P1436 Revisited

You should contact Eric at Adopt a Part in Denver. He has username freidawg here at PC. A salvage front pipe would be the way to go, but laws governing emission systems are tricky.

 

Hi Phoenix,
Reading your post.... any resolution to the problem yet? I live in the Rockford, IL area not far from you. So I have the same snowy weather and resulting wear & tear issues as you. Have the same issue just starting with my 02. Owned it since 04 and have put 125K on it with no problems... this is the first issue. Reading other posts, I have decided to try lubing the mechanical valve first. How bout you?

 

Friedawg/Eric has posted here that he would not sell used catalytic converters. Strictly speaking it is illegal per EPA. However, the bypass valve itself may be a separate or separable component? If it does not specifically perform the catalytic function, it would probably fall outside the EPA rule area.

 

I have periodically gotten a P1436. Generally I found the vacuum operated valve had become sticky due to road grime/salt/junk. I have successfully lubed it about 6 times over the past 6 years. The first time I got this code, the car was fairly new, and the dealer (under warranty) replaced the entire assembly. Then about 1 time per year, usually just after or during winter (NYS), the code came back. I then started the lube idea. I just got the code a week or so again, after about 1.5 years without it (and about 30,000 miles). I lubed it last weekend, but it came back 2 days later. I will try it again - but this time disconnect the vacuum push rod, so I can loosen up the valve better. I hope it will work again.

steved
02 super white 229,000 miles.

 

This is my first post so here goes nothing.
I have heard a lot of people who say to "lube the valve". This is not as easy at it sounds. My 2002 Prius just failed emissions in Massachusetts and I was quoted $2,200 to replace the exhaust. I looked under my car to "lube the valve" and found a stainless steel shield completely encasing said valve. I had to pry the thing apart and destroy it with a hammer and pry bars. After that, I tried using the suggestions on this website of "high temperature grease". That doesn't work as the CAT gets over 500 degrees F.. My solution that worked best was to clean off all the burned on high temp grease and give it a generous spray down with a product called ZEP 45. This stuff worked exactly like we need for this type of repair. After 3-4 sprays and some light prodding with a pry bar, I was able to get the valve moving. The next "trick" was to use a vacuum pump from harbor freight to get it moving using vacuum instead of prying or wiggling it. After a couple more sprays of Zep 45, the vacuum pump was pushing and pulling it like it was new. The next step was to spray on some ZEP GROOVY first in the open position and then in the closed position. That allowed even penetration into the nooks and crannies. The ZEP GROOVY is an anti seize lubricant that is not supposed to break down until around 2000 degrees F which should do the job nicely. I ran my car on 4 short trips and the check engine light went out. I have checked and rechecked the movement of the valve and it is smooth as silk. I don't see any way to salvage the heat shield, but that was a bad design anyway as you can't get to the screws to remove them once the exhaust is installed on the car. OK- I'm done!

 

That's a great story! I like ZEP products too.

 

Well the valve seized up again. I can lube it up with the ZEP and it works for a while, but it seizes up after a couple days. Can anyone else suggest a "high temperature grease" by brand and part number that works? Nothing seems to hold up to the temperatures generated by the catalytic convertor. It seems to me there should be some product that can work at those temperatures.
I still need an inspection sticker in Massachusetts!

 

Have you found a solution to the sticky valve?

 

It is my belief the valve is sticking internally. So far the only long term solution is $1200 or whatever nonsense for whole new thing. I will say the high temp graphite stuff doesn't work long term.


If you rent a brake hand vacuum pump you can throw a tube on the diaphragm and try to manually work the valve. Doing this allows you to feel how far the linkage is moving. And probably apply more vacuum than from the throttle body. I'm guessing you do NOT want to damage the diaphragm.

You probably know this but the linkage moves a plate inside the HCAC. The part that is sticky could be the spring loaded part that the linkage moves, but I think it is the diverter plate inside the exhaust that is rusting to the side.


A view from below:



And a side view.



I have a theory about using a small vial of liquid phosphoric acid (the anti-rust stuff you can get at Lowes aka Naval Jelly ) and drop it down where the arm enters the linkage. That will convert the rust to FePO4 which hopefully might unstick it. I do not know what it might do in the catalytic converter and if you would follow the phosphoric acid with something like water or baking soda in water after you worked the HCAC around. So don't try it at home. Maybe someone has a junkyard HCAC that can be experimented on..



I'm sure no one would want to circumvent the lame attempt by Japanese engineers to get around some US emissions standard, but without the spring you might be able to wedge the diverter open so that the exhaust would continue through the cat like a normal car and not use the small passageways on the side. Not sure why the default failure mode is stuck on restrictive flow. The arm should have to move to restrict flow, then it would fail gracefully.

