I have the infamous P0420 code.

This is not too difficult to diagnose. Your catalytic converter is becoming marginal and the cold weather slightly impairs its efficiency, causing the sensors to show diminished converter activity.

Either you can replace the catalytic converter or you can try replacing the upstream oxygen sensor in hopes the new sensor will show greater voltage swings than the original, which will persuade the engine ECU that the cc is OK. It is much less costly to replace the upstream O2 sensor vs. the catalytic converter, so I suggest doing that first.

 

I agree with Patrick. I recently had one with the same code, swapped both sensors to no avail. Pulled the cat. conv. assembly off and found a weld that was cracked through. I'm not sure if the resonator was stopped up causing the crack/burn through. I replaced the whole assembly and the code was gone.
I also have an 01 that had a bad exhaust leak. So I dropped the cc assembly on that one and found the weld cracked around 90% of the circumference, only at the other end of the cylinder. I pulled another one off my other parts car and changed it. Now it's quiet again. I welded the bad one up and put it on my parts car in case I need it later. I just thought it was strange that the same part had welds that failed to hold together. They were cracked through the center of the weld.

 

If all you need to do is pass emissions, you can put the spark plug non-foulers on the O2 sensor near the cat. This should get you by the test and might just make you feel good enough to forget about the code. It does not fix the issue, just the code. Could also would just need to replace the upstream O2 sensor (the more difficult one to get to but not that hard). I did both of those on my old 2002 and never heard back from the code. Depends on how much money you want to dump into the problem.
TomK

 

Anybody named Winterkorn in the family line?

-Chap

 

car has had code for years according to previous owner, have a pair of Denso 02 sensors only for emissions testing and timing the drive cycle to end just as I roll into the emissions testing center.

 

Yes, at that odometer reading, considering you are socially conscious, and plan to keep the car for a while, I suggest you replace the catalytic converter as well as the upstream O2 sensor at minimum.

 

Assuming the engine uses no oil (i.e., sends it out the exhaust,) I agree with Patrick.

Bob Wilson

 

Winterkorn? I do not get it. Obviously it is a rip on me.
TomK

 

Bob Wilson, what products would you suggest for servicing the catalytic converter exhaust diverter valve on a 2003 Prius. Some post suggest keeping this valve trouble free and lubricated to help ensure correct converter operation. I'm a huge fan of preventive maintenance and since I gotten my '03 project vehicle operating well I intend to keep it that way. Vehicle has 222421 at present (purchased @ 221305) with a few issues. Changed Inverter pump, cleaned throttle plate and MAF, resent TPS and Throttle Motor connectors, replaced license plate bulbs replaced all fluids and all filters to this point. Total cost of all repairs $319.62. Got it from 33.1 to now 45.3 MPG so am satisfied to this point. Just hoping you might advise on preventive maintenance on Diverter Valve. Had two P0420 in cold weather but nothing has surfaced in almost 5 weeks now. Vehicle uses no oil and since I cleaned the Throttle Plate and MAF and reset connectors, NO Issues. Mileage then to 45.3 in all city traffic, mostly short hops. Not optimum but satisfactory to this point. Thanks for all your input and advice. I do all my own maintenance and repairs and have Techstream, lab scope, DVOM etc. Would have never attempted this if I had to rely on dealer repairs. Cost prohibitive.
Thanks Again. Peace to all.

 

I'm not Bob, but back when I bought my Gen 1, I slithered under it with a jar of ordinary silver-colored antiseize and used a thin dauber to get it around the diverter valve shaft wherever I could, and worked the valve back and forth by hand several times. I think I re-checked it one other time in the eight years I had the car, and I may even have put a bit more antiseize on at that time. Never had a lick of trouble with the diverter.

-Chap

 

Thanks Chap. I have a bottle on my tool box for spark plugs. Will take care of the job tomorrow. I'm also need to figure out the frontal air dam to block cold air to aid ICE operating temps. Will start with foam to get ideas, than make something for long term. You guys have been a great help during my apprenticeship on the Prius. Thanks millions.

 

Chap, Serviced the diverter valve this past weekend. Bit of a chore as it is incased in shields. Will keep an eye on the area. Valve appears to function as it should so hopefully all will remain so. Anti-seize I have is good to 1600*F, so temp not an issue. Thanks for the heads up on this issue. These vehicles are very interesting in their operation. Learning the technique in operating it and the best speeds, will see what raising ECT, clean and wax and cleaning up "ground effects" changes. Shooting for 50 MPG.

 

For those interested, I lowered the ICE oil level approximately 1/3 down from full with engine dead cold. Cleaned manifold, and installed radiator blockers in lower inlet and to two smaller upper inlets. I left one opening in the lower inlets open. With these areas covered, the ICE operating temperature ranges between 180-185*F. Checked the temperatures with Mini VC. This also allowed the engine to reach 118*F in approximately 4.6 - 5.1 minutes from cold soaked (30*F). Blue temperature indicator extinguishes then. We warm the engine to 118*F before driving on almost all occasions. So far this had eliminated all previous issues (P3190, P1128, P0420). Vehicle is primarily used for in-town runs with occasional highway (short runs). I purchased a battery maintainer for the 12V battery and monitor the voltage. This may also have helped as I keep the 12V @ least 75% charged. As for the P0420 (had it twice since purchased in September) I will inspect exhaust system as weather warms. I think there may be a small leak or flex at the flex coupling. As we don't have 240 inspections here I can work through this as time allows. Vehicle seem to be running fine as my wife drives it every day several times.