Oxygen Sensor replacement Pre and Post Catalytic DIY P0420

[Derf]

Video linked below shows replacement of pre and post catalytic converter O2 oxygen sensor.
Link: http://www.youtube.com/watch?v=Y0wjJ6YFPSc" onclick="window.open(this.href);return false;

Had been getting a random P0420 error for the last 2000 miles. It seemed to come on when starting on cold days, but would occasionally come on at other times. Details from the previous owner, they had the post catalytic sensor replaced about 25k miles ago. After the sensor harness was damaged by driving over roadkill. Knowing that the rear sensor was newer and the condition seemed to be related to cold, decided to first replace the pre cat sensor. After about 300 miles this made the code come on nearly every start up. Given the history of the vehicle, the best guessed turned out to be wrong. Replaced the post catalytic sensor, the previous replacement was not OEM, things are now good.

Used the following parts for 2005 1.8L FWD. AWD, 2.4L, and other years might use different versions. Shopped around, NAPA, Autozone, Advanced, Oriely's were all within a few dollars of each other. Of all places, Amazon had the best deal by a long shot, (May 2014) on the sensors and socket.
Pre Catalytic Convertor Denso P/N 234-9052 ($88.26)
Post Catalytic Convertor Denso P/N 234-4233 ($47.30)
Socket set used: Alltrade 948005 Master Sensor Socket Kit - 7 Piece ($24.58) Okay quality, for shade tree mechanic. For both O2 sensors you will use the 7/8" crows foot socket.

Things learned from the P0420 error code:
-Code is vague, only gets you in the vicinity of the problem Check out the following video for tips on diagnosing the problem: https://www.youtube.com/watch?v=9VZ5K8n5jj0" onclick="window.open(this.href);return false;
-Guessing which 02 sensor is causing the problem is a best guess. Unless you have the proper scan tool.
-Post cat sensor can easily be damaged due to open air wiring that roadkill, debris, and weather can impact.
-Do any engine flushing cleaning before replacing the O2 sensors, prevent damaging the new sensors

[kostby]

WOW! What a great, detailed step-by-step video and explanation, Fred!

The procedures don't look that daunting, but I don't have ramps, so I still might have someone else do it. Now I understand what they should (and should not) be doing and charging me for!

Thanks!

[Derf]

WOW! What a great, detailed step-by-step video and explanation, Fred!
The procedures don't look that daunting, but I don't have ramps, so I still might have someone else do it. Now I understand what they should (and should not) be doing and charging me for!

Thanks! I tried to use ramps, have not found any the Vibe can roll onto, most are too steep and the front cowling hits the ramp. Found jack stands or stack of lumber work best. Most shops will overcharge for this repair because they know you can not pass the emissions check without it.

Several times while getting exhaust work completed, I had a shop "fry" the O2 sensors in the exhaust through improper grounding when welding on the exhaust pipe. If you do not disconnect the battery before welding on a vehicle, you are just asking for problems with the on board electronics.

[Raven]

For the ramps, I use pieces of 2x6 to lessen the angle. The car is only on the wood to start up the ramp and then rolls on to the metal to the top resting spots. My Vibe is lowered 2 inches and my 3 Subaru SVX are low to begin with. It works very well.

[vibenvy]

I got a set of Rhino Ramps on eBay right after we got our Vibes in 2009. The Vibes roll right onto them without any rubbing on the underside of the front bumper covers. With the 16" winter wheels and tires, the front bumper covers just barely clear the ramps, but still don't rub. Best ramps I've ever used for sure!

[Chiadog]

Great info! Thanks.

[lannvouivre]

Note: For 2005-2008 year model 1ZZs, the pre-cat sensor is an air/fuel sensor that costs waaay more.

[Derf]

Note: For 2005-2008 year model 1ZZs, the pre-cat sensor is an air/fuel sensor that costs waaay more.

Thanks, reworded main posting. Most parts places wanted around $175 for the pre cat sensor, finding it new for just over $80 was a bargin

[lannvouivre]

Thanks, reworded main posting. Most parts places wanted around $175 for the pre cat sensor, finding it new for just over $80 was a bargin

It's a real kick in the teeth when you find out the 03-04 O2 sensor is only $30-40.

[circuitsmith]

It's a real kick in the teeth when you find out the 03-04 O2 sensor is only $30-40.

That's the price of DBW + lower emissions.

[Derf]

600+ miles and no more codes. The post cat sensor was the problem this time... Point, use OEM parts when replacing electronics/sensors, the non-OEM unit from the previous repair failed prematurely.
Saw many posts about failed catalytic convertors, pitty that something so essential can have repeat issues. Appears most catalytic system fail once they go below 95% efficiency.

