Postby smj999smj » Thu Dec 29, 2016 1:51 pm
Why one place pulled one code and the other, two codes, I cannot tell you. The P0420/P0430 codes are fairly common once these vehicles get some miles on them. Usually, an oxygen sensor will trigger a trouble code if it is faulty. The factory service manual provides some testing procedures for oxygen sensors, usually a component test to check resistance with the sensor and operation testing, which would require a scantool to view datastream info from the ECM. The upstream sensors are actually air/fuel ratio sensors, which look like oxygen sensors, but operate a bit different. The rear sensors are actually oxygen sensors and are only used for monitoring the upstream catalytic converter efficiency. More often than not, it is the upper catalytic converter that fails (becomes inefficient at breaking down the exhaust emissions) that triggers the code. I've had good luck with Walker direct-fit catalytic converters, but, in some states, converters need to be C.A.R.B. compliant to pass state emissions.
P0850 is not unheard of in these vehicles, as well, but is a less common code. It is for the PNP (park/neutral position) switch, which is part of the transmission's TCM/valve body assembly. The usually fix is replacing the TCM/Valve body assembly, which will probably fall in the $1500-$1800 range with parts and labor.