View Full Version : 4Runner emissions failure

01-14-2011, 08:12 AM
A coworker of mine has been having a rough time with his 2000 4Runner. I'm not clear on the whole history of it but the latest is that a brand new OE exhaust system was installed by the dealer to the sum of $2200 to fix an emissions problem. The truck still fails the test with high NOX. There is no check engine light showing. Ideas?

I'm guessing an EGR problem like a sooted up valve but wouldn't that cause a P401 or 402? The catalytic converter prior to this one was an aftermarket one that was only in the truck for a few months. That cat was installed to address a check engine light but I don't know what the code was.

I was wondering what causes cat failure. I found several web ref's pointing to rich running engines ending in cat failure. I don't know whether the last cat on the truck was actually bad or just replaced because the dealer said to. Would an over-fueling situation cause a check engine light? - stuck or worn injector? If the fuel trim hit the end of its adjustment range, it throws a code right?

01-14-2011, 08:25 AM
Possible fuel pump is weak. Possible timing belt jumped due to lack of tension on the belt (caused by the water pump leaking on the tensioner piviot). A 2000 4runner did not have EGR.

NOX is caused by primarly lean conditions.

01-14-2011, 09:13 AM
I know that in my GM if the fuel trims go out of whack by more than something like 25% it throws codes... Cylinder bank 2 lean or cylinder bank 1 lean (P0171, P0174) for example. When my truck was running lean (bad fuel system setup) the Long Term fuel trims would creep up as it ran until eventually it would throw a code.

Can you see what the fuel trims are doing?

01-14-2011, 09:37 AM
I've seen it to the point that it was just a pinched signal wire on one of the O2's the graphs looked freaking perfect. But if you give her a bit of gas signal loss.
What typically causes cat faure is the wrong A/F ratio for a extended period o time. Make sure the check engine light works and is not just burnt out. (turn Key on, bulb check) it should light up I'd bulb is good. That will just eliminate the "check engine light is not on" because of a burnt bulb syndrome. :lmao:

Could always take to a second shop and not tell them ****. And see what they tell you. Between 2 estimates is going to be some sort of truth. (same parts needed)

but yes to much fuel, or to little fuel will fail a cat.

one atachment is a discription and how to diag a p0401
the other is how to diag a p0402
the 3rd is a list of each code
stright from toyota TIS

01-14-2011, 12:58 PM
Would a flaky O2 sensor wire cause a check engine light?

A weak fuel pump would be tested by measuring the pressure at the fuel rail, right?

01-14-2011, 01:04 PM
An oxygen sensor should set a check engine light. The computer should be able to see open circuts in that year. As a general rule, Oxygen sensors fail rich due to the low voltage input to the ECU.

You can check the fuel pressure where ever you have the ability to. I check it at the inlet fuel line. There is no schrader valve on the rail like you find on American vehicles.

01-14-2011, 01:10 PM
Having fought the high Nox battle with CAC with my FJ62. I suggest cutting to the chase and adding a couple bottles of isopropyl alcohol to a 1/4 tank of gas. Run it hot into the testing station on a quiet day when sitting in line is not required.

01-14-2011, 01:28 PM
Would a flaky O2 sensor wire cause a check engine light?

A weak fuel pump would be tested by measuring the pressure at the fuel rail, right?

I would notice that my fuel pressure would drop at higher RPM's/Load, so I only saw a drop in pressure when I put the Gauge on it and drove it.

Not saying that you wouldn't be able to diagnose any issues at idle, just that you may have to drive it. Does that truck have a vacuum line on the Fuel pressure regulator? Is it connected if so? If not that could be the source of some lean running.

01-14-2011, 01:53 PM
U can easily check the cat's operation by driving the car say home from work (just get it hot) then take a laser thermometer and test 2-6" in front of the cat and 2-6" behind the cat. There should be a 100 difference.

01-14-2011, 02:07 PM
Its already got a brand new cat on it so that's done. the owner of the truck is taking back to the dealer to complain about the lack of fix for the original problem. I was hoping to give him a list of things to have checked so that they can get to the root of the problem.

Thanks for all the responses so far.

01-14-2011, 06:01 PM
Hey Bruce is it only failing NOX? If the truck is running hot (IE bad thermostat or timing advanced to much) that will cause higher NOX's. NOX's increase as combustion temperatures rise.

01-18-2011, 05:07 PM
Any updates?