Recently bought a 00 SR5 w/3.4L, 173K miles from a friend. Check engine light on with codes for both O2 sensors. Replaced both O2 sensors with Bosch sensors (california emissions model) and the check engine light continues to stay illuminated. I have reset the OBD II codes using diagnostic tool and disconnected the pos battery terminal for abt 10 mins, both times the check engine lights come back on with the 2nd start. Codes P0141 and P0141 pending. A local mechanic told me before I replaced the sensors that it could take some time for the light to go off, as the computer has "learned" to stop recieving data from that sensor and has to r-learn to accept data from that sensor. Anyone have any experience with this? Any help would be GREATLY appreciated. Thanks!
Check Engine Light & P0141 After O2 Sensor Replacement
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HCurphy
New member
From the knowledge I have gained from these forums, I think your problem is the Bosch brand sensors. The consensus seems to be that Toyota's prefer the Denso sensors that they came with from the factory.
The Bosch seem to be hit or miss. If you could return the bosch and get denso that would most likely solve your problem. (check amazon-they have great prices on the denso sensors)
edit-also make sure you have the correct sensor.
The Bosch seem to be hit or miss. If you could return the bosch and get denso that would most likely solve your problem. (check amazon-they have great prices on the denso sensors)
edit-also make sure you have the correct sensor.
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Illicitdream
New member
Try this
Try cleaning your MAF sensor with some CRC MAF cleaner from an auto store... It cleared mine up at 175k and it still is going strong at 215k. Hope this helps!!,:guitar3:
Try cleaning your MAF sensor with some CRC MAF cleaner from an auto store... It cleared mine up at 175k and it still is going strong at 215k. Hope this helps!!,:guitar3:
T4R_Finally
New member
Use a scantool that will reset the code for you instead of pulling the battery cable. Make sure you got the right denso part number.
fenrisx
New member
I realize this thread is old, but I didn't want to create another on the same topic - figured this is more handy for people searching on Google as well (where I found this thread)..
On Saturday, I replaced the rear o2 sensor with the Denso OEM part. I then put about 60 miles on the 4Runner over the weekend and it ran great.
However, this morning I let the truck warm up a few minutes before leaving, and I could tell it was idling a little rough occasionally. When I left to drop my kids off at school it starting exhibiting the same symptom it had before replacing the o2 sensor that was throwing the P0141 code -- basically it was barely running at all - surges of very very little power to no power. I pulled off the road into a neighborhood, and after a couple of minutes it started running fine again. In the parking lot at their school it died while idling in Park. But started right up, and ran fine all the way back to my house.
TL;DR - Replaced o2 sensor with new Denso sensor, but didn't seem to fix the issue.
Is bad o2 sensor or bad wiring/ECM issue really the only two causes for P0141? Nothing else up stream that would cause P0141? Could a bad/clogged cat cause this? I'm thinking this might turn into a costlier fix than I'd like!
I thought maybe it was rusted/corroded through and moisture might be getting in on the o2 sensor, but I don't see any exhaust leaking from this area at all..[picture is pre-replacement..]
(FWIW: 2000 3.4L 4WD with 270k miles)
Thanks!
On Saturday, I replaced the rear o2 sensor with the Denso OEM part. I then put about 60 miles on the 4Runner over the weekend and it ran great.
However, this morning I let the truck warm up a few minutes before leaving, and I could tell it was idling a little rough occasionally. When I left to drop my kids off at school it starting exhibiting the same symptom it had before replacing the o2 sensor that was throwing the P0141 code -- basically it was barely running at all - surges of very very little power to no power. I pulled off the road into a neighborhood, and after a couple of minutes it started running fine again. In the parking lot at their school it died while idling in Park. But started right up, and ran fine all the way back to my house.
TL;DR - Replaced o2 sensor with new Denso sensor, but didn't seem to fix the issue.
Is bad o2 sensor or bad wiring/ECM issue really the only two causes for P0141? Nothing else up stream that would cause P0141? Could a bad/clogged cat cause this? I'm thinking this might turn into a costlier fix than I'd like!
I thought maybe it was rusted/corroded through and moisture might be getting in on the o2 sensor, but I don't see any exhaust leaking from this area at all..[picture is pre-replacement..]
(FWIW: 2000 3.4L 4WD with 270k miles)
Thanks!
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onemanarmy
Member
SO I'm now dealing with the same issue. on my 96 5speed, getingt a P0141, replaced the rear sensor with a Denso, code came right back. Cleaned the MAF, code came right back.
I checked the resistance of the heater circuit of the new O2 sensor, and that was within spec, so I moved onto checking the ECM...but its kind of confusing, to me anyway.
So, per the FSM, can only be two more things to check....bad connection in the harness, or a bad ECM.
When checking the ECM, do I leave the connector attached (plugged into the ECM)? I think I read in the FSM to leave the connectors plugged in. Or do I unplug it and test the ECM connectors? Does it matter? Do I touch the red connector of my volt meter to 'HT2' and the black connector to a body ground....for sensor 2? I don't have a fancy data logger, so I can't see whats going on in real time, but the trouble shooting steps seem pretty straight forward. The code comes back at the same point in my commute drive everyday.
