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Dave Nova
Dave Nova, Chevrolet Technician
Category: Chevy
Satisfied Customers: 19451
Experience:  ASE Master Certification. GM World Class Certification
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2000 s10: drove..50 miles pcm will not do any self come

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2000 s10 truck 2.2 auto codes po178 and 179 fuel composition sensor, cleared codes and drove 50 miles pcm will not do any self test and complete monitors, if you cycle ignition codes come back but 200mi later still no monitors complete? does the pcm need to pass fuel comp sensor test before it will continue to test others or is there a problem with pcm?
There are certain monitors that will not run with these dtcs set. Once the problem is repaired and the codes are cleared, the monitors should all run successfully. Before replacing the fuel composition sensor, try flushing it out. I had one that got a tiny piece of trash in it that I was able to flush out by disconnecting the lines and using brake cleaner spray to flow through the sensor backwards. If this doesn't work, of course the sensor will need to be replaced.
Customer: replied 6 years ago.
ok, what I did was clear codes, my book said the sensor won't be tested untill the 2nd key cycle so I cleared the codes and drove it all over the place without shutting it off tried to do obd drive cycle but sill no monitors complete? and if you shut truck off and restart you drive 200ft and one of the codes comes back. I heard that someone is selling a bypass sensor for the fuel comp sensor on ebay but if truck still won't run monitor test?? I'll try to clean it out and retest, Thanks, John
This code can set on the first drive cycle, the light turns on the second consecutive drive cycle that the code sets.
Customer: replied 6 years ago.
Hi, I have the sensor out to clean right now.. but in your last answer, as I said I drove truck alot with scanner on and had no codes and no set monitors? codes only set after key cycle?
They will set as a pending code on the first drive cycle, then once the fault is recognized a second time, it will set as a hard code.
Customer: replied 6 years ago.
Hi Dave, well I cleaned the sensor and check engine light sill comes on after I shut it off and restart it? I think I need a new sensor? but what I needed to know seeing I am in MA.. this truck needs to show that it has completed monitors all but 2 to pass state inspection and it won't do any? you can drive this truck to CA. on first key cycle and check engine light will not come on but you won't have 1 completed monitor? If you restart you will get codes and you can drive back from CA and it sill won't set any monitors. Does the pcm need to know the fuel composition sensor is working correctly before it test the other monitors? thanks, John
It does need to know the fuel composition sensor is working correctly before completing the other monitors. If the computer does not know what type of fuel is in the system (gasoline or E85) it cannot correctly determine the air/fuel ratio and know whether the engine is rich or lean. Therefore, it will not run any of the other monitors. Once the sensor is replaced, the other monitors will run.
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