P1436 Revisited

Commonly, this manual manipulation is only temporary fix...
Anyways, if you drive by auto parts place borrow their OBD-II and reset the codes for free. Or it will clear after so many starts. It may also be from detecting O2 readings, and you can read those with same OBD-ii reader to double check that it is more than the diverter valve.

 

I got my ZEP from ebay. Kind of expensive, but it works!

Joe

 

I've never found the bypass valve to be "sticky" inside or outside, but rather has free full movement but it feels stiff as if the factory spring is too heavy (though it is not). Does corrosion cause this? Could there possibly be enough vacuum pressure to open this thing? I've installed a light spring to aid the valve 'open' position as an experiment. Next, I may remove the 'closed/restricted' spring load as suggested. BTW, has anybody dissected one of these bypass valves to determine what is going on inside?

 

How does the 2002 Prius determine that the bypass valve is not opening or closing, there are no sensors in the three cat system for this? I will tell you how it knows, it is all in the VSV solenoid valve.

bypass valve is normally open, upon start up engine VSV Solenoid is energized allowing vacuum from intake to flow to through VSV to HCAC sensor and to bypass valve, therefore bypass valve is closed, and sensor knows there is vacuum, when the cat system is warmed enough the VSV valve is de-energized therefore vacuum is cut to bypass valve and it is opened again. Problem is that if the air intake in the VSV valve is clogged, the HCAC sensor still senses vacuum. Furthermore if air is not allowed into the system there will still remain vacuum at bypass valve and it will not open. Look at the VSV valve, it has a air intake. When it is de-energized the air intake lets air in. This must be clogged so vacuum is still at the sensor which is what sets off the DIC p1436. If you take the vacuum hose off the bypass valve you will allow air into the system when it is de-energized and have no check engine light anymore.

 

"VSV valve is clogged"
Is that the round canister with the linkage arm?

"If you take the vacuum hose off the bypass valve..."
And do what? Plug it?
"have no check engine light anymore"
How long have you experienced this? Once we do this, and nothing else a factor, can we be confident it will pass state emissions test ?

 

Personally I removed the vacuum line coming from the tee of the VSV valve by the dipstick tube. This is the part I am thinking is the problem. Then I took a foot long piece of vac hose with end plugged and attached it to the plastic tee coming from the VSV. My error code was p1436, that's vacuum valve open. I think it's the VSV not letting the bypass valve open all the way once the engine worms up because there is still vacuum to it. The bypass valve will need to be manually opened all the way if it is stuck for the car to operate properly once you unplug the vacuum and cap it off. I haven't tested the car long enough to know if it will work. It is just theory for now. Regarding passing emissions, no car will pass with check engine light on. The best way to know if it will pass is to do what I said, clear code and drive a few trips. If check engine light is off and a code reader shows all systems have run their test sequence and are ready you are safe to pass any emission test. My code reader has a green light that means all systems are ready, amber meaning not ready and red meaning codes exist.

 

Joedirte posted a picture of the vsv valve the sensor and hoses on the first page 3/4 of the way down. It is located by the engine dipstick tube. The vsv valve has wires running to it and a plastic tee that has a hose that runs to a steel line, which runs to the bypass valve on the HC Absorber behind the catalytic converter. I haven't removed the vsv valve and inspected it, but I bet it has a inlet pipe with a filter that allows air to enter to purge vacuum from bypass valve when valve is supposed to be opened. This is what I think is clogged or not working.

 

Lets back up to what I think we know:

Road salts cause the bypass valve to malfunction.
We haven't had anybody confess P1436 from non-road salt locations. Or have we?
Something inside the valve, once corroded, prevents it's intended operation.
"DTC P1436 will set if the bypass valve does not perform normally under the following conditions. During a cold start (bypass valve closed) and after the coolant temp has reached 113 degrees and the engine load factor exceeds 30% (bypass valve open)."
Apparently one would have to spoof the sensor somehow to alleviate P1436 or replace the bypass valve (front pipe assembly) as stated in the Toyota Manual.
I'm not smart enough to do the former and not willing enough to do the latter. However, I can purchase a clean salvage front pipe assembly for less than half of new price. Too risky?

Question: Do O2 sensors and the HCAC have a life span or are they considered good until they set a DTC?

BTW...
I've removed the VSV vacuum switch valve (on the right in Joe's assembly picture) and found the little black plastic canister on the bottom does have a filter inside. I slipped the canister off and blew in/out and air passed through freely. I've never tested vacuum on a vehicle, but it seems to me it would take a lot to operate my bypass valve which it very stiff when operating by hand.

The check valve (with the orange end) that connects to manifold vacuum also allows air freely toward the manifold and correctly restricts air opposite direction.

 

Ok, so salt rusts the butterfly mechanism so bypass valve sticks and sets p1436. So if you remove the mechanical arm on the bypass valve, so it thinks it is moving the butterfly valve inside the HC Converter but it is not and still get a check engine light code p1436 that means rusted valve is not the only issue or not the issue at all. What does it know if the arm moves or not, how can it tell? It uses the vac sensor by the VSV. P1436 is set when computer says sensor should not have vac but it says it does or computer says sensor should have vac and it reports I don't. That means that vsv didn't allow vac to enter through that screen and if you unplug the vac line and plug it, then vsv sensor should not sense vac when it is released and no check engine light. Hopefully

 

O2 sensors don't last forever naturally. But the O2 sensor has nothing to do with this topic.

 

Do what I said in my first post unhook the vac line, plug it, clear the code and see if it comes back. Then report back.

 

Reason why I ask about O2 sensors is now I have set codes P0171 (bank1, senor1), P0130, P0133.

 

I would first clean your mass air flow sensor ,than erase the codes and see if they come back. If they come back sounds like your air/fuel sensor is bad..

 

Update. I swapped out the front exhaust pipe with a very clean (no road salt corrosion) salvage part I got from an individual in AZ where I now reside. P1436 is gone.
I did get codes P0171 (bank1, senor1), P0130, P0133 afterward, and twice cleaning didn't help.
A local mechanic's diagnostic software indicated that the solution was most often to replace the MAF Sensor. I installed a new Denso sensor and all DTC's are gone. Next up, emissions test.
Also, A/C isn't cold after non-use during winter.

 

Since I replaced my front exhaust, now I have this old one and I'm thinking about cutting it open at the Bypass Valve just to hopefully see what's going on inside. Anybody, have any input or advice before I begin the autopsy? Anybody care? Or would you rather forget about Toyota's historical little gem of a part that is susceptible to road salts that they built into a tiny $1000. (on ebay) exhaust system? Is my sarcasm justified? Yay, I know...what should I expect still driving a 13 yr old concept car?

 

If you can take pictures during the autopsy and post them it would be much appreciated! Actually seeing the inner workings may help others figure out better how to keep it working. Good luck!

 

I'll see what I can do. It will be a few days before I get to it though.

 

Is there a confirmed way to get this valve to stay in the open position? I live in a state with no emissions test. Would it effect performance to leave it open all the time?

 

When greasing or lubing this, do you just hit the outside linkage or is there a way to get inside?