Getting these two codes and they're driving me nuts. Heater circuit malfunction. From what I can understand, p0135 is the front sensor, p0141 is the rear.

This is a 1997 4runner 3.4, manual, 4x4 ECM with one cat. Upstream o2 and one downstream.

This is a 3.4 swap. Donor vehicle was a 1997 4runner going into a 1986 Runner. I've done a few of these swaps without any issues for years now so I'm fairly confident that I know what I'm doing. Wiring is clean and not a hack job but that's not to say that something couldn't be wrong.......well because there is something wrong obviously.

When the vehicle fires up, I get the p0135 and p0141 almost immediately looking through laptop connected to the obd2. Within 1 minute every time. Clear the codes via the laptop, thy come right back within a minute.

I went through the fsm and performed every check I could find, which isn't much unless I missed a few things.

Tested the wiring. I get 12v to the white/blue wire, ground to the brown/red, and have continuity between the heater wires and data/sensor wires from both sensors to the ECM and have confirmed multiple times they are going to the correct ECM terminal. Everything looks right.

Checked the sensors themselves, which tested at 13.5 front and 13.7 rear resistance across the heater terminal and the 12v terminal. Seems within spec according the fsm. It was about 90 degrees yesterday here. Motor was cold.

I just cannot believe that both of these sensors went bad sitting here waiting for the swap to occur and the both of them had the heater circuit go defective. They supposedly worked fine before the swap.

I can usually figure stuff out but I'm totally stumped on where to go from here. Wiring appears ok,sensors test ok.

Any ideas?

 

If you are sure the sensors are good .

No major problems in the wiring .

The only thing left is the ECM do you have access to one to test with??

 

Did the sensors get swapped during the process? As in the rear sensor is up front and the upstream sensor is after the cat?

 

Yikes, kinda sounds like bad ECM based on what you're saying. Do let us know.

 

Sensors didn't get changed, already swapped to know good ECM from my truck.....same one.

Completely stuck!

 

Maybe grounds? ECM ground? Can you swap sensors with your other truck? Although I highly doubt both sensors go bad at the same time.

 

My guess as well. Specifically the sensor ground by the diagnostic plug and the battery to chassis ground on the fender.

 

I ran a 4ga. Ground from the battery to block, 8ga. From battery to fender and also the 10ga from the back of the block to the firewall.

Cleaned the connections on the manifold ground and made sure tight.

 

I was never able to get a good ECM ground on the manifold I ended up running it direct to the battery.Despite my best efforts I just could not get the aluminum clean enough using new hardware

Another possible problem is the sensor plugs are corroded things look good with a meter test probe but don`t work when plugged together.

What is bad is your really unable to detect the corrosion with the naked eye.

Good luck

 

Is there anything else that would interact or control this circuit that could cause the heart circuit to fail? By looking at the fsm wiring for the o2 heater circuit, it seem like like is simply one wire for each sensor for the ECM controlling the heater and that's it besides the ignition power from EFI relay and ground.

 

Actually, the heater ground is provided by the ecm. Heater circuit:

EFI 12V+ >> Heater >> ECM >> Ground.

The other two wires go to the sensor only, one ground and one from ECM. The sensor circuit and heater circuit do not interconnect, so the ground at the sensor is not for the heater, just the sensor.

So its just EFI 12V+ and the ECM lead for the heater side. That's it. Heater, ECM or connections, nothing else involved. You could try a new temporary by-pass wire from the ECM terminal to the heater as a test. Then do the same with EFI 12V+ if no joy. Sometimes a wire connection will ohm out good but will fail under full heater current. The heater draws a few amps, the meter is only milliamps.

 

This good to know. Thanks.

 

Reading in other forums about a heater fuse somewhere. I guess if the fuse (if there is one) was bad you wouldn't have gotten 12v at the sensor though.

Genuinely hoping each of your replies will bring resolution...

 

I know there is a heater fuse not on the passenger side of the radio accessible from inside the glove box. I always assumed that was for the acual heater. I don't think that the issue as it's getting power. Who knows though cause I have no other solutions.

 

Back at this after a few days out of town.

Here is what i am getting.

red lead of meter to blue-white wire, ground lead of meter to chassis........12V
this is on both sensors wires.

Red lead to blue-white for each 02 sensor and ground lead to pink wire(heater ground) .4-.6V (front sensor)

Red lead to blue-white for each 02 sensor and ground lead to red-white wire(heater ground) .4-.6V (rear sensor)

This doesnt seem good as shouldnt it be 12v with the meter leads across the blue-white (power) and either of the pink or red-white wires (grounds from ECM)

I noticed that according to the OBD2 program that I using, it is staying in open loop at 192 degrees. Thats not right is it. I always thought that it should go to closed at about 165. I know that there is a code for that (P0125???), but I am not getting it.

Could this be related?

I have no idea where to go from here!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Here are some shots of my readings

 

Well I ended up checking all the connectors, tearing apart the harness, taking the covers off the ECM and checking the junctions right onto the circuit board rather than the pins on the plugs.

Still not 100% sure what the issue was, and that makes me nervous, but it is all working. All monitors have ran and passes. No cel.

I think that the issue was the female pins in the plug were no making good contact with the male pins on the ECM. This was certainly an issue giving me a misfire on #5 that we couldn't figure out after swapping coil packs, plugs, injector, etc.

All seems good now. Just didn't want to let this thread hang and maybe it'll help someone out down the road that's searching. Check those pins and confirm continuity straight to the board of the ECM.

 

Glad you found the problem.

 

Glad you got it sorted!!

 

That's a bit bittersweet; glad it's now working, but without knowing what you did to "fix" it who's to say that it will stay "fixed"

Something to think about, when I had my engine harness out and re-pinning it for M/T ECU connectors I "re-crimped" most all of the metal pins on the ends of the wires, then fast forward 6 months and I kept getting an intermittent TPS fault. Turns out my "re-crimping" caused the pins not to set in the plastic connectors like they should and they had some wiggle room and would occasionally wiggle loose causing problems. A bit of hot-glue (the same stuff from the craft store) to the wires on the backs of the connectors (with engine running to ensure they were in the right spot and making good contact with the ECU) and I've been problem free for a year and a half.

 

Well the codes are back. Very frustrating.

I just can't imagine that BOTH o2 sensors are bad but I guess that is the next step. Really gonna hate buying new sensors and have the same issue.

Just noticed that the part numbers are different for manual and automatic for the upstream sensor. The downstream is the same.

This was an auto motor that was repinned to manual with a manual ECM. Seems intriguing but I've done this twice with the exact same setup (ECM, o2 sensors, etc.) without issues.

Any insight into why there are different sensors for manual vs. auto?