CODE PO171AND PO174 1996 CHEVY ASTRO

SOURCE: O2 sensor problem

I have a 97 gmc sierra .This truck is the same as the chevy ok.Its a 350 5.7 liter 4x4 Z71.I took it to auto zone which was my first mistake.They put it the scanner and said bad O2 sensor.Ok so which one is it i said.They dont know.Well there four (4) O2 sensors in this truck i hope you know that.I had to replace all four of them before i had to take it to a real shop.It seems the fuel pump i replaced a week earlier with an auto zone fuel pump was bad.Ive changed my feul pump 4 times now and have 235000 miles on still running.You need to get your fuel pressure checked.It should be 65 psi to start it and 55 psi to run it.If the pressures are good it could be a different O2 sensor or maybe the mass air flow senor.My last option would be the fuel pressure regulator because it seems to be a waste of time and money.I would get that fuel pressue checked first.Good luck.

anwar alkhaldi

• 197 Answers
• Posted on Mar 14, 2009

SOURCE: 1998 Chevy s10 4 cylinder running rough

1- check there is spark come from spark wires
2- check the fire timing by looking for every wire in the right place
3- check there is injector signl
4- check for any vacuom leak
5- try to clean the MAF by brake and parts cleaner
6- try to reset all the code and see what will come after that

SOURCE: Have a 2003 Chevy Impala. Check engine light

Bank 1 is the rear O2 sensor, but experience says to change both. The front one is right behind the engine in the middle of the engine compartment. The rear O2 sensor is on the top of the exhaust pipe, just behind the catalytic converter. But the same code that shows it is the O2 sensor (which is P0420), is the same code for the catalytic converter, or a vacuum leak. Make sure if you do change the catalytic converter, ensure that the new one is OBD-2 compliant. And the vacuum leak could possibly come from the manifold gasket. Let me know what the problem was!

SOURCE: 98 Astro Van,when warm hesitating, stalling

WELL YOU CHANGED ALMOST EVERY THING EXCEPT IGNITION CONTROL MODULE........

SOURCE: Pulled code p0420 on 99 chevy astro, 2wd, v6

from what i am finding the code means o2 sensors. they recommend replacing them and if this does not work than replacing the cat converter

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

causes

A code P0420 may mean that one or more of the following has happened:

• Leaded fuel was used where unleaded was called for
• An oxygen sensor is not reading (functioning) properly
• The engine coolant temperature sensor is not working properly
• Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
• Retarded spark timing
• The oxygen sensors in front and behind the converter are reporting too similar of readings

• Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
• Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
• Inspect the downstream heated oxygen sensor (HO2), replace if necessary
• Replace the catalytic converter