[cythraul]

Thanks for the great write-up! It convinced me to take care of my sensors myself..

I have these on Torque (Android app with bluetooth OBD2)

Current fault - P0138 - Powertrain - O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
Pending Fault - P2195 - Powertrain - O2 Sensor Signal Stuck Lean bank 1 Sensor 1

I'm confused as to why both sensors are failing at the same time. I'm assuming sensor 1 (pre-catalytic) is wrong and throw off the sensor 2 reading... I'm no mechanic realy. :)

I'm having a hard time finding a deal on the needed sensors here in Canada. Cheapest I could find is on canadapartsonline.com: 60$ for 234-4233 and 110$ for 234-9052. Plus 25$ shipping!

Beyond the price, I was wondering if anyone knew why these online part shop are suggesting 234-4209 as well as the 234-4233 for my 2007 Vibe FWD? Can't find any difference.. except a few dollars.

thanks!
cyth

[Derf]

I have these on Torque (Android app with bluetooth OBD2)
Current fault - P0138 - Powertrain - O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
Pending Fault - P2195 - Powertrain - O2 Sensor Signal Stuck Lean bank 1 Sensor 1
--02 Sensor issues require a lot digging to figure out the cause. On mine I replaced a good sensor, not taking to time to really look at the problem. I did not get the same faults you did, not sure the about your issue. Check the video I linked to in the original post. The mechanics tips may help you hone in on the problem.
https://www.youtube.com/watch?v=9VZ5K8n5jj0" onclick="window.open(this.href);return false;

I'm confused as to why both sensors are failing at the same time. I'm assuming sensor 1 (per-catalytic) is wrong and throw off the sensor 2 reading... I'm no mechanic realy.
--Yes, one faulty sensor can cause the ECM to get confused thinking the opposite sensor or both sensors are bad. So you have to work through the exhaust system to find detectable issues, temperature change in catalytic system, broken wire lead, corrosion in connector,etc

I'm having a hard time finding a deal on the needed sensors here in Canada. Cheapest I could find is on canadapartsonline.com: 60$ for 234-4233 and 110$ for 234-9052. Plus 25$ shipping!
--That is high, glad Vibe parts are plentiful in the lower 48. I was surprised that Amazon was big on car parts and usually cheap, not sure if that is an option for you.

Beyond the price, I was wondering if anyone knew why these online part shop are suggesting 234-4209 as well as the 234-4233 for my 2007 Vibe FWD? Can't find any difference.. except a few dollars.
--O2 sensors are somewhat generic, once part may be for a Corrola, the other for a Matrix, another for the Vibe. The sensor in all three perform the same function but could have different connectors at the end, different baffle on the sensor tip, or length of wiring pigtail.

[cythraul]

Just received the new sensors from RockAuto.. fair price (for Canada) and relatively cheap shipping if you choose consolidated shipping to Canada but it's awfully slow! One must not be in a hurry. I ordered the 29th of November and it got here only today: December the 9th.

It's snowing here and I'm a wuss so I won't tackle the second unit just now but I wanted to replace at least the first one today.

Unfortunately, I don't have the right oxygen sensor socket.. I have both the long and short 3/8" (left and center below) but I need the other 1/2 one.. (right on the picture.)



You see, the long one is too long to fit between the sensor and the firewall. I could almost made it but because of the brake hub (hope I get that name right, :) it would not go. The middle one does not reach far enough under the plate protecting the exhaust pipe.

Obviously, nobody would want to remove the plate. Whatever is holding it is so badly rusted that I'm sure it will disintegrate if I look at it too closely.

For the record, the two o2 sockets I have are the Lisle 12390 and OEM 44001 (Canadian Tire exclusive number, it's actually 25001.)

Canadian Tire can't help me and I don't know any local shop that carries such tools. So back to ordering stuff and wait and wait and wait. :(

[bull77]

whew -- been awhile since I've been on the forum

'06 Vibe with 330,000kms and going strong -- but I'm getting these two errors: P171 and P420.

Question: Since it's the dead of winter I'm going to replace the precat o2 sensor first. What are the chances both sensor are bad? Is there a way to tell outside of replacing one and seeing if the code disappears?

I'm also replacing the MAF sensor.

[Bookworm]

In general, if one is going bad, the other one has been affected. It's always suggested to replace them in pairs.

[zbyers]

Generally P0171 is an intake manifold gasket leak
P0420 is the kitty on it's way out.

Have you diagnosed the sensors themselves to determine they are the culprit?

Odds are your MAF is fine so replacing it is probably a waste of time and money.