I have a 1998 limited 3.4L, the engine light came on, pulled two codes ( p0125 & p0171) cleared both codes. Drove vehicle light came back on once closed loop occurs, ohmed out A/F sensor found it to be bad. Replaced sensor with Bosch sensor and code p0171 went away but p0125 still there. Hooked up my laptop to vehicle to read output voltage from sensor #1, I'm getting no voltage reading from #1 sensor but can get a voltage reading from #2 sensor. I checked for open/short in the brown & the white wire in harness from sensor to ECU, both check out good. Any ideas much appreciated. Thank you in advance, Brian
code p0125
- Thread starter weezin355
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techno
New member
From the manual. This may help you or may confuse you....
P0125 Detecting Condition
After engine is warmed up, heated oxygen sensor (bank1 sensor 1) output does not indicate RICH (< or = 0.45 V)even once when conditions (a), (b), (c) or (d) continue for at least 1.5 mins:
(a) Engine speed: 1,500 rpm or more
(b) Vehicle speed: 25 <or= SPD and 62 MPH
(c) Throttle valve does not fully closed
(d) 140 sec. or more after starting
Trouble Area
Open or short in heated oxygen sensors (bank1 sensor 1) circuit.
Heated oxygen sensor (bank 1 sensor 1).
Air induction system.
Fuel pressure.
Injector.
Gas leakage on exhaust system.
ECM
If the voltage output of the heated oxyxgen sensor is less than 0.1 V, heated oxygen sensor circuit may be open or short.
Trouble shooting Procedure.
(a)Connect the OBD II scan tool or toyota hand held tester to the DLC3
(b) warm up the engine to normal operating temp
CHECK
Read the voltage output of the heated oxygen sensor when the engine is suddenly raced. (Perform quick racing to 4000 rpm 3 times.
Does heated oxygen sensor output a RICH signal (0.45 V or more) at least once?
P0125 Detecting Condition
After engine is warmed up, heated oxygen sensor (bank1 sensor 1) output does not indicate RICH (< or = 0.45 V)even once when conditions (a), (b), (c) or (d) continue for at least 1.5 mins:
(a) Engine speed: 1,500 rpm or more
(b) Vehicle speed: 25 <or= SPD and 62 MPH
(c) Throttle valve does not fully closed
(d) 140 sec. or more after starting
Trouble Area
Open or short in heated oxygen sensors (bank1 sensor 1) circuit.
Heated oxygen sensor (bank 1 sensor 1).
Air induction system.
Fuel pressure.
Injector.
Gas leakage on exhaust system.
ECM
If the voltage output of the heated oxyxgen sensor is less than 0.1 V, heated oxygen sensor circuit may be open or short.
Trouble shooting Procedure.
(a)Connect the OBD II scan tool or toyota hand held tester to the DLC3
(b) warm up the engine to normal operating temp
CHECK
Read the voltage output of the heated oxygen sensor when the engine is suddenly raced. (Perform quick racing to 4000 rpm 3 times.
Does heated oxygen sensor output a RICH signal (0.45 V or more) at least once?
The problem I was having was that I didn't have any output voltage from a/f sensor. I tried the original toyota/denso a/f sensor again, which I had just replaced with a Bosch one. It acted the same (no voltage output) with either sensor. I looked for the harness rubbing up to the firewall and from the firewall to ECU. In moving wires and watching laptop hooked to DLC3 I noticed a voltage signal. As for right now no codes are present.
Thank you
Thank you
silver2000runner
New member
p0125 / relating to bank 1 sensor 1 O2 sensor ...
Please assist if possible...
I had my clutch changed on my 2000 4x4 3.4L 5spMan 4runner SR5 and upon picking the car up found MIL - code p0125 - that would not clear. I ****ed around with coolant system research and sensor repairs for several months and got lazy - accepting the 2mpg loss of efficiency.
Now I can't pass inspection with the light on and it's got to get fixed.
I found that my clutch mechanic must have damaged the wiring harness on O2 sensor B1S1. Looking under the vehicle I found one of the 4 wires to B1S1 sensor connection broken. I soldered this back together - cleared the code - code reappeared.
I have confirmed 0.0 volts on B1S1.
I have switched O2 sensor locations on the car to see if the 0.0vdc measurement would move to B1S2 (indicating a bad sensor).
ODBII scanner still indicated 0.0vdc on B1S1, indicating open or short still occuring on B1S1 harness or connector.
This pointed me back to the known damage to wiring harness found following clutch change.
I tested each of the B1S1 connector wires for continuity through the damaged/repaired section of the harness. All good !!! ???
I have not tried to measure any voltage on the connector with the car running (heater voltage, gnd, closed loop control voltage). I suppose that would be my next step.
Am I on the right track or is there something easy that I am missing?
Is my ECM blown?
How can I test my ECM to know without buying a replacement?
Please assist if possible...
I had my clutch changed on my 2000 4x4 3.4L 5spMan 4runner SR5 and upon picking the car up found MIL - code p0125 - that would not clear. I ****ed around with coolant system research and sensor repairs for several months and got lazy - accepting the 2mpg loss of efficiency.
Now I can't pass inspection with the light on and it's got to get fixed.
I found that my clutch mechanic must have damaged the wiring harness on O2 sensor B1S1. Looking under the vehicle I found one of the 4 wires to B1S1 sensor connection broken. I soldered this back together - cleared the code - code reappeared.
I have confirmed 0.0 volts on B1S1.
