I have been having problems for about 6 months with this car. So far, we have replaced the 02 sensor (3 times) the radiator, the catalytic convertor, the Ignition module, the fuel pressure pump, the filters (gas etc) and several other smaller parts. The spark plugs are good, as are the wires etc to everything. Before we replaced the ignition module, I was getting P0300 and P0420. Once we replaced the ICM p0300 code went away. P0420 also went off for a day. Went to have it smogged, and it failed. They said that the reading should be 100, but mine was 330! Before we replaced the ICM, it did run rich, has loss of power etc (all the problems related to bad ICM - which seemed to go away for that one glorious day.) My father in law is a mechanic, but we have replaced almost everything on this car except a whole new engine... At a loss as to what to replace next! Could the Catalytic converter have gone bad again because of the bad ICM?
Code p 0420 refers to cat converter system bank 1---efficiency below threshold====causes ---cat converter---wiring---HO2S (heated oxygen sensor, the one in the exhaust manifold before the cat converter)
code p 0300 is random misfires
I would suggest changing the HO2S as it reports to the ECM on exhaust content so that the ECM can adjust the air/fuel ratio
so it is logical that if that unit is not reporting correctly, the cat converter may be having trouble burning off the gasses correctly
The oxygen sensor(O2S) reads the results of the cat converter operation and helps fine tune the ECM settings
SOURCE: 2002 Buick Century Code P0420
Sounds as if yoou are actually having a fuel system problem.You need to rreplace the fuel filter and then check the fuel pressure. You should have around 50 psi. If the fuel filter stops up it will cause the exhast to starve for fuel and can damage a catalyst converter. You can get the fuel filter for about 15 dollars at any local parts house.
SOURCE: 1993 Buick Century Custom 3.3L Runs Rich, Ruff at idle; 10MPG
Check the fuel filter, it might be clogged.
SOURCE: 12 codes; 90174, p0171, p0175,p0300,p0301, p0302,
90174 (guessing it should be p0174 = system too lean)
92198 (guessing it should be p2198 = Oxygen Sensor Stuck Too Lean / Rich)
p0171, p0175 = system too lean (usually related to MAF Sensor)
p0301= Cylinder 1 Misfire Detected (Coil related most likely)
p0302 = Cylinder 2 Misfire Detected (Coil related most likely)
p0303 = Cylinder 3 Misfire Detected (Coil related most likely)
p0316 = Cylinder Misfire Detected (Coil related most likely)
p0420 = Catalyst System Efficiency Below Threshold
p2195, p2196 = Oxygen Sensor Stuck Too Lean / Rich (most likely the rubber hose from valve cover to throttle body
You may want to have your MAF changed, Coils changed, and your O2 Sensor checked. Also any one of those faults can also trigger another fault. I.E your O2 sensor could be could, but since it's misfiring, it's being triggered because the exhaust gases aren't what it should be. Hope this helps
Testimonial: "Thanks, you was very helpful. Since I got the codes the engine lock up on me. The car light comes on but the car would not start. I had it towed. "
SOURCE: my 2005 pontiac grand prix has a bad misfire and
you have a cracked vaccum hose going to your fuel regulator and purge valve.
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