onemanarmy
Member
This is my concern. Sounds like the wire may be partially grounding somewhere?
Nest step is to manually ground it with a switch in the cab and drive around and see if the CEL turns off.
Check Engine Light & P0141 After O2 Sensor Replacement
- Thread starter aghutter
- Start date
This is my concern. Sounds like the wire may be partially grounding somewhere?
Nest step is to manually ground it with a switch in the cab and drive around and see if the CEL turns off.
onemanarmy
Member
So I cut the wire on the O2 sensor that grounds the circuit and added a dedicated wire grounded directly to the battery. I turned the key on and the sensor got too hot to hold in 2 minutes.
Reinstalled the sensor with the dedicated ground wire, cleared the code, and drove. CEL came back on.
So, now....I'm still getting the P0141, heater circuit malfunction, code. However, the sensor heats up quickly, but with the computer bypassed for this operation.
I was hypothesizing that the other two signal wires would send the temp info back to the computer, as well as the exhaust reading. Or, is the computer getting the temp info back via some other method?
With proper computer operation, I don't know how long the O2 sensor is supposed to stay on, what temp it gets to, and what wire sends the feedback to the computer to confirm that it indeed got hot in the specified amount of time.
Any ideas?
Thanks
Reinstalled the sensor with the dedicated ground wire, cleared the code, and drove. CEL came back on.
So, now....I'm still getting the P0141, heater circuit malfunction, code. However, the sensor heats up quickly, but with the computer bypassed for this operation.
I was hypothesizing that the other two signal wires would send the temp info back to the computer, as well as the exhaust reading. Or, is the computer getting the temp info back via some other method?
With proper computer operation, I don't know how long the O2 sensor is supposed to stay on, what temp it gets to, and what wire sends the feedback to the computer to confirm that it indeed got hot in the specified amount of time.
Any ideas?
Thanks
TheDurk
Elite Member
Why would you think the ECM is getting temp info? I'm pretty sure it just monitors the current flow through the sensor heater when it is operating. Why do I think that? Because that's what the manual says:
The ECM is what decides when the heater operates based on the coolant temp input it gets from the ECT. It does not gather data on O2 sensor temp, period.
I really don't know what you have been hoping to achieve. The only way that code is going away is if the ECM heater circuit behaves the way the ECM expects it to. Wiring the sensor heater in some other way might make the engine run, but I doubt it. You are probably stuck in Open Loop as long as the ECM thinks the heater is busted, so anything you do will have zero effect on anything, until you fix the heater circuit through the ECM the way it is supposed to be. If the ECM thinks the heater is bad, it disregards any signal it gets from that sensor as spurious and just uses its stored maps.
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onemanarmy
Member
Thanks.
I'm trying to troubleshoot, that's what I'm doing.
Per the FSM troubleshooting, there are 3 things it could be.
1. I've replaced the sensor (correct denso part) and verified it gets hot
2. I've not replaced the ECM, as you can imagine, a 1996 V6 5 speed ECM is not easy to find, and who knows what shape a used one is
3. I've seen some odd Ohm readings on the grounding wire, however the CEL just randomly came on one day, the truck and all wiring is stock, so I'm not convinced the wire would just short out one day (but crazy things happen). It would take a full gut of the truck to trace that wire. I've tested the front O2 sensor circuit, and get the same voltage readings at HT1 and HT2 with the key on, but just getting the rear code. This SHOULD indicate that the front and rear sensors are 'grounded' when key on. Clear as mud.
I've seen some 'rebuilt' ECMs on Ebay....may try that first.
Thanks
I'm trying to troubleshoot, that's what I'm doing.
Per the FSM troubleshooting, there are 3 things it could be.
1. I've replaced the sensor (correct denso part) and verified it gets hot
2. I've not replaced the ECM, as you can imagine, a 1996 V6 5 speed ECM is not easy to find, and who knows what shape a used one is
3. I've seen some odd Ohm readings on the grounding wire, however the CEL just randomly came on one day, the truck and all wiring is stock, so I'm not convinced the wire would just short out one day (but crazy things happen). It would take a full gut of the truck to trace that wire. I've tested the front O2 sensor circuit, and get the same voltage readings at HT1 and HT2 with the key on, but just getting the rear code. This SHOULD indicate that the front and rear sensors are 'grounded' when key on. Clear as mud.
I've seen some 'rebuilt' ECMs on Ebay....may try that first.
Thanks
TheDurk
Elite Member
If I were in your shoes, I'd do a de novo two-wire run from the ECM to the sensor, at least as a test. No need to gut the truck to do that.
onemanarmy
Member
Update:
So I tested the FRONT O2 sensor, and it does not get hot (or even warm) with the key on.
I then used an alligator clip to run a wire from HT2 on the ECM directly to the grounding wire of the rear O2 sensor and got no heat from the sensor with the key on.
These 2 things are leading me to believe the ECM is bad.
So I tested the FRONT O2 sensor, and it does not get hot (or even warm) with the key on.
I then used an alligator clip to run a wire from HT2 on the ECM directly to the grounding wire of the rear O2 sensor and got no heat from the sensor with the key on.
These 2 things are leading me to believe the ECM is bad.
19963.4lsr5
New member
If you got no heater grounding the HT2 wire at the pcm to me there is something wrong with the wiring or connectors crimped to the wire. Power comes from a relay. You proved there is 12v at the power side of the sensor connector at key on.
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onemanarmy
Member
So the power comes from a relay, and I've verified that the sensors will get hot with dedicated ground wire and the key on.
The computer 'grounds' the circuit with the HT1 and HT2 pins, correct? So if the sensors aren't getting hot, that is either a bad ECM or a cut wire between the ECM and sensor, correct?
The rear sensor still did not get hot with a dedicated wire hooked to HT2 and the sensor, bypassing factory wiring on that circuit.
It's odd that both sensors would be exhibiting the same symptoms.
The computer 'grounds' the circuit with the HT1 and HT2 pins, correct? So if the sensors aren't getting hot, that is either a bad ECM or a cut wire between the ECM and sensor, correct?
The rear sensor still did not get hot with a dedicated wire hooked to HT2 and the sensor, bypassing factory wiring on that circuit.
It's odd that both sensors would be exhibiting the same symptoms.
19963.4lsr5
New member
Measure the resistance with an ohm meter between the HT2 at the ECU and the pin it goes to at the O2 sensor. I’m betting it’s high. You sent 12v on the wire in the beginning of all this and only seen 5v at that wire at the connector for the sensor.
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onemanarmy
Member
measured on 12/2/18.....saw 16 Ohms
TheDurk
Elite Member
No, if the ECM is getting false inputs (say from a bad MAF) that say the sensors don't need added heat, it won't provide the ground to the heater filament thinking it is doing the right thing.
onemanarmy
Member
Interesting.
That is not a trouble area for this code, per the FSM. I've cleaned my MAF also, however.
I still don't know when the O2 sensor is supposed to get hot (based off ambient temp or every cold start?), does it get the same temp everytime, how quickly should it heat up to satisfy the ECM, and how long does the O2 sensor heater stay activated? I think the ECM detects the current flow to on the circuit, so it assumes if current is flowing, the heater is working. I also assume its on for a pre-determined time period and then turns itself off, since there is no temperature feedback to the ECM. This makes me think that the sensor should get hot via the 12V at every key on cycle, regardless of other conditions.
So is it 'bad' that I took both O2 sensors out of the exhaust pipe, turned the key on, and neither got hot? Are there a variety of other parameters that would tell the sensors to heat up or not?
That is not a trouble area for this code, per the FSM. I've cleaned my MAF also, however.
I still don't know when the O2 sensor is supposed to get hot (based off ambient temp or every cold start?), does it get the same temp everytime, how quickly should it heat up to satisfy the ECM, and how long does the O2 sensor heater stay activated? I think the ECM detects the current flow to on the circuit, so it assumes if current is flowing, the heater is working. I also assume its on for a pre-determined time period and then turns itself off, since there is no temperature feedback to the ECM. This makes me think that the sensor should get hot via the 12V at every key on cycle, regardless of other conditions.