I have switched O2 sensor locations on the car to see if the 0.0vdc measurement would move to B1S2 (indicating a bad sensor).
ODBII scanner still indicated 0.0vdc on B1S1, indicating open or short still occuring on B1S1 harness or connector.
This pointed me back to the known damage to wiring harness found following clutch change.
I tested each of the B1S1 connector wires for continuity through the damaged/repaired section of the harness. All good !!! ???
I have not tried to measure any voltage on the connector with the car running (heater voltage, gnd, closed loop control voltage). I suppose that would be my next step.
Am I on the right track or is there something easy that I am missing?
Is my ECM blown?
How can I test my ECM to know without buying a replacement?
techno
New member
Here's the full page for the FSM diagnostic procedure, this might help a little more. http://www.ncttora.com/fsm/1996/SIL/techinfo.toyota.com/ileaf/02toyrm/02toypdf/02rmsour/2002/024runne/di/eg5vzfe/cip0125o.pdf
Everything you described sounded reasonable and I think you're on the right track.
Everything you described sounded reasonable and I think you're on the right track.
silver2000runner
New member
This is good info - thank you very much.
Wish I had just kept the vehicle with me thru the weekend and utilized this info. I made the mistake of bringing to another shop that insisted the temperature sensor was bad. After I took the car back from them, I noticed after 15 minutes of driving that now my idle is racing - up around 1900+.
When I called them back to ask what they did to the idle, they said "it came in that way."
#$%^!!
Wish I had just kept the vehicle with me thru the weekend and utilized this info. I made the mistake of bringing to another shop that insisted the temperature sensor was bad. After I took the car back from them, I noticed after 15 minutes of driving that now my idle is racing - up around 1900+.
When I called them back to ask what they did to the idle, they said "it came in that way."
#$%^!!
silver2000runner
New member
How accurate are the ECU pin numbers in this document for yr2000 4runner 4x4 sr5 3.4L? For example...
1 - The documentation wiring diagram only shows one O2 sensor and it happens to be O2S (bank 2). Sensor pin 3 (OXS) connects to block E9 pin 27, but dwg in .http://www.mr2.com/files/mr2/techinfo/Wiring Diagrams/5VZ-FE/4Runner/2000 4Runner.pdf shows this Sensor pin 3 connecting to block E12 pin 8.
2 - Wire color codes do not match the codes shown in the mr2 link.
3 - It seems that there is some confusing info about how ECMs are pinned out for different models. How will I know what pins on my ECM do what?
White00SR5
New member
Hi, sorry to dig up an old thread but I cant post a thread because I'm too new.
Ive had a rough go with the exhaust system lately and had one more pop up….
I had a P0420 code. My cat and pipe was in pretty rough shape so I figured id just replace it with an aftermarket one instead of trying to chase the code down. So I replaced the cat with a new aftermarket cat and replaced the fwd o2 sensor because it had become one with the pipe.
A day of driving and I now have P0125. From reading things it seems like its almost never the coolant/fuel system and o2 sensors instead. With recent exhaust work it makes me nervous I screwed something up.
Since my o2 sensors are both the same on the non cali 2000 I swapped them and cleared the code and as soon as it warms up the cel comes back on with the same code. This is a freeze frame of when the the cel comes on. Coolant temp is aprox 190 degrees so its safe to assume its not a thermostat or ect since it is reaching the appropriate temp?
Ive had a rough go with the exhaust system lately and had one more pop up….
I had a P0420 code. My cat and pipe was in pretty rough shape so I figured id just replace it with an aftermarket one instead of trying to chase the code down. So I replaced the cat with a new aftermarket cat and replaced the fwd o2 sensor because it had become one with the pipe.
A day of driving and I now have P0125. From reading things it seems like its almost never the coolant/fuel system and o2 sensors instead. With recent exhaust work it makes me nervous I screwed something up.
Since my o2 sensors are both the same on the non cali 2000 I swapped them and cleared the code and as soon as it warms up the cel comes back on with the same code. This is a freeze frame of when the the cel comes on. Coolant temp is aprox 190 degrees so its safe to assume its not a thermostat or ect since it is reaching the appropriate temp?
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spartacus
Senior Member
Bank 1 sensor 1 is below 0.1V indicating an open or short in the system. Also the replacement sensor should be Denso or oem.
White00SR5
New member
Yea they are denso 234-4162.
Short in the system….So Im tracking down an electrical error in the wiring harness between the o2 sensor and ecu correct?
Short in the system….So Im tracking down an electrical error in the wiring harness between the o2 sensor and ecu correct?
spartacus
Senior Member
Yeah, I was going by what was said in the earlier post. Do you have access to the fsm. If not I can post the trouble shooting pages.
White00SR5
New member
I dont have the service manual, any info would be awesome! Thanks!
spartacus
Senior Member
Using your obd when you punch the gas pedal the bank 1 sensor 1 should fluctuate between 0.1V to 0.9 volts. If it's not then there is a problem with the o2 sensor.
White00SR5
New member
Ok thanks, Ill check that in an hour. I doubt its a problem with the actual sensor since I swapped it with the rear one and the code came back on. Ill check voltage and see. Sounds likeIll be chasing a wiring issue
White00SR5
New member
Looks like it is fairly stuck at 0.0. Its a different sensor than yesterdays screen shots and it looks to be putting out the same voltage. So Im guessing there is a wiring issue. It did bump to life momentarily but died back to 0 right away.
Attachments
spartacus
Senior Member
you are correct most likely a wiring issue.