Not your average p0157. Please help.

Hey y'all,
New here, first post, hoping I can find some help here. I did search the threads but couldn't find anything that has resolved this.
Just got a new to me turd, 2005 4.0 dbl cab 4x4(with RR diff lock!). 180xxx on the dash, 100xxx on the engine. It's definitely been through the paces, long traveled in the front, blown out suspension in the back. Needs an alignment badly. Salvaged, judging by the core support, front end collision that wasn't all that well repaired(have a new one on the way that I'm going to tack in). Was told the engine swap was "done by a friend" so I'm sure some of my issues may lie there. Found that the battery was only grounded to the body, engine harness was tucked under the battery. Amazed it even started and drove home(fixed that) But other than that, it runs great, plenty of power. I couldn't resist for 8500 bucks. So that's the back story.

It had the b2s2 low voltage code when I got it, that I could see with my cheapo scanner, dude said it randomly popped up one day. My thinking is I know yotas throw em every now and then out of the blue. But when I checked it at home with my good scanner, lots more (srs squib, clock spring, steering angle and some abs stuff) although some of that could be by product from the p0157. That's the one I need to tackle first and foremost so I don't have to worry about smog when registering.

First thing I did was the obvious replace O2 sensor(denso), though I didn't realize bank 2 was driver side initially. So I moved over to there, O2 sensor was barely threaded into the bung. I was too optimistic when I saw that. Put in a new sensor anyway, scanner is showing 0 voltage, while bank 1 is doing fine. B2S1 is doing just fine as well. I checked the af fuse and relay, both good. Swapped the sensor from b1 to b2(again), still nothing. Checked the harness with a multimeter and it was getting 12.xx volts, as was bank 1, so there's power going to it. The harness itself looks to be okay before it tucks up above the transmission, I couldnt see any bare wires grounding out. I chopped the harness pigtail anyway, and jimmy rigged some contacts directly to the o2s coresponding pins, still 0 voltage. I'm suspecting signal wire(I'm not entirely sure that's even a thing? 2 heaters, power and ground right?), but I can't see any damage to the wires past the cat where it meets the main loom. I've cleared the codes multiple times and they pop right back up. Does anyone know how to test the signal? Or where the harness ends up at the ecu? Possible that the connection at the ecu isn't solid? I'm hoping I can find the starting point and run some wires down to the O2 sensor to see if anything changes, but I have no idea where the harness goes once it meets the main loom, and I'm not ready to pull the transmission to follow it if I don't have to. Is there any possibility of this being fixable without me having to tear it down? Lol

I've attached the live data from when I was driving around, going over bumps and everything, it didn't move at all. So it's not intermittent. As well as the other codes Incase anyone knows how to fix that as well lol.

Sorry in advance for the long windedness. Just wanted to be thorough and make sure I gave enough info. Appreciate any advice, and looking forward to being here.

 

More than likely an open or shorted sense wire or open Sensor Ground wire.

Pins on the sensor connector are as follows:

Pin 1 (Blue): Heater Control (PWM Ground from PCM (E5 Pin 5))
Pin 2 (Blue/White): Heater Power (Battery Voltage with key on)
Pin 3 (Black): Sense Circuit to PCM (E5 Pin 33) (0-1v depending on sensor output)
Pin 4 (Brown): Sensor Ground (Ground at all times)

 

I'm sketched out on the whole thing tbh. I was considering an ecm issue only because I believe the ecm was swapped along with the engine. The obd scanner reads a different vin than the frame.

I'm leaning more towards the open wire as well, it makes the most sense, and the engine surprisingly doesn't run rough at all or anything that I can tell in the 2 days I've had it. I've never been good with reading wiring diagrams, but can handle basic wiring just fine, so it's a little overwhelming, but I'm hoping I can manage haha. That pin out of the ecm you posted is a huge help, thank you!

Finding that open wire is going to be a pain, since I can't see any damage in any of the exposed areas, I did see some exposed wire poking out of the sense wire?(thick black one) on the harness and initially thought that was it, but after looking into it I believe that's an interference shield or something along those lines, its like that on bank 1 as well. I'd imagine the open wire would have to be higher up in the loom where it's not accessible . But, in theory, do you think it would be possible to tap the harness at the ecm pinout with jumpers, and do the O2 sensor blowtorch test to see if it reads any voltage? Even just typing that out it sounds like a horrible idea.

