CEL codes morphing, confused.

[SiennaDriver]

2000 Sienna, 110k miles, reasonably well cared for and hoping for many more years from it. It has the California emissions design.

CEL displayed only a P0420 code, I lived with the CEL on for awhile and when I went to address it that code was gone. But P1150 and P1155 were active.

Am I looking at a defective sensor, converter or maybe both?

And I see online that the current code could be bank 1 sensor 2 (after the cat) or, from a recent post here "P1155 CODE IS BANK 2 SENSOR 1".

Where should I begin a driveway diagnosis?

[wiswind]

P1155 is a heater current less than 0.25 amps in the oxygen sensor in bank 1, sensor 1.
This is the front bank of cylinders and this sensor is located in the front exhaust manifold.......very easy to see.
P1150 is also for the same sensor, the ECM (computer) is not liking the input from the sensor.
I would check the connector for that front oxygen sensor, but if you do not find anything wrong at the connector, you would be looking at replacing the front A/F sensor.
I would use the OEM version, which is DENSO......you can locate the correct number at the Denso direct fit aftermarket site or from an online toyota dealership.
I have used toyotapartszone.
Once you have the DENSO numbers, you may be able to shop around......list price for this sensor is over $200, you may be able to locate it cheaper, even from a TOYOTA dealership.
Personaly, I'm a stickler for having the exact, correct sensor at this location......it needs to be matched in switching charactoristics to the A/F sensor in the rear (bank 1) bank of cylinders.
The A/F sensor is a "wide band" oxygen sensor and is used by the ECM to make critical adjustments to the motor operating parameters, particularly how much fuel to spray into the cylinders for each firing.

I had a P0155 code from my front oxygen sensor, but it still was working just fine (although I would not have passed an emissions test in most any state with the CEL on).
I still went from open loop (warm up mode) to closed loop within 15-20 seconds of starting the vehicle in the cold winter weather.
So, I am thinking that with the additional code that the actual signal from the oxygen sensor is not acceptable, you have either a connection issue or, more likley, a defective sensor.

[SiennaDriver]

Denso 234-9007 is for the 2000 California front left

Denso 234-9009 is for the 2000 California front right

I assume that replacing the one by the radiator (left, I believe) is the right way to go.

The connecting plug looks fine - removed and sprayed it with electronics cleaner and that didn't change a thing. Cable looks intact.

Thanks for steering me in the right direction.

[SiennaDriver]

Finally able to also check this with a meter. I connected a VOM to the black terminals of the sensor and the meter did nothing. No continuity, no resistance readings, didn't respond to any settings. I assume that means the heater in the sensor is useless and that I need to replace the part.

Could someone verify that and confirm that the sensor by the radiator is the left, as described in my prior post.

Thanks.

[wiswind]

The "left" side of the motor......in a front wheel drive vehicle is the side that would be on the left if the motor were turned 90 degrees so that the transmission is in the rear (instead of driver's side) and the alternator is in the front.
This would, as you mention, have the side of the motor that is closest to the radiator be on the left side of the vehicle (driver's side).

From the reading that I have done, the 2 "Air / Fuel " sensors are actually identical, just a slight difference in lead length.

[SiennaDriver]

Fixed, was actually pretty simple when all's said and done. Runs great.

Thanks for the help!

[SiennaDriver]

Um, cancel that runs great I posted a few days ago.....

So I replaced the original sensor located behind the radiator with a Denso 234-9007 and cleared the P1150/1155 codes with a handheld device.

Have driven about 100 city miles. During that time there was a P1130 pending which vanished, and now there's a P0420 pending. There was an active P0420 some months ago and cleared itself about the same time as the sensor I just replaced failed.

What happening, what am I in for next?

[SiennaDriver]

P0420 active now. Looks like it could be the sensor or the converter.

Any home style checks for monitoring the sensor behind the cat?

[wiswind]

The P0420 code could be a defective sensor, or it could be reporting a weak catalytic converter, or the ECM (computer) could have logic that needs to be updated (replacement of the computer).
Those are the solutions that seem to be the causes as far as TOYOTA seems to be indicating.
I don't know of a "easy" way to test to determine which it is.
I listed them in order of cost and ease of repair, although the sensor replacement is dependant upon how rusted the bolts that hold it in place are.
They are nuts that screw onto studs on your exhaust pipe to the rear of the catalytic converter.


The wires from the post catalytic converter sensor (downstream sensor) pass up through the floor of the vehicle and plug into a connector under the passenger seat.
Removal of the passenger seat is NOT required.......remove the plastic trim panel that is at the base of the passenger seat mount......on the driver's side, bottom of the passenger seat.
Below the left hand cup holder on the side of the passenger seat.....you will see the sensor wires come up through the floor of the vehicle and you can easily reach the plug.
The plug will have the standard "tab" that you push to release the plug from the connector.

[Black Sunshine]

Great pics Wiswind! Why is your van so clean underneath? It's kinda freaking me out. There's no part of my van that is that clean.

[SiennaDriver]

Excellent pictures and description!

A strange thing happens, the P0420 comes and goes. Sometimes the dash light is on, sometimes it's off and the code is shown on a handheld device as pending, other times there's no code at all.

Tempted to buy an after cat sensor and see if it helps. It costs less to do that than to have the part diagnosed at Toyota; that is as long as I can loosen this:



What would cause a sporadic code? There are no leaks in the exhaust system that I can detect.

Also, some time ago this was done at a professional muffler shop at the same time the flex pipe was replaced. Could this "excess" have also been in the pipe and, if so, affected the converter either with the broken off glass like shards or outgassing material?