Also, is there a way to see what the O2 sensor heater current is when the heater is operating? Guess I'd need a nice scanner for that.
Finally, the FSM states that the voltage is 'OK' at 9-14V when testing the ECM, but if it checks 'OK', to replace the ECM. Am I reading that right? Seems odd.....nothing is 'OK' if the ECM needs to be replaced.
Thanks for any insight.
I checked the resistance of the heater circuit of the new O2 sensor, and that was within spec, so I moved onto checking the ECM...but its kind of confusing, to me anyway.
So, per the FSM, can only be two more things to check....bad connection in the harness, or a bad ECM.
When checking the ECM, do I leave the connector attached (plugged into the ECM)? I think I read in the FSM to leave the connectors plugged in. Or do I unplug it and test the ECM connectors? Does it matter? Do I touch the red connector of my volt meter to 'HT2' and the black connector to a body ground....for sensor 2? I don't have a fancy data logger, so I can't see whats going on in real time, but the trouble shooting steps seem pretty straight forward. The code comes back at the same point in my commute drive everyday.
Also, is there a way to see what the O2 sensor heater current is when the heater is operating? Guess I'd need a nice scanner for that.
Finally, the FSM states that the voltage is 'OK' at 9-14V when testing the ECM, but if it checks 'OK', to replace the ECM. Am I reading that right? Seems odd.....nothing is 'OK' if the ECM needs to be replaced.
Thanks for any insight.
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Yes you check it with the connector connected to the ecu, you are basically checking that you are getting power from the efi relay through the sensor to the ecu. yes the red lead goes to the ht2 and the black to body ground. if you do it backwards you'll just get a negative voltage reading. the check engine light comes on at the same point in your commute due to the drive cycle meeting the criteria needed for the ecu to run monitor.
onemanarmy
Member
Thanks.
Yea, it s a '2 drive cycle' code, and it does exactly that. 2 drive cycles and about 8 miles and its back on.
Would it be possible to wire up the O2 to switch it on and off manually when I first crank the engine? I could leave it on for about 5-10 minutes into a drive , and that should mimic what the computer is supposed to be doing. Just for troubleshooting purposes, and to make sure the wiring harness is OK and there isn't a break anywhere.
Yea, it s a '2 drive cycle' code, and it does exactly that. 2 drive cycles and about 8 miles and its back on.
Would it be possible to wire up the O2 to switch it on and off manually when I first crank the engine? I could leave it on for about 5-10 minutes into a drive , and that should mimic what the computer is supposed to be doing. Just for troubleshooting purposes, and to make sure the wiring harness is OK and there isn't a break anywhere.
onemanarmy
Member
So I checked the ECM, get 0 volts from the bank 2 connector with the key on. According to the FSM, that is acceptable and the ECM should be operating properly.
To add to my confusion, I checked the bank 1 connector, and got 12 volts, which points to an ECM malfunction, but I'm not getting a P0135 (front O2 issue) code.
Am I looking at the FSM wrong? I would think that 9-14 volts output with the key on would be the correct operation? With the key on, shouldn't voltage be sent by the ECM to the O2 heater? With the key on, I get 12 volts from the front O2 heater connection and 0 volts from the rear O2 heater connection (at the ECM).
Also checked voltage at the connectors with the engine on....get 0.24 volts for the front O2 and still 0 volts for the rear O2.
Rechecked the resistance at the rear O2 again, and that is within spec.
Wanted to check the wiring, so I applied 12 volts from the battery directly to the rear O2 heater circuit with the connector disconnected from the ECM. Measured the voltage at the rear O2 and am getting a constant 4.9 volts. Why would that be? Is there a circuit where the voltage is manipulated? Does the O2 heater operate on 5 volts vs 12 volts?
All of this is leading me to believe the ECM is faulty.....thoughts?
I'd replace it just to check, but manual trans ECMs are way more expensive and rare compared to AT versions, so I'm hesitant.
To add to my confusion, I checked the bank 1 connector, and got 12 volts, which points to an ECM malfunction, but I'm not getting a P0135 (front O2 issue) code.
Am I looking at the FSM wrong? I would think that 9-14 volts output with the key on would be the correct operation? With the key on, shouldn't voltage be sent by the ECM to the O2 heater? With the key on, I get 12 volts from the front O2 heater connection and 0 volts from the rear O2 heater connection (at the ECM).
Also checked voltage at the connectors with the engine on....get 0.24 volts for the front O2 and still 0 volts for the rear O2.
Rechecked the resistance at the rear O2 again, and that is within spec.
Wanted to check the wiring, so I applied 12 volts from the battery directly to the rear O2 heater circuit with the connector disconnected from the ECM. Measured the voltage at the rear O2 and am getting a constant 4.9 volts. Why would that be? Is there a circuit where the voltage is manipulated? Does the O2 heater operate on 5 volts vs 12 volts?
All of this is leading me to believe the ECM is faulty.....thoughts?
