1996 5 speed intro

[4Reak Show]

A common misconception of modem vehicles is that a scanner tells you want part to replace. Although this MAY be true 99% of the time, technically the code only refers to the CIRCUIT.

P0141 is for the heater control circuit. Basically the ECM completes the circuit, either directly or thru a relay, and watches for amp draw or for the 02 to start changing. 99% of the time it's the 02. Having gone thru 2 on yours with the same result, I'd be edging more towards a circuit issue.

I no longer have access to wiring schematic databases but I'm guessing someone on here does. You need to track down where power and ground come from to feed the 02 HEATER circuit and see where it drops out. It could be something as simple as a pin backed out of a connector somewhere or a small ground wire broke or wasn't put back on after a repair.

Good luck

 

[habanero]

I'll be under my truck on Wednesday afternoon as it's supposed to dry out and warm up a little by then and am still planning on checking- though it sounds like if it's o2 it's on the other side of the plug(s).

 

[onemanarmy]

A common misconception of modem vehicles is that a scanner tells you want part to replace. Although this MAY be true 99% of the time, technically the code only refers to the CIRCUIT.

P0141 is for the heater control circuit. Basically the ECM completes the circuit, either directly or thru a relay, and watches for amp draw or for the 02 to start changing. 99% of the time it's the 02. Having gone thru 2 on yours with the same result, I'd be edging more towards a circuit issue.

I no longer have access to wiring schematic databases but I'm guessing someone on here does. You need to track down where power and ground come from to feed the 02 HEATER circuit and see where it drops out. It could be something as simple as a pin backed out of a connector somewhere or a small ground wire broke or wasn't put back on after a repair.

Good luck

Thanks

Yea...its the wiring or the ECM.

From what I understand, the O2 sensor gets 12V with the key on (maybe through a relay? Gotta check that), then the ECM grounds the circuit.

There has been no work on the vehicle prior to the code showing up (no botched repair or wiring concerns)

I've checked the connection at the computer...it all 'looks' good and clean and unmolested. The connection at the O2 sensor is the same.

 

[habanero]

As you've figured out-
Cold engine last run yesterday afternoon (and 21 degrees out!), key on, no heat.

 

[onemanarmy]

As you've figured out-
Cold engine last run yesterday afternoon (and 21 degrees out!), key on, no heat.

Thanks for that valuable piece of info. I really appreciate it. I signed up for TIS to get wiring diagrams, and in my (quick) scanning of them I believe I saw where the O2 heaters are activated with air flow (engine running, intake air and exhaust gases)...that would explain what we are seeing.

However, the FSM ( that I have) states to do the O2 tests with just the key 'on'

Not clear at all.

I'm about to pull the trigger on getting the ECM checked and repaired if necessary. If that doesn't fix it, i'll have to dig into the wiring harness.

Thanks again.

 

[onemanarmy]

From the TIS downloads:

 

[onemanarmy]

ECU is on its way to get tested/rebuilt. Hopefully that fixes it.

Or more throwing parts at it.

One or the other.

 

[onemanarmy]

So getting the computer 'repaired' did not do the trick. I had it 'repaired' twice.

I'm going to take it to a shop to have them monitor the sensors in real time and properly Ohm the wiring to track down any potential wiring issues.

I did find a 1997 5 speed being parted out, does anyone know if a 1997 and 1996 5 speed ECU are the same? Was thinking about getting the 1997 computer and see if that makes the CEL go off. Just for fun.

Thanks

 

[DaMonkey]

The 97 ecu seems like a longshot if you had yours evaluated, but it would be easy to try if you don't mind that it will prob end up on the shelf.

have you taken a look at cat maybe the cause? i think 0141 looks at sensor response and waits until engine operating temp is up and if it's not responding as expected, it throws 0141 out. potentially it's the cat behavior causing this? can put a laser on front and back of cat to see that cat is actually baking the goods - that's pretty easy. what voltage behavior are you seeing from the sensor readings?

 

[MaineRunna]

Got a favor to ask...

So I've been dealing with a nagging P0141 code (O2 sensors not heating up like the computer wants). I've tested the sensors off the truck, and they heat up in 2 mins with 12V directly supplied. However, I don't know exactly when they are supposed to heat up when on the truck, and to what temp. Do they begin to heat up with just the key on or does the engine have to be running?

So I took both my sensor out but left them attached to the harness and turned the key ON.....neither sensor got warm. I'm wondering if this is normal? I'm trying to narrow down if my ECM is bad.

So, can someone with a 1996 or 1997 3.4l 5 speed run a test for me? Take the sensors out (on a cold engine, hasn't been run in a few days or so) and turn the key on, but don't start it. Let me know if the sensors 1 or both or neither, get warm in less than 5 mins.

I'll paypal you some $ for a 6 pack of your favorite beverage.

Thanks

Just ran out in the driveway and tried it on the front sensor on my 98 which is really a 97. Sensor did not get hot with key on engine off. Rear sensor did not feel hot on the outside either. Check the wiring near the sensor over the transmission.

 

[onemanarmy]

Just ran out in the driveway and tried it on the front sensor on my 98 which is really a 97. Sensor did not get hot with key on engine off. Rear sensor did not feel hot on the outside either. Check the wiring near the sensor over the transmission.

thank you. I *THINK* the conclusion is that both of the sensors don't start to get hot until the engine is running.

