97singlecab

I've changed the vsv, modulator, vacuum hoses, egr valve and o2 sensors, still getting p0401.

Could my headers be causing a p0401? The headers were on the car when I bought it so I dont know exactly where they came from. The headers have a tag that says LCE engineering and that they are carb legal.

offset442

are you installing denso excact part replacements on the o2 sensors or you installing the after market ecu exploder that the parts counter guy said was cheaper or the "the right one for you meke/model"

if so go back to OEM exact part denso sensors. the bosh and other sensors will not work!!! they will cause the a/f ratio to be distorted and there fore the engine not to run properly and thus the computer sets the code...........

97singlecab

I got the denso sensor. I just changed my exhaust gasket and it didnt help either.

I really dont want to pay the dealer $100 to run diagnostics and tell me its the headers.

Is there a recommended toyota mechanic in the los angeles, west la, san fernando area?

offset442

ok lets go through this pice by pice

Open in EGR gas temp. sensor circuit - not checked
EGR gas temp sensor - not checked
Vacuum or EGR hose disconnected - dubble check
Open or short in VSV circuit for EGR - not checked
VSV for EGR - replaced?
sensor and ambient air temp. (2 trip detection logic) EGR t system
intake air sensor - not checked (is is reading -35 degrees f on a scan tool? )
EGR vacuum modulator -replaced
EGR valve stuck closed -replaced
ECM - not checked

ok you replaced the major parts of the egr system but did you ever check that they are actually working? you need to test for the electronic signals and make sure that they are accurate and functional, is the temperature sensor operating with its normal range, is the vsv turning on when its supposed to, the ecm is likely detecting an obvious numerical electrical fault if the code is set immediately, if it takes some larger amount of drive time if its a mechnical fault like a stuck value of vacuum problem

all the egr does is allow burned gas back into the system, so headers cannot be the problem unless the egr port is clogged or faked period end of story

97singlecab

I ohmd the egr temp sensor and it gave no reading. Im hoping thats my problem.

I just ordered one, will let you guys know if that fixes things.

97singlecab

Another question: where do you get the diagnostic procedure? I cant find the toyota fsm anywhere online.

I think it two years ago or so, i downloaded the fsm but it was lost when my old compuyer crashed and i cant find the fsm now anywhere.

tantacoma

Simply removing and cleaning my temp sensor fixed my P0401.
BTW, I used a metric flare wrench (like the ones that are used to remove hard brake lines) to remove it.

offset442

first not all temp sensors can be ohmed, some of them are thermocupples and generate voltage when heated, in the case with anything high temperature its like exhaust not going to be thermosistor but a thermocupple a thermosistor changes resistance with temperature, and thermocupple generates more voltage as it gets hotter and will ohm as a dead short cold, if it ohms as open circuit its probably bad, take a voltage reading cold, then take a voltage reading hot should see between 45 - 450 mv or 0.45 volts hot max

The list i gave is simple, when you look up the 401 code for you engine that the list of stuff that will cause it, that simple...............

btw replace the sensor its probably got an electrical fault from thermal cycling and when you disturbed it it "refreshed" the connections at the fault, its likely going to come back, just install a new sensor.

97singlecab

Oh boy do i feel like an asshole.

Went to the local pick-a-part, pulled an egr temp sensor from a 90's camry, and it took care of my egr problem. All it cost was $10. Before i went to teh pick-a-part, I called one of the toyota yards for an egr temp sesor and they quoted me $75, for a used one.


When i metered this new sensor, on the 2000 ohm setting i had no reading, on the 20k ohm setting i had a 3.xx reading. The manual says the sensor should meter at 600k ohm. My question is what did this new sensor actually meter at?

offset442

be careful if its the wrong resistance it will burn up the sensor input inside of the ecm. look's like your reading was 3 ohms i would guess that the sensor you have is a thermocupple which is basically 2 bits of bare wire twisted together and welded at the end, im not sure where this sensor is mounted but if its on the very hot gas intake from the exhaust manifold I would expect it to be such a sensor, if its somewhere else i would expect it to be a thermosistor and it shoud be in the 1-20 k ohm region heat it up sensor tip with a soldering iron 400-600 degrees there abouts and take the following measurements.

voltage cold, voltage hot if any

resistance cold / hot

you have to be careful just pulling random sensors off of other engines/vehicles they are not always the same...................and can / will damage the ecm