I'd replace it just to check, but manual trans ECMs are way more expensive and rare compared to AT versions, so I'm hesitant.
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CESwartz07
New member
Couldn’t it just mean the cat converter is bad?
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onemanarmy
Member
I don't THINK so, but not 100%.
The P0141 code is related to the heater circuit of the O2 sensor (takes too long to heat up) and not related to any exhaust reading while the engine is running, from my understanding.
There are other trouble codes that relate to incorrect emission readings.
Only three repair options for this, per the FSM.
I replaced the O2 and checked the heater circuit resistance....all good.
I'm getting no voltage out of the ECM rear sensor heater circuit with the key on (also no voltage with the engine running) but get 12 V out of the ECM to the front circuit when the key is on (not running)....which makes me believe the ECM is bad, but I'm confused by the FSM wording. Also, when searching on this site, most mention that the ECM very rarely fails...adding pause to replacing the ECM, but I'm not sure of the accuracy of that statement.
Then, today, I put 12V through the rear O2 heater circuit, but get a 5V reading at the sensor...is it supposed to be stepped down like that? I don't think it is, as I've seen a site where they splice in a 12V incandescent bulb to know exactly when the heater is coming on. You'd need 12V for that.
Again, the scarcity and price of 5 speed ECMs is not helping the issue either.
Thanks
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DaMonkey
New member
For some reason, I'm thinking that 3rd gen 4runners were split where earlier 3rd gens are narrow-band, and later were wide-band, but I'm not sure. I am sure that there are several different potential part numbers for o2 sensors and I've seen a lot of misinformation from 3rd party suppliers. For instance, Amazon will steer you wrong based on car info. The Denso part number search seems to be a safe place to be sure you have the right sensor installed?
Whether it's wideband or not, the return signal to ECU will not exceed 5v. 0-5v is typical signal range to send back to ECU.
Whether it's wideband or not, the return signal to ECU will not exceed 5v. 0-5v is typical signal range to send back to ECU.
onemanarmy
Member
To clarify...I put 12V FROM the ECM connector TO the O2 sensor connector....Tested at sensor end (disconected from sensor) and didn't get 12V. Seemed odd to me. Was not looking for the return to ECM voltage.
I got the P/N from the Denso site, and that's the one I used.
Thanks
onemanarmy
Member
Does anyone have the ECM pin schematics for all the 3rd gen (with manual trans) years?
thinking about trying a new ECM, however I know that there are wiring changes between some years, but do not know the extent. Wondering if a 1997 or 1998 ECM would work on my 1996. Doubtful, but not sure.
Thanks
thinking about trying a new ECM, however I know that there are wiring changes between some years, but do not know the extent. Wondering if a 1997 or 1998 ECM would work on my 1996. Doubtful, but not sure.
Thanks
19963.4lsr5
New member
What FSM are you using to trouble shoot? Your 96 is a narrow band sensor.
Pull your o2 sensor apart and look for corrosion in the wiring. I have a 97 wiring book and thanks to Durk a 97 wiring PDF as well. I'll take a gander at work this evening.
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TheDurk
Elite Member
Huh? On mine, the ECM connection gives ground, and the 12V+ comes in on the other leg straight from the fuse.
2nd question. Are you still connected at the ECM end when you tried whatever you tried? Because that sounds like a short through the ECM to me (ungood).
19963.4lsr5
New member
Check Engine Light & P0141 After O2 Sensor Replacement
With engine running you should be able to probe the back side of the HT2 pin (red with white) If you read 12v it looks like the transistor that provides the ground to energize the heater circuit is burned open.
If instead you read 0v pull the sensor connector off and look for 12v on the B+ terminal (white with blue). Also try and measure continuity between the HT pin in the sensor connector and the HT2 pin of the ECU.
If you have something in between like 5v there is some sort of path to ground and your reading the voltage drop across the heater element.
If you indeed have a bad transistor in the ECU you could wire a relay up that will be energized when the EFI relay is energized and ground the HT wire through the relay you installed. Extract the wire from the ECU connector.
I'm still looking at things but this is a start.
Edit. If they are measuring heater element amps in a 96 ECU to determine proper heater operation rather than the typical how long it takes till a valid sensor signal is present then that 96 ECU is pretty advanced for that area.
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With engine running you should be able to probe the back side of the HT2 pin (red with white) If you read 12v it looks like the transistor that provides the ground to energize the heater circuit is burned open.
If instead you read 0v pull the sensor connector off and look for 12v on the B+ terminal (white with blue). Also try and measure continuity between the HT pin in the sensor connector and the HT2 pin of the ECU.
If you have something in between like 5v there is some sort of path to ground and your reading the voltage drop across the heater element.
If you indeed have a bad transistor in the ECU you could wire a relay up that will be energized when the EFI relay is energized and ground the HT wire through the relay you installed. Extract the wire from the ECU connector.
I'm still looking at things but this is a start.
Edit. If they are measuring heater element amps in a 96 ECU to determine proper heater operation rather than the typical how long it takes till a valid sensor signal is present then that 96 ECU is pretty advanced for that area.
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