 

Definitely could be possible if it's the wrong PCM but let's rule out other things before condemning it.

When an engine has been swapped (especially by someone not knowing what they are doing) anything is possible, wires get tugged and pinched, sometimes harnesses are swapped and aren't the same so things aren't always apparent.

You are correct that the Sense wire is shielded.

Honestly the first thing I would do since we can assume the sensor is good is get a test light connected to battery positive and touch the sense wire at the PCM while watching scan data, if your voltage goes up on scan data the PCM is fine and the circuit has to be open either on the sense wire or sensor ground wire. If the test light lights then the sense wire is shorted to ground, if nothing happens it may be the wrong PCM.

 

This is the last suspect on my list. I was thinking pcms are tied to the engines they came with right, kinda like a motherboard to an operating system? I was hoping the different vin was just a symptom of the pcm being transferred over a long with it's engine from the other vehicle, and nothing more. But that's just me guessing, not entirely sure that's a thing. I'm hoping thats all it is lol.
Either way, I'm not worrying about that till I've tried everything else.

This is exactly what I think happened.

Okay perfect, this is just what I was looking for, thank you so much. I'll run out and pick up a test light tomorrow and test it out. So with that, I would be connecting the alligator clip to the positive terminal, and the probe to E5-33 correct? Again thank you so much, you've been a huge help in my understanding of this.

 

No the PCM should stay with the vehicle, it isn't hard coded to the engine. It doesn't know the difference if an engine is swapped, it's programmed to run a specific type of engine but as long as the engine is replaced with the same type it could care less.

Typically with an engine replacement you want to keep all the original wiring, sensors, and PCM and just swap the basic engine because manufacturers sometimes change subtle things in wiring (even though the engine is the same) between years and even from vehicle to vehicle which can result in a real headache if harnesses are swapped.

Yes.

 

Aw shit okay. So more than likely if my obd is reading a different vin than the frame, I've got a different pcm as well. But I mean as long as it works it should be fine right?

Perfect, will update tomorrow. Thanks!

 

Okay, so. I wanna say I did this right, but I'm not sure. Got the test light, turned the ignition to on, had the live stream going, tested at e5-33, no light, no voltage jump. Went under the vehicle and tested at the b2s2 pins, sense wire, no light, no voltage jump, tested ground, lit up. But while I was fumbling around down there, I did touch the sense wire shield on accident, and it lit up, and then blew the light bulb. Is that shield supposed to be grounded? I thought it was supposed to just be a sheath to eliminate interference. Genuinely confused now, and not sure if I messed something up by touching voltage to it. Gotta source a new bulb for the test light now to -_-

 

Interesting, so it may have the incorrect PCM in it. Get the part number off the PCM and see if it matches what belongs in the truck.
See if the engine code matches the VIN (I believe 5th digit on Toyotas), 2.7L is X and 4.0L is U.

Yes the shield wire on the O2 sense wire is supposed to be grounded, not sure why it blew your test light bulb though.

 

I'm gonna be honest, not sure how to match that up. The frame does have a 5th digit U for the vin, the engine is stamped with a 1GR followed by the serial number, and the pcm is an 89661-04A31, which when searching, pops up as a 2005 4.0L Tacoma, and when I check the vin on the pcm through the scanner, it has a 5th digit U as well, although the vin is not the same as the frame, the first 5 digits are.

 

Okay update, the original test light I had was dogshit I guess. I went and got another one, a better one, has jumpers for both +&-, hooked em up to the battery, and testing the pin again, and this time the voltage jumped and held for the time that I was contacting the pin. So it's safe to safe the pcm is okay right? That would mean that the fault has to be somewhere along the sense wire going down to the sensor?

 

Looks that way, I'm assuming no change when you do the same test at the sensor end?

 

Nada. So at the sensor end, brown shows ground, Blue/white has power, blue does nothing, but as a control wire it shouldn't give off +/- right? Sense wire(black) sends no voltage to the data stream, but the shield wire lights up ground.

 

The sense wire should be black.

 

Correct, at the pigtail it has the sheild. I'm currently following the black wire from E5-33 up through the dash and firewall to see if I can find a break. There is so. Much. Tape. This harness has been spliced to hell, wouldn't be surprised if it's causing some of my other codes as well.

I'm hoping it's up by the firewall where I can access it, and not back down where it drops behind the engine.

Will keep this updated. Thank you again dude, I really can't stress enough how much you've helped me.

 

Think I'm making progress.

Question, does the sense wire shield for bank 2 and bank 1 share a common ground? I found this and it's mangled to bits, but the E5-33 tucks into the sheath, and the shield wire is poorly tapped to a brown wire which I assume is ground, there's also a sheathed and shielded white wire going to a different pinout, which I can only assume is the bank 1 sense wire. And they were taped together, but not connected very well, if at all.



This shit is honestly such a mess, there's also a purple wire coming from E5-8 that's been cut and left off, and another purple wire coming from another module. From the pinout if I read it right it's the park/neutral position switch? Weird cause the truck shifts just fine and at least obd side knows when it's in park.

 

Either I wiggled something back together, or I found the issue, cause as far as can tell, the wiring in the loom under the dash and by the fire wall for E5-33 and it's sheath look in tact aside from the mangled shield wire. I've left the white sensor wire shield detached from that ground bundle, plugged the pcm back in, and tested at the pigtail, and wouldn't you know it, we have voltage!

So now my next question is, did I just jostle something back together, or was that common ground causing interference in b2s2 signal wire?

 

Srry for the delay, got busy.
Yes the shield wires and sensor grounds all share a common ground, the shield wires splice together in the harness and the individual ground wires are tied together at the J12 Junction Connector which gets it's ground from Ground Point EE on the back of the Right Cylinder Head.

Not sure why they would have done that, if the other module your referring to the box next to the PCM that is the Junction Box No 2 (essentially it ties a bunch of circuits together internally). The wire your referring to I bet goes between connector PA Pin 11 and E5 Pin 8.

I bet you moved it just right that either a broken wire or poor repair made connection, if the shield wire was shorting it out I would have expected that to show up with the test light test I had you do.

 

Nah no worries! I was trying to make sense of the wiring diagram and figured the sheilds share the same ground from this

Me neither, but nothing surprises me at this point. I did trace that other loose end back into the junction and I believe it paired up with yellow/black. So I taped the ends together. Nothing blew up so I'm guessing that's right.

Yeaa..that's where I'm at right now. When I had it it all pulled apart, tested the pigtail, and sensed the pcm sensed power, with obx1 sheild disconnected, and obx2 just kinda hanging there with what little connection to the shield it had. I went over the diagram to be sure, grounded both shields back to their shared ground. After I did that, both sensors on live data were showing .015v baseline, and that was with obx2 disconnected. I wasn't sure if this was normal, as some stuff I'd looked up said all the sensors will have a very low nominal voltage.


I wasn't sure if this was a baseline or not. But I went ahead and plugged obx2 sensor back into the pigtail, and drove around. The result was obx1 functioned normally, whole obx2 stayed at .015, obx2 is no longer sen

Odd thing is, if I shut the truck all the way off, and turn ignition back to on, both sensors start at 0. But when I give either one any voltage, they baseline at .015. But obx2 is no longer sensing power again. So, I agree with you, there's gotta be something loose. Odd thing is, I only ever went under the dash and just past the fire wall, where I could access. I can't see any visible wear or damage to the obx2 sensor wire aside from that messy shield wire. The sheath past the firewall is in tact as far as I can tell, but I haven't pulled the loom out of the boot behind the engine yet. I'll have to continue that tomorrow. But I've figured out how to rig the probe to stay in the pigtail, so hopefully I can wiggle some shit around and watch the live data for a spike.

 

No the violet wire should go straight from the PCM (E5 Pin 8) to PA Pin 11, The only Yellow/Black wires at connector PA are the L4 Detection Switch Signals.

I can't remember if Toyota uses a bias voltage or not (I don't believe they do), that seems about right for open circuit voltage.

They will, an O2 Sensor doesn't function until it reaches a certain temp which is aided by the heater. Toyota delays turning the heaters on on the downstream sensors until certain parameters are met so the sensors will read 0 until the heaters turn on and bring the sensors up to temp.

I suspect something got pinched or pulled apart when it was wrecked or when the engine was installed, maybe it was "repaired" sloppily (but you should see non-factory tape) or maybe it never was.