PO420 2003 Vue

[brian1973]

Hello all, hopefully I am posting in the right section.

I have a 2003 saturn vue FWD 4cyl 5 speed manual trans. It keeps setting off the SES light and the code PO420 comes up, I have replaced the catalytic convertor (saturn recommendation), the rear O2 sensor (local garage recommendation) and fuel filter. I am out of ideas on what may be causing this. Before replacing the fuel filter the engine would lose power and sputter and misfire, since replacing the fuel filter there was no loss of power when the code appeared. I have access to chiltons online and they give a few other possible causes like excessive oil usage which I can not verify since this is my wifes car and I have been working out of state for a while, my father in law has been the one doing the repairs, he and I are both diesel mechanics, he has over 35yrs experience with trucks and I have 15yrs on construction/heavy equipment.

[far2grumpy]

Hello all, hopefully I am posting in the right section.

I have a 2003 saturn vue FWD 4cyl 5 speed manual trans. It keeps setting off the SES light and the code PO420 comes up, I have replaced the catalytic convertor (saturn recommendation), the rear O2 sensor (local garage recommendation) and fuel filter. I am out of ideas on what may be causing this. Before replacing the fuel filter the engine would lose power and sputter and misfire, since replacing the fuel filter there was no loss of power when the code appeared. I have access to chiltons online and they give a few other possible causes like excessive oil usage which I can not verify since this is my wifes car and I have been working out of state for a while, my father in law has been the one doing the repairs, he and I are both diesel mechanics, he has over 35yrs experience with trucks and I have 15yrs on construction/heavy equipment.

Brian ... I've attached DTC P0420 explanation from Saturn service manual ... I hope the second cat is OK.

[brian1973]

Ok update here.. Replaced spark plugs and code went away.. yay.

Now there is another problem, when it gets down to a 1/4 tank of fuel it throws a PO172 code. I am guessing the fuel pump, maybe even the cap??

[RCH]

Ok update here.. Replaced spark plugs and code went away.. yay.

Now there is another problem, when it gets down to a 1/4 tank of fuel it throws a PO172 code. I am guessing the fuel pump, maybe even the cap??


Check the fuel level sending unit first. My wife's Xterra has the same issue and from what I heard tey use the same unit.

[far2grumpy]

Ok update here.. Replaced spark plugs and code went away.. yay.

Now there is another problem, when it gets down to a 1/4 tank of fuel it throws a PO172 code. I am guessing the fuel pump, maybe even the cap??

brian1973 ... not sure if you have info regarding P0172 causes, here's extract:

DTC P0172
Circuit Description
The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open Loop and Closed Loop. During Open Loop, the ECM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop, the oxygen sensor inputs are added and used by the ECM to calculate the short and long term fuel trim. If the oxygen sensors indicate a lean condition, the fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, the fuel trim values will be below 0 percent. The short term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. The long term fuel trim makes coarse adjustments in order to maintain Air/Fuel Ratio of 14.7:1. The fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the evaporative emission (EVAP) canister is causing a rich condition. This DTC is continuously monitored during engine operation. If the ECM detects an excessively rich condition, DTC P0172 sets.