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Old 05-13-2019, 01:46 AM   #13
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Join Date: Dec 2018
Location: Nevada
Posts: 107

2007 VUE 3.5L
Default Re: p0420 AND p0430 - 2007 Saturn Vue 3.5L V6 AWD

Originally Posted by fdryer View Post
O2 sensor spacers may not be effective if both upstream sensors fail to output signals. Its presumed a weak sensor may benefit from the extension tubes but not if sensors are dead.

Presuming '05 Vues are the same as '07s, both using 3.5L engines, service manual descriptions for P0420/P0430 may help.

DTC P0420 or P0430

In order to control emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), a three-way catalytic converter (TWC) is used. The catalyst within the converter promotes a chemical reaction that oxidizes the HC and the CO that is present in the exhaust gases. The oxidation process converts the HC and CO into harmless water vapor and carbon dioxide. The catalyst also reduces NOx by converting NOx to nitrogen. The powertrain control module (PCM) has the ability to monitor this process using the fuel control heated oxygen sensors (HO2S) and catalyst monitoring HO2S. The fuel control HO2S produces an output signal which indicates the amount of oxygen present in the exhaust gases entering the TWC converter. The catalyst monitor HO2S produces an output signal that indicates the oxygen storage capacity of the catalyst in the TWC converter. The oxygen storage capacity of the catalyst is an indicator of the converter ability to convert exhaust gases efficiently. The fuel control HO2S output signal will be far more active than the catalyst monitor HO2S output signal when the converter catalyst is operating efficiently. if the PCM detects a level of catalyst monitor HO2S activity that indicates the catalyst is no longer operating effectively, this DTC will set.

*DTC P0420 Catalyst System Low Efficiency Bank 1
*DTC P0430 Catalyst System Low Efficiency Bank 2

What's puzzling is the lack of error codes pointing to each upstream sensor failure like;

DTC P0133 or P0153

DTC P0135 or P0155

DTC P0137 or P0157

DTC P0138 or P0158

DTC P0139 or P0159

DTC P0141 or P0161

If you can, try Autozone or other auto store providing free OBD II scans for error codes to see if other codes exist.
I took it to Autozone when I rented the O2 sensor socket, they pulled the same two codes as in the OP They told me both catcons were dead and it would be $900 for parts. I tried a CarMD scanner just now, same two codes.

I will probe around the harness again tomorrow, thank you for the diagram!! Amazing!

I tried to get the upstream sensors off to test them on the cooker but I ran out of daylight and they are really stuck on there. I left them in penetrating fluid for tomorrow. Will update then.

Is there any reason the codes would give 0 voltage via the scan tool? It could be a bad harness, it could be two dead sensors, could be a bad scan tool, scan software issue, but if the harness is ok and the sensors are fine, are upstream sensors on a seperate fuse or is there anything else to check? When things go out in pairs, I get a little skeptical about other things at play!
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