Thanks.
 
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glennster
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PostPosted: Fri Jul 25, 2014 1:26 pm    Post subject: Re: Help on scanned codes on my Sierra Reply to specific post Reply with quote

my o6 4.3 wt tossed similiar codes. check your 02 sensoers, the scanner should indicate which bank. bank 1 lt side, bank2 passenger side. my lt 02 sensor after the cat was bad. check for a blown fuse in the panel also. sometimes the fuse will pop too with a bad sensor. do you have a scan tool that can clear the codes?
 
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Robin Hood
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PostPosted: Fri Jul 25, 2014 1:29 pm    Post subject: Re: Help on scanned codes on my Sierra Reply to specific post Reply with quote

Yes I cleared the codes. It has been running rough for quite some time. I am hoping after I change the cap and rotor, it might clear.
 
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glennster
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PostPosted: Fri Jul 25, 2014 1:49 pm    Post subject: Re: Help on scanned codes on my Sierra Reply to specific post Reply with quote

look here for the 0158 code
poke here

 
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Robin Hood
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PostPosted: Fri Jul 25, 2014 4:44 pm    Post subject: Re: Help on scanned codes on my Sierra Reply to specific post Reply with quote

Thank you for your help. It doesn't sound like I am going to get away from this for cheap. Oh well.
 
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jimg.allentown
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PostPosted: Fri Jul 25, 2014 4:52 pm    Post subject: Re: Help on scanned codes on my Sierra Reply to specific post Reply with quote

Just off the top of my head, the P0420 is a catalytic converter operating below efficiency threshold. P0171 and P0158 are mixture codes.

IMHO, with that many codes, you need to start with the FIRST code output, and solve that one, clear the rest, and drive it until the MIL light comes on again. Then repeat the procedure until all of the codes stop recurring. Usually, one problem starts, and ends up throwing things out of kilter until it generates a bunch more "bogus" codes.
Good luck.
 
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Bob
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PostPosted: Fri Jul 25, 2014 9:14 pm    Post subject: Re: Help on scanned codes on my Sierra Reply to specific post Reply with quote

PO300 = misfire not linked to just one cylinder.

You need to solve that code FIRST before even DREAMING about any codes pertaining to the exhaust oxygen sensors.

I agree with installing a new OEM cap and rotor, but don"t worry about ripping out the distributor vent screens just yet.

Get it running without a misfire, and THEN worry about doing PM to prevent the problem from returning.
 
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4play
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PostPosted: Fri Jul 25, 2014 9:48 pm    Post subject: Re: Help on scanned codes on my Sierra Reply to specific post Reply with quote

P0171 would not generate from a thermostat problem, incidentally there are certain codes that can set due to engine temp/thermostat concerns, especially when they are stuck op and running too cool.

P0171 means the engine (bank 1) is running too lean, lean to the point where the PCM attempted to add extra fuel and reached its limit of compensation and its still too lean. Vacuum leaks (vac lines/hoses, intake gasket etc are usually the culprit but a fuel supply/delivery problem often cause problems too among a few other things.

The p0138,p0158 are for the rear oxygen sensors behind the catalytic converters (after cat) indicating excessive voltage. Possible causes are faulty cats, shorted/melted sensors or wiring.

The p0420,p0430 codes generate from the rear sensors too. These codes trip when the PCM sees the rear sensors mimicking the front sensor switch rate which means the cats are not cleaning the exhaust emissions to a specific level. Most likely cause is the catalytic converters. Often times driving a vehicle with excessive misfiring can burn out the cats from excessive heat generated from unburned fuel.

The p0300 is typical when an engine simply runs rough and not on a particular cylinder or random. Many things can cause this from typical tune up items, sensors-ignition, mechanical problems, fuel problems, sensors, among the same things listed above with p0171. Since you are taking the dist cap off, verify the rotor or dist shaft does not have excessive play when turning back/forth. I have seen a few of these trucks with worn gears on the dist, also some worn dist shafts too.

So, basically I would try to look into the P0171 and P0300 running problem first, the other codes maybe related to the running problem from these two codes.

Sorry for the long post, I dont want to add more right now but if you check some stuff out then repost and maybe we can help narrow things down.
 
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George Marsh
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PostPosted: Sun Jul 27, 2014 1:04 pm    Post subject: Re: Help on scanned codes on my Sierra Reply to specific post Reply with quote

I'vw had many issues with the distrubutor on my 2007 GMC 4.3L, Delco dist. So I went to Auto Zone and bought a 5 year distrubutor. Well it went bad just like the OEM delco. Took it back and they replaced it free.

Someone on YT suggested I put a coat of grease on distrubutor to keep the crap and moisture out. So far it's worked. I'm lucky to get 20-30k out of my distributors. That's why I gave up on delco's. Had the same problem with my 95 GMC. Every time I had distrubutor failure, it was extremely humid, raining, or condensation due to a rapid temp change.

As for rust, I took my 2007 GMC to Z-tech the day I bought it. Z-tech for under coat, sprayed bed liner and a wax job. Best money spent. No signs of rust. They put a lot of salt on roads in winter too.

I somewhat wished I had gotten the V8 engine. It has a distributor-less ignition and variable valve timing, I think that's what it's called. Where the v8 can become a 6 cylinder if you don't need the power.

George
 
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