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2006 chevy trailblazer_lt
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Discussion Starter #1
My wife's 2006 Trailblazer has about 110k on it. It has been well maintained. At about 50K I replaced the fuel pump because the fuel gauge was no longer working. Now I'm back to the same problem - suspect I replaced with another faulty pump. Normally you turn the key let go and the vehicle cranks till it starts. With the faulty fuel gauge, you have to hold the key forward until the engine starts. Due to her/our programmed brains, we often attempted to start the truck and release the key before it actually started. Check engine light would come on. For some time now, we have been using the trip odometer to keep track of the gas level. I finally decided to have the light checked a few days ago. PO131, POO30, PO135, PO300, PO463, PO304. The codes were cleared and today I'm left with PO135 and PO304. The truck runs and drives fine. I think I get the PO135 might be 02 sensor but I'm a bit perplexed on the PO304. The truck runs well with no noticeable miss. I would appreciate any guidance and yes I have to get the fuel gauge issue fixed soon - It's wearing on my wife.
 

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2004 chevy trailblazer_lt
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267 Posts
First off you have a problem with the upstream O2 sensor or sensor circuit. The P0131 code is telling you that the O2 sensor has a low voltage condition caused by either a wiring problem or a bad O2 sensor. The P0135 code is telling you there is a problem with the O2 sensor's heating element circuit. The P0030 is another code telling you there is a problem with the O2 sensor's heating element circuit. First, make sure the wiring harness and connector to the O2 sensor is intact and not falling apart. If all looks well and the voltages check out, you just might want to replace the O2 sensor with either an ACDelco OEM or a Denso O2 sensor.

Second, the P0300 is a code for a random misfire and P0304 is a code for a cylinder 4 misfire. Could be spark plug, ignition coil, fuel injector, cylinder compression, a bad electrical connection to the #4 ignition coil or #4 fuel injector. You need to troubleshoot it. Question, when was the last time you changed the spark plugs?

The P0463 code is for the fuel level signal that is going above 5 VDC for a specific amount of time. It could be a defective fuel level sending unit on the fuel pump assembly or a bad electrical connection somewhere between the fuel pump assembly and the PCM. Have you checked the fuel pump pressure to see if it is low? Have you examined the wiring connectors to the fuel pump assembly? If you do determine that the fuel pump is bad, then replace it with either an ACDelco OEM or a Delphi fuel pump assembly. Yes, it will cost more, but it will likely last a heck of a lot longer than an inexpensive generic pump with questionable quality.

Good luck!
 

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2006 chevy trailblazer_lt
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Discussion Starter #3
Excellent info - thank you so much! Plugs were changed around 80K with AC Delco's. The old plugs looked almost like they had no wear. I did the last pump/sending unit myself without a lift. It was a real PIA dropping the tank and I dread the thought of attempting it again. I do remember that the wiring harness snap was broke in the process and to hold the connectors together I wrapped in electrical tape. Always wondered if maybe this wasn't part of the current gauge problem. The harness was so short it gave me almost no room to disconnect it while laying underneath the truck. Might be a job for a pro next time around.
 

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2006 chevy trailblazer_lt
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Discussion Starter #4
Just a quick follow-up. I tried to get the O2 sensor out myself and broke one cheap ratchet and a socket designed specifically for O2 sensors. Probably needed heat which I had but I decided to raise the white flag and took it to a shop. I also asked them to check out the cylinder misfire and they sold me FTPK20 Fuel System Cleaner. Dumped one can in a vacuum line and the other in the tank. All codes are gone and seem to be running well so I suspect just a slightly clogged fuel injector.
 
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