Code 300 is for a random miss.
172 and 175 are for the same problem - 172 is for a rich fuel mixture bank one and 175 is for the fuel mixture too rich on bank two.
Code 143 is for a rich mixture for sensor number 3.
All of the codes could be connected to a leaking injector or other fuel problem. Very seldom are all of the O2 sensors faulty at the same time.
SOURCE: codes po172 and po175 too rich mixture
easy one.. when ever you have codes and want to know what they are..visit.. www.bestdirectorysolutions.com on the home page.. left side, scroll down and click on trouble codes... good luck sir
SOURCE: have a 1999 Chevy Tahoe,
* p0172 bank 1 rich. If you have access to a scan tool, I would check the fuel trim and see if engine is running rich all the time. In Chevy, if both banks are too lean or too rich, usually the cause is the Mass Air Flow sensor being dirty.
* P0420 The PCM copares switch rates between the front O2 sensors and the downstream catalyst moniters. The catylist moniters are often mistaken as O2 sensors, and they are, but that is not their job, or what they are called. By comparing the switch rates between the front (before cat) and rear (downstream of cat) the PCM knows if the cat is affecting the exaust, and how much it is affecting the exaust. If it sees little or no effect o the exaust gases that have passed through the cat, then it decides that the cat is not working anymore, and sets a P0420, bank 1 it is. To check this yourself, you will need to bring up data stream on your scanner, watch the upstream and downstream O2 parameters and see if they are following each other closely. If the cat is working right, you should see a fairly rapid switch rate, probably 5 or 6 times a minute on the front O2, but almost a flat line just above .5 volts on the rear. If the rear is switching often you proabably need a catalytic converter. Most likely related to the P0172 code above.
* P0300 multi misfire probable cause. Fuel injectors always seem to get the blame for this one since the there is only a lean condition to one side of the engine.
The fuel injectors on these trucks really have one problem, the poppet nozzles at the end. They can stick either open or closed. If they are stuck closed, then servicing the system will clear up the problem (I recommend that they use the 'top engine cleaner' over anything else). However, if they are stuck OPEN, then no amount of cleaning or servicing will fix the problem unless the nozzles are replaced.
Here is a TSB link to the GM's upgrade from the SCPI to MPI system for your truck. http://members.shaw.ca/betterthanyoutoo/Sticking%20Poppet.htm
Here is also a link to the conversion being done on a 4.3 V6 vortec with the same issues your having. http://www.s10forum.com/forum/f107/scpi-to-mfi-upgrade-kit-324166/
Good luck and try using fuel injector cleaner first to address the issue, Lucas fuel injector cleaner is great for the price for how much you get for it. Just follow the instructions on the bottle and you should be good for a month of injector cleaner when you fill up the gas tank.
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SOURCE: Service Engine Light
have u checked/ replaced your o2 sensors since you have owned the vehicle?
SOURCE: po171 po172 po174 po175 ???
If the fuel pressure was low enough to give lean codes then u would have a loss of power that you would easily notice, you say you checked for vacuum leaks, did you use a can of carb spray or a bottle of propane? it only takes a very small leak to trigger the codes, spray carb spray around the intake area, see if the engine sound changes, this will indicate a leak,
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I have not changed o2 sensors yet. The truck runs fine it just pops the codes. Im kinda thinking that a dirty mass air flow makes sense. If its making it run rich it would cause the other codes to come up.
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