Need help with code p1135

So of course my truck throws a code right when I get the smog notice in, and I need some help figuring it out. I've been trying for the past 3 months to fix it but I'm having no luck.

She's a 2001, 3.4 DC 4x4.

What I've tried so far:

1. Bought a sensor off of Amazon (

$145 Denso 234-9001 Upstream Air Fuel Ratio Oxygen Sensor with 10.6” 4-Wire Harness, for Auto Trans Equipped Vehicles

Denso 234-9001 ), installed it and cleared the code. Didn't work, light came back

2. Cleaned the MAF sensor with crc cleaner, didn't work

3. Bought a new MAF sensor ( Denso 197- 6020), installed it, cleared the code . Didn't work

4. Cleaned the Throttle Body and IAC with crc tb cleaner and installed new gaskets, code cleared, didn't work

5. Checked the efi relay by jumping it , relay works fine

6. Checked the 20A fuse, fuse is fine.

7. Checked continuity between the relay and fuse, its fine

8. Check the continuity between the relay and the plug to the sensor, It's fine

9. Checked the continuity from the sensor plug leading to the ecu, they're fine

10. I cleaned everything with crc electronics cleaner, checked all the connections. Didn't work


At this point I gave up and took it to my mechanic. He called me the next day saying he has no idea what it is and his best guess is that it's something wrong with the ecu. When I dropped it off I gave him the old sensor, and he said he tested bother the old one and the new one, and they're both within spec of the resistances. he said he tested the voltages to the sensor and it was fine, he even took it out and felt it heat up perfectly . He said take it to the dealer and keep him updated.

11. I decide to tackle it again. And test the voltages for myself

Voltages with the truck running:
HTAF : 13.86 measured at the ecu plug
AF1+ : 4.05 measured at the ecu plug
AF1- : 3.75 measured at the ecu plug

The manual that I found says specs for AF1+ is 3.3v and AF1- is 3.0v

My readings are higher but still .3v difference.

12. Bought the rear O2 sensor (

$61 denso 234-4189 oxygen sensor

denso 234-4189 ) and plugged it in without installing it because the current one is rusted as fuck. Knowing this would probably set off other codes , I hoped it would at least get rid of the p1135 if it was some sort of short. It did set off other codes but did not get rid of the p1135. I now have an extra b1s2 sensor

13. Took it to the dealer and they say that the sensor is bad. They said that it's slow to respond and giving off the wrong waveform ( maybe the .3v difference in voltage I'm getting?) . They recommend I buy an oem sensor. The sensor cost $330 and $550 with install. They said that they've seen aftermarket sensors do this from time to time. I asked the service writer how sure they were and she said she had two other techs look at it before calling me to confirm. I asked if there's anything else they thought it could be and she said that they're pretty sure it's the sensor. I told her I'd need a few days to think about letting them replace the sensor. She even called back after I left and told me about the drive cycle if I decided to do it myself, which I thought was cool of her.

14. I chat with Amazon to refund the sensor and they say that it'll be a $16 restocking fee. Ask them why this item will be restocked since it's broken ? They then offer a replacement for free and if the second doesn't work they will refund me full price.

15. They send me a new sensor and I install it and clear the code. The damn light still come back on.


So this is where I'm looking for advice.

I'm hoping for any other tests / checks / ideas anyone knows of or if there's maybe something that I'm missing that is super obvious ( Or even not ).

What are the chances that amazon sold me two bad sensors?

Do I buy the $330 sensor? I thought this thing is also made by denso, so why would it be any different ? Also if I buy it from the dealer I bet they won't refund it if it didn't fix it , even if they said that was the problem...


Should I try a new ecu ? I found a company online that will code the vin number before they ship it so it's pretty much plug and play.


Should I go the dealer route and let them Install it ? That way if it's not the sensor that they said it would be , they'd cover the cost of the repair... I hope.

There is one good thing that has come out of this though , all that cleaning and part changing got me from 12 to 15 mpg on average.

Sorry this post was so long, thanks in advance.

 

P1135 is a problem with the heater circuit in the Bank 1 Air/Fuel ratio sensor, it has nothing to do with the MAF sensor or downstream oxygen sensor.

 

Not sure about your part number either, Rock Auto shows 2 different part numbers looks like it depends on transmission and whether or not it's California emissions.
https://www.rockauto.com/en/catalog...43,exhaust+&+emission,oxygen+(o2)+sensor,5132

 

Correct, but they are on the same circuit coming from the efi relay. The only reason I cleaned or checked those was to make sure one of them wasn't causing a short. I have changed the bank 1 sensor 1 twice with the correct part from denso. I only checked those other items after changing the sensor did not work.

9001 is for the auto , this is what I used twice.
9003 is for manual, I did not use this one.

 

Did you ohm check the heater circuit on the original sensor to see if it was indeed bad?
There's been many reports of people getting counterfeit parts from Amazon and Ebay so I suppose it's possible to get 2 bad parts.

 

Also did you check All powers and grounds at the PCM?

 

Yes. Both the one that was on the truck for as long as I've had it and both the new ones were all within spec.

Yes, The voltage readings I got were done by getting a reading from the back of the connector at the ecu while the engine was running.

If you are asking if I checked every pin on the ecu, then no, I did not. I only checked voltages on the ones that are related to the bank 1 sensor 1 circuit.

 

I don't mean all pins but I would check all the powers and grounds to the PCM, it could by an off chance be a bad ground at the PCM.

 

I like this idea, I'll try to find out where all the grounds are and give them a cleaning. Thanks.

 

Denso makes sensors for Toyota, I just got the rear O2 myself for ~$65 through a Toyota dealer on fleabay

the A/F shouldn't be more than ~$120 ish I think. Can also check the online stores or do a search for the part number and you will most likely get a plethora of options to buy straight from dealers

 

I only paid like 120 on Amazon for the front denso sensor. I did search around online for the toyota oem sensor and I found them for like $180 -220 which is cheaper than the one my dealer wants to sell me. My concern is that if the issue isn't the sensor and I buy it from a different dealer there will be no returning it. At least my dