p0125 = insufficient coolant temp for closed loop fuel control
p0401 = exhaust gas recirculation flow insufficient detected
p0420 = catalyst system bank 1 efficiency below threshold|||you asked for more help
wow you sure have done a lot i wish you would have brought it into my shop i think i could have found the real problem without all the expense
what your describing is classic symptoms of a head gasket gone bad it will set all the codes you have mentioned and give you all the problems as well
2 ways to test
1 fill radiator leave the radiator cap off start car look for antifreeze to gush out of radiator or steady stream of bubbles while the engine is cold
2 there is a chemical test that can be done as well
it wont necessarily have coolant in the oil as the part of the gasket that fails is between the piston and the nearest coolant passageways sealers wont work here you must pull the heads and have them machined
i have done this job many times on that model as most people don't fill the radiator properly
hope this helps
po125 change the thermostat
po401 clean pipes that go to egr valve remove valve to clean inside also can be broken vacuum lines that go to it
po420 clear codes after other codes fixed to see if it come back on Thain you will need a scan tool that shows live data to test further|||Once your engine coolant temperature is verified to be about 200 degrees F at hot engine idle using a non contact temperature gun pointed at the thermostat housing, then check the Engine Coolant Temperature (ECT) sensor to make sure it's telling the computer that the engine coolant is hot. The EGR valve and EGR intake manifold passageways need to be cleaned of carbon deposits that are restricting the flow of exhaust gases back into the intake manifold. You can add a carbon cleaner to your fuel tank to help the problem.
http://www.autozone.com/az/cds/en_us/090鈥?/a>|||sounds like the O2 sensor is screwing up to me.
the bad thing is it could be either one that is messing up which will cause the engine to run different to try and fix the problems it is reading|||Hi oosmurfe: Code p0125 This has to do with engine temperature .. If your car is not getting up to operating temperature reasonably quickly, replace the engine thermostat. I would try this first ..
Code p0401 It is part of the vehicle emmissions system, and is used to reduce combustion temperature . Either the sensor on your EGR is bad, or the valve itself if stuck. You will need a pro to help with this EGRs are tricky ..
Code p0420 If the car has a lot of mileage .. It's probably the catalytic converter. They can be very expensive . So get very good advice about your problem .. I hope this is helpful .