Chevy Impala, check engine light on

gullythumper

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Make
chevy
Model
impala
Year
2003
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117,731
Engine
V6
2003 impala. check engine light just came on. Local auto store put the 'puter on it and it said : Fault is P0171, something like bank 1 running lean. Their cheapy reader didn't elaborate as to what part is bad. Can anyone shed some light on this?
 

grcauto

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Bank one is lean. Exhaust leak prior to the cat?
 

mhamilton85

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No way to tell what part is bad without actual diagnostic work. The code gives you a starting point only. Could be a bad O2 stuck low, or if actually a lean condition it could be a leak anywhere between the MAF and the intake port(s). If nothing is obviously broken/cracked/disconnected from a visual inspection under the hood, the quickest way to identify that would be a smoke test--recommend you take the car to a shop if you don't have a way to verify fuel trims.
 

nickb2

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Here are a few hints.

If it would have coded both banks, we would lean, pun intended, towards a fuel "deprived" system strategy, such as a intake boot leak, weak fuel pump etc. But since it is coding only on one bank, look for a vac leak at intake gasket for that bank or an exhaust leak on that side(bank). .
 
Last edited:

NickD

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Guys trying to sell me auto warranty, tell me a check engine light on can cost me thousands of dollars.

Lean can mean one of two things, excess air or a deficiency of fuel, kid had a Pontiac close to your year, remember when Pontiac's use to be Pontiac's and Chevy's were Chevy's, now you can't tell the difference between a Chevy or a Cadillac.

His problem was a bad gasket for the manifold pressure sensor one look under the hood, could hear it suck air. Had a tube of Permatex gasket maker, squeezed that around the sensor, reset the code and saved thousands of dollars.
 

nickb2

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His problem was a bad gasket for the manifold pressure sensor one look under the hood, could hear it suck air. Had a tube of Permatex gasket maker, squeezed that around the sensor, reset the code and saved thousands of dollars.
I put that shyte on everything. :beer::beer:


 

NickD

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Ha, if shyt works why not? Only way to get a new gasket was to buy a new manifold pressure gauge.

Another friend paid $1,500.00 to a shop with the same code and rough running engine, replaced this and that, but didn't cure the problem. His was loose intake manifold bolts, two minutes later problem went away.

This is another common problem with this engine.


Plastic intake manifold, not bad on a straight four or six, but has a different coefficient of expansion than cast iron or aluminum so develops cracks squeezed in between two heads.

Never was a problem when the entire engine was cast iron, claim they are saving weight, many people have more on their gut than the weight that is saved, key reason for these changes, a heck of a lot cheaper to manufacture, but sure can't tell this from the replacement cost. 700 degree F as opposed to 2,500 and no machining afterwards.

As an engineer have to do what the bean counters want or you won't have a job.
 

gullythumper

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Guys, I appologize for not responding sooner. Things have been real hectic around here. Anyhow, I took the car tomy mechanic and he put his good analyzer on it. Nothing showed bad. It said the car was running fines. He suggested that I may have gotten a bit of water in the fuel. So, at his suggestion, I put a can of dry gas in it, pulled the battery cable to re-set the computer, and the light has not come on since. Keeping my fingers crossed that it is cured. I guess time will tell. Thanks for all the responses
 

gullythumper

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Well, the damn thing came back on, and this time, dry gas and trying a reset by removing the + battery terminal didn't reset the computer. Car still starts easy, runs smooth at all rpm's, and makes no unusual noises under the hood. It goes back to my mechanic sometime in Feb. I'm hoping he can do that smoke test. I personally can't find anything, and know of nothing else I can try easily.
 

NickD

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Ever since OBD II starting model year code is stored in EEROM that does not lose its memory when the battery or voltage is removed. A lot like an SD chip in your digital camera or USB stick in your computer. Vehicle is 17 years old, most claim that memory is only good for ten years.

ECU or PCM, that computer thingy has to be in an airtight case not letting any moisture getting in that can leak off code.

88 Supra and any OBD I vehicle prior to 1996 has the key code burnt into the chip,that will never change. Has what is called open loop mode before the vehicle warms up that learns from closed loop mode, this is stored in power only read only memory and that is lost if you disconnect the battery.

In my car, adjusted all the sensors to read in the exact center of the specifications, so when the battery was disconnected, had nothing to learn.

Back then is cost 89 cent to burn a ROM chip including the chip, but the EPA and marketing insisted using EEROM that can be reflashed over the brand new internet to save mailing our new PROM chips, that;s permanent read only memory. If the software was not right. Actually with EEPROM programmers became more sloppy.

If out of warranty and you need a reflash can take a kid an hour to find the code according to your VIN on a computer, load it into his laptop, plug that into your diagnostic connector that can take an hour at 95 bucks per hour. New vehicles are using WiFi.

Field effect transistors where the code is stored do get leaky over time, should follow Obama's advice and received cash for clunkers, wants this old stuff off the road, sorry collectors.

Can't argue with the EPA. Ha, as a kid could pick up a large V-8 from a junk yard for like 60 bucks, get an adapter from Warshawski's in like a 48 Plymouth or Ford for another 50 bucks, and leave spoiled brat rich kids in the dust driving their daddies new vehicles. Only 6-8 wires between the dash and engine, today thousands.

Even back in the 70's was using a minimum of 16 AWG wire for a one ampere light bulb because it was more robust, today you will find lots of 30-36 AWG wire interfacing computers, don't look at it too hard, will break it.
 

billr

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If your mechanic can not test for exhaust leaks, like a smoke test, then you need a new mechanic...
 

Mobile Dan

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This is something easy to find, but also easy to miss...vacuum hose cracked at rear of intake manifold (windshield side) sets a lean code, but engine runs (almost) normal. This applies to 3.8 engine only.
 

billr

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I have never had to use smoke, just coupled a leaf-blower tight to the tailpipe and felt around the exhaust piping for a breeze coming out. Engine off and exhaust all cold, of course. The "smoke" is very similar, but you don't have to feel for the breeze, just look for the smoke; much quicker, easier, and more thorough. I think there are commercial smoke squibs/tablets that can be burned to produce smoke for ingesting into the leaf-blower inlet, but burning a little oil in a pan should do it too.
 
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