So is it 'bad' that I took both O2 sensors out of the exhaust pipe, turned the key on, and neither got hot? Are there a variety of other parameters that would tell the sensors to heat up or not?
TheDurk
Elite Member
I didn't make that up about the MAF. From the 2000 EWD:
I also wasn't talking about your code. I was answering your question, which is different from analyzing your code.
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JoanneFelix
New member
1999 4runner
Hi there, I am new to the forum so I apologize if I am not supposed to be asking questions first. I could really use someone to help me with this. I have a 1999 4RUNNER the engine light is on, when the mechanic put the diagnostic tool on the only thing that came up was a code stating that the diagnostic tool was on. So the eraser the check engine light. I took it in for smog and it failed for the first time ever, they said it only failed because either the battery had recently been disconnected or someone cleared the check engine light. They told me to drive it for 30 to 50 miles and that should reset the computer, so I did and guess what the check engine light reappeared. I took it back to the smog shop and guess what if the check engine light is on it is automatic FAIL. I have had two different shops put the diagnostic tool on and NOTHING, no codes. I am not made of money, like most of us. Please help what could be wrong? I am so lost and I desperately need my baby back!
Hi there, I am new to the forum so I apologize if I am not supposed to be asking questions first. I could really use someone to help me with this. I have a 1999 4RUNNER the engine light is on, when the mechanic put the diagnostic tool on the only thing that came up was a code stating that the diagnostic tool was on. So the eraser the check engine light. I took it in for smog and it failed for the first time ever, they said it only failed because either the battery had recently been disconnected or someone cleared the check engine light. They told me to drive it for 30 to 50 miles and that should reset the computer, so I did and guess what the check engine light reappeared. I took it back to the smog shop and guess what if the check engine light is on it is automatic FAIL. I have had two different shops put the diagnostic tool on and NOTHING, no codes. I am not made of money, like most of us. Please help what could be wrong? I am so lost and I desperately need my baby back!
onemanarmy
Member
Well that is interesting. From what you say, the engine should be running to get accurate O2 sensor test results? As there would be no air volume moving with just the key on.
However, per my 96 FSM, it states to test the O2 sensor functions and ECM outputs with just the key on, does not state that the engine should be running.
Again, per my 1996 FSM, there are only 3 things that could cause the P0141 code, and MAF/air volume is not one of them. Is the 2000 ECM wired differently? I'm not clear on how intake air volume and exhaust temp is correlated?
In trying to understand if I'm dealing with a ECM or wiring issue, I took both O2 sensors out (on a cold engine) and turned the key on, and neither got hot or even warm. Should they?
Thanks for your help.
19963.4lsr5
New member
19963.4lsr5
New member
The basic operational theory could be the same from your 96 to the 2000 but the ECMs have improved so much every year since obdii got implemented that their basic control of certain functions became more complex as capability’s improved. Or a better technical writer wrote the 2000 FSM and included more info.
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Have you found a solution yet? I have the same exact problem. Originally had the P0171 and P0141code and did MAF and O2 sensors. Then I plug in the Underdog O2 simulator and still get the PO141. I may have to look for a referal to a shop around Philly next.
onemanarmy
Member
I have not found a solution yet.
I'm thinking either a bad ECM or somehow the wiring between the ECM and the sensor has become compromised. However, I've not messed with any wires and my 4 runner is stock.
I've yet to fully understand when and for how long the sensors are 'heated'.
I plan on doing some more troubleshooting this weekend.
I'm thinking either a bad ECM or somehow the wiring between the ECM and the sensor has become compromised. However, I've not messed with any wires and my 4 runner is stock.
I've yet to fully understand when and for how long the sensors are 'heated'.
I plan on doing some more troubleshooting this weekend.
Update on mine, I bought the Underdog O2 simulator and installed on the rear. Still have the same faults. Shop said it could be the front O2 sensor even though it states bank2. I’m going to switch the simulator to the front tonight. I’m thinking it could be the cats bc I replaced them w those Chinese Dorman units.
