cordrayj1

I have 2 codes that are shown on this chart. which bothers me.

it says:

"P0135/P0141

For Fail-Safe Operation: the heater circuit in which an abnormality is detected is turned off.

Fail-Safe Deactivation Conditions: ignition switch off"


so does this mean that my O2 sensors have been completely disabled by the ECM?


i have other codes as well. that are directly related. i have to replace ALL of my o2 sensors as of now. and work on the LEAN FUEL MIXTURE issue which is P0171 (im missing one of the 2 rubber caps that goes on the 2 vacuum fittings on the very top of the engine) . . . from what i have read i will be able to just plug that up and should take care of the lean mixture issue.

BajaRunner

Sounds like you may have a wiring problem. Have you gone underneath the truck and checked to make sure that the wiring harness to the O2 sensors is not disconnected, cut or burnt? Very rarely would both O2 sensors go out, and throw those codes unless a harness came undone or was damaged. Also, did you use a ohm meter and test the resistance across the heater circuit? Its real easy. I doubt that the O2 sensors are your problem, more likely the wiring but you should check just in case.

Check all grounds, and somehow the ground that goes on the intake plenum coming off the diagnostics box in the engine bay will throw this code, as well as others.

cordrayj1

ive never touched any of those things on my vehicle. whether or not my mechanic has, im not sure of that. he is a 25+ year master tech that ONLY works on Lexus-Toyota. so he knows what he's doing. thanks for the info, ill check on those wires. they are prob hangin w no connections by now. Thanks again.

BajaRunner

Well I doubt it was done maliciously. A perfectly placed rock, or something could have hit the wiring connections, or the wire may have melted on the exhaust pipe. I'm not really sure, but its always easy to start out with the simple possibilities first, then we'll move onto the other stuff.

waskillywabbit

iTrader: (-1)

:wabbit2:

TheDurk

To answer your original question, the answer is yes--the ECU is running without input from the sensors. This is called 'open loop' mode, where the ECU guesses at the correct timing/mixture but does not get any feedback from the front sensor as to how ell it did so that it can adjust trim. You can disregard the rear sensor, as all it does is set codes.

The engine will always run in 'open loop' at start-up and until temps are up to normal. The mixture will be richer than it would be in closed-loop with an operating sensor, with adverse impact on performance and fuel economy, and the long-term risk of over-heating and damaging your cat(s) if running in 'open-loop' full time.