 

I am also in salty Rockford, IL.
Our 2001 with 135000 miles has suffered from the squeeky HCAC valve.
I lube it occasionally with high temp anti seize and its been fine for a couple of years.
Knock on wood, it will last a bit longer.
-Dave

 

I wonder how it detects the frozen valve?

I can see forcing the valve open as a reasonable workaround. What I don't understand is what sensor or how the car detects detects the position of the valve?

Bob Wilson

 

Oxygen sensor general info | PriusChat

HCAC errors
P1436 - Bypass Valve Malfunction
* Bypass valve not operating during cold start or warm coolant but engine load > 30%

P0420 - Catalyst System Efficiency
* deteriorated response for Sensor 1 Bank 2 (downstream)

So it appears the vacuum to the valve has a electric valve and there is a Tee with a Vacuum Sensor on it (right next to the oil dipstick handle). I believe this is the line that goes to the HCAC valve. Since the Bypass is active on cold, startup, and "Scavenges exhaust during cold start and during deceleration".

So my assumption is the vacuum is either a PWM or proportional valve, and the sensor can tell when the valve isn't all the way open(?).

Otherwise maybe it senses more back pressure causes by the reduced flow through these channels:

I guess I don't know enough if you could sense that in the MAF, if the exhaust was restricted.

One experiment would be to clamp the hose to the diaphragm and see if you throw the same code, ie. more vacuum, but valve is stuck shut... (LOL, I just now realized a vacuum gauge on that hose would be more revealing..)


(My assumption and someone could carry out this experiment, if you unhook the linkage, the diaphragm could move in and out freely, and maybe trick the vacuum sensor into thinking it is operating normally. However the bypass valve defaults with spring load to closed (aka restricted)

 

I am wondering if the diaphragm might have a small, 'leak hole.' If the linkage is frozen, the diaphragm won't uncover the 'leak hole.' This causes the line vacuum to remain high instead of decreasing as the 'leak hole' is uncovered. More important, the change in vacuum pressure would be needed to spoof the car into thinking it is working.

I like the idea of using a vacuum gauge to monitor what happens.

Bob Wilson

 

Bob, I know the far side of the diaphragm has a hole (to let air in as the pink rubber bladder moves towards the back. I'm pretty sure there isn't any leak hole when I had a hand brake pump attached to it. It didn't leak.

My only thinking is that the diaphragm is displacing about half a soda can worth of air as it retracts. I'm assuming when valve opens to manifold vacuum, this won't take very long. Not sure how the vacuum sensor would detect valve position, but it does look like pretty fancy three wire vacuum sensor. The sensor appears to be standard Toyota MAP sensor.


Not that you cannot find it in the front of the engine, next to oil dipstick, but here is the assembly.
On the left is the vacuum pressure sensor, the middle is a check valve that connects to manifold
vacuum, and the right is the VSV vacuum switch valve.



The DTC is more accurately:
P1436 Toyota-HCAC-System By-Pass Value Improvement-Open Malfunction (Pri)
P1437 Toyota-HCAC-System By-Pass Valve Close Malfunction

V 1 Vacuum Sensor (HC Adsorber and Catalyst System) sendor is (HCLS) is pin 14 on E9 connector to Engine ECM (and shares +VC and gnd with the gas pedal and vapor pressure sensor)
V3 VSV (HC Adsorber and Catalyst System) vacuum switch (HCC) is pin 20 on E9 connector to Engine ECM

Is there anyway with scan tools to read the sensor input for HCLS? I might go back probe the voltage on the harness..

 

Hi. I am in MA. I took the front pipe out because it is held in by two bolts front and two bolts back. A propane torch loosened the nuts. That way I was able to remove the cover and then wiggle the valve. Got it working and went without the 1436 code for a while but now it is back, even though I can see the valve working (I did not put the cover back on, though did chase the threads and have SS nuts to keep from rusting too much. Thanks for the tip on ZEP products. With the cover off, I can still access the valve, so should be able to just spray it. I did use Lithium grease before but perhaps is is not good at the temperatures concerned. Who has ZEP products? Autozone? Advance Auto? NAPA? Thanks

 

Well I found you can can diagnose the valve moving while driving on the freeway by using any OBD-II scanner. If you check the downstream (O2V12) it should move slowly around 0.5V to 0.8V. Now when you coast on the freeway, maybe in B mode also, it should active the HCAC bypass. I'm assuming also at stop lights...

I noticed the O2 steadily dropping once on the freeway when kind of coasting for over 30 seconds and when accelerating again it went back to normal. But maybe I'm wrong and it is from the STFT adjustments...

 

I love Priuschat! I have a 2001 bought new 12 years ago. Just got the 1436 code and was quoted for a new catalytic converter. PC directed me to the right info. A little Seafoam spray and a lot of wiggling that valve arm around and it loosened up. I put high temp grease on. It seems to move well. Will the idiot light go off or does it have to be reset? Thanks!