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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 07-24-2006, 04:44 PM
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Got code P0172

On my way home form work today the service engine light came on. I stopped by Advance Auto and read the code and it is P0172 System Too Rich(Bank 1). My first thought ws bad 02 sensor. Then I rememberd that I had my battery disconnected for a while yesterday. Could this be why I got the code? I reset it and it didn't come back between Advance Auto and here(less than 5min drive). I did a search and didn't find much info about this code.
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  #2  
Old 07-24-2006, 10:18 PM
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DTC 0172 sets when the engine is in closed loop and the PCM detects an excessively rich fuel condition. While the O2 sensor, EVAP system and the fuel injectors should be tested, there are a few basics to immediately consider. First, contaminated fuel (water or alcohol) can be the culprit. It plays havoc with fuel trim. Second, obstructions in the air intake system should be checked. The air intake ducts and the throttle body should be examined for any blocked or dirty conditions (fuel metering may be correct, but anticipated air flow is not). I don't suspect disconnection of your battery is responsible. Any long term fuel trim values in the PCM are coarse adjustments. The short term fuel trim (fine adjustsments) are accomplished through the PCM's reading of the O2 sensor's flucuating voltage signal. That is not a stored value but varies as soon as the engine goes into closed loop operation.
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Old 07-24-2006, 10:43 PM
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Old 07-24-2006, 10:53 PM
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Vince, I wouldn't sweat it. You reset it & it didn't come back. The 4.2L runs a bit rich by nature so it doesn't take much to throw it over the edge. Running in open loop from the battery disconnection probably mixed her up for a bit. IMO, GM added the MAF sensor to the 2006's to help prevent this.

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Old 07-25-2006, 07:58 AM
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Thanks for all the replies.

The light didn't come back on during the drive in to work, so hopefully everything is all right.
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Old 07-25-2006, 09:44 AM
Fast68Camaro Fast68Camaro is offline
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Maybe this bit of insight will help, though I hope it is not the problem. I had this same code on a 1996 Monte Carlo Z34. I replaced both O2 sensors (a real pain on a DOHC car) and the code came back. Took it to the stealership who said "no, no, no, it's the O2 sensors, your partshouse brand is just not good enough for your car's computer". So I let them replace the sensors, light came on while driving home.

So back to the stealership. "Well, we can hear the plug wires arching, so its the wires and plugs". So I negotiate a credit for the O2 sensors and labor and let them replace the wires and plugs (again, not a fun job on the DOHC engine). Light comes on again after a day or two of driving.

So, by this time I'm getting pretty fed up with this crap, and the stealership finally gets a GM regional guy to come in. Push comes to shove, it was the injectors and they had to replace them all. $1,200 for the injectors, but I shouldn't complain since I got new wire, plugs, and O2 sensors for free right? Just 3 or 4 times losing use of my car with no rental coverage.

Hope your code turns out to be a fluke.
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Old 07-25-2006, 10:15 AM
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Quote:
Originally Posted by Fast68Camaro
Maybe this bit of insight will help, though I hope it is not the problem. I had this same code on a 1996 Monte Carlo Z34. I replaced both O2 sensors (a real pain on a DOHC car) and the code came back. Took it to the stealership who said "no, no, no, it's the O2 sensors, your partshouse brand is just not good enough for your car's computer". So I let them replace the sensors, light came on while driving home.

So back to the stealership. "Well, we can hear the plug wires arching, so its the wires and plugs". So I negotiate a credit for the O2 sensors and labor and let them replace the wires and plugs (again, not a fun job on the DOHC engine). Light comes on again after a day or two of driving.

So, by this time I'm getting pretty fed up with this crap, and the stealership finally gets a GM regional guy to come in. Push comes to shove, it was the injectors and they had to replace them all. $1,200 for the injectors, but I shouldn't complain since I got new wire, plugs, and O2 sensors for free right? Just 3 or 4 times losing use of my car with no rental coverage.

Hope your code turns out to be a fluke.
Hopefully it sis a fluke. I really don't want to have to go through the dealer "troubleshooting" the problem. The dealers seem to do more part swapping than troubleshooting. The good news is if the code does come back I have ~2000mi left on the warranty.
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Old 07-25-2006, 10:46 AM
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Quote:
Originally Posted by Vince
Hopefully it sis a fluke. I really don't want to have to go through the dealer "troubleshooting" the problem. The dealers seem to do more part swapping than troubleshooting. The good news is if the code does come back I have ~2000mi left on the warranty.
You might want to consider an extended warranty while you still can get one.
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Old 07-25-2006, 12:28 PM
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Originally Posted by Envoy Fan
You might want to consider an extended warranty while you still can get one.

Yeah, i thought about it. I think they charge an absurd amount of money when you buy the warranty with that many miles on the vehicle. I might look in to it some more since I plan on keeping it at least 4 more years.
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Old 07-25-2006, 01:05 PM
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Quote:
Originally Posted by Fast68Camaro
.... it was the injectors and they had to replace them all. $1,200 for the injectors, but I shouldn't complain since I got new wire, plugs, and O2 sensors for free right? Just 3 or 4 times losing use of my car with no rental coverage.

Hope your code turns out to be a fluke.
I can almost bet it wasnt the injectors themselves on that Z34 if you had a lean code. It was probably a vac leak around an injector (bad O-ring). A dirty MAF sensor would screw up the fuel trim on the GM DOHC V6's as well. That dealership got lucky as they threw enough new parts on her to make the SES light go away. Big thing to remember is to NOT replace an O2 sensor based on lean or rich code! The O2 sensor is telling you something is not right upstream.

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