 

[onemanarmy]

The 97 ecu seems like a longshot if you had yours evaluated, but it would be easy to try if you don't mind that it will prob end up on the shelf.

have you taken a look at cat maybe the cause? i think 0141 looks at sensor response and waits until engine operating temp is up and if it's not responding as expected, it throws 0141 out. potentially it's the cat behavior causing this? can put a laser on front and back of cat to see that cat is actually baking the goods - that's pretty easy. what voltage behavior are you seeing from the sensor readings?

I have not specifically evaluated the cat, but it runs/drives/sounds/smells normal otherwise. Also, per the FSM, a bad cat is not a cause of this code. The computer opens the heater circuit when the engine is first started to get the O2 sensor 'hot" (How hot? not sure) as to help with sensor output. The code is for the heater circuit not behaving as it should, not an improper reading due to the gasses being off due to a bad/failing/no car converter. Again, per the FSM, it could be the computer, the sensor, or the wiring.

I'm thinking wiring now, but before I start tearing into the interior and wiring harness, the shop says they can see outputs in real time...I don't have the tools to do that. So I'm going to get their take on it.

 

[MaineRunna]

I have not specifically evaluated the cat, but it runs/drives/sounds/smells normal otherwise. Also, per the FSM, a bad cat is not a cause of this code. The computer opens the heater circuit when the engine is first started to get the O2 sensor 'hot" (How hot? not sure) as to help with sensor output. The code is for the heater circuit not behaving as it should, not an improper reading due to the gasses being off due to a bad/failing/no car converter. Again, per the FSM, it could be the computer, the sensor, or the wiring.

I'm thinking wiring now, but before I start tearing into the interior and wiring harness, the shop says they can see outputs in real time...I don't have the tools to do that. So I'm going to get their take on it.

It is the heater circuit causing the codes. Check the wiring near the sensors first, Toyotas don't generally have wiring problems inside the passenger compartment unless it's from mice. It's pretty easy to take the glove box out to get to the ECU to check the engine harness if you have to though.

 

[DaMonkey]

In an off-topic car, I used a test light for this code once and chased the problem pretty quickly.

I tried to find the original article for you that was helpful for me when I learned that trick, and this article just popped up which is an excellent guide. He has smart suggestion to use your old harness for the light. Coincidentally, 3rd gen 4runner was one of the examples he provides and says that the 97 t4r could not use the light because there is voltage to both wires. I'm not familiar with the circuit, but he provides other approaches in the article. Definitely worth a read and just might help you out with where you are now.

 

[onemanarmy]

It is the heater circuit causing the codes. Check the wiring near the sensors first, Toyotas don't generally have wiring problems inside the passenger compartment unless it's from mice. It's pretty easy to take the glove box out to get to the ECU to check the engine harness if you have to though.

Yea, I've had the glove box out and the ECU out a number of times now. Not that hard of a job. All the wiring connections at the ECM look fine.

 

[onemanarmy]

In an off-topic car, I used a test light for this code once and chased the problem pretty quickly.

I tried to find the original article for you that was helpful for me when I learned that trick, and this article just popped up which is an excellent guide. He has smart suggestion to use your old harness for the light. Coincidentally, 3rd gen 4runner was one of the examples he provides and says that the 97 t4r could not use the light because there is voltage to both wires. I'm not familiar with the circuit, but he provides other approaches in the article. Definitely worth a read and just might help you out with where you are now.

Thanks. I've read that article before. It leaves us hanging. What was the remedy for the 4runner? I'm not seeing 12V on both of my heater wires, just one.

Again, i wouldn't think the wirng would be suspect, no work has been done on the car and all wiring at the ECM and at the sensor looks fine. I drove it for about 2 months and then the CEL popped on. Changed the sensor twice (correct denso part, tested with 12V dedicated and it gets hot quickly), had the computer repaired (not sure exactly what the repair was)....so I'm guessing wiring now.

We will see.

 

[onemanarmy]

Got word from the shop, they are saying there is no continuity on the heater/ECM circuit, as some suspected.

I'm going to have them fix it, who knows where the wire break is. They said they could get the CEL off and pass inspection, which is what I need. I hope this settles it.

 

[onemanarmy]

Thanks for all the input on my O2 sensor code. The shop said that both the 12V wire and the ECM sensor wire on the heater circuit were compromised, so they did an overlay and bypassed the broken circuit. They did not dig into the harness to find the broken area so I don't know what caused the cut wires, but the CEL is off now and has passed emissions testing.

Now on to maintenance and mods.

 

[onemanarmy]

CEL is still off and all seems normal.

Just ordered ball joints and bolts from Camelback Toyota.
Ordered timing belt kit from ebay, along with new crank bolt.
Purchased new napa CVs

Gonna be a busy next few weeks.

 

[onemanarmy]

In the middle of replacing both LBJs and going to attempt to reboot the passenger side inner CV.

Used a prybar to hold the hub while loosening the 36mm nut.

The LBJs were a bit worn, but still felt tight. I'm assuming they are original at 226k miles.

Does anyone know (or have) what the thread is on the castle nut that threads on to the steering arm? Mine are crusty and a bit suspect and I'd like to replace them.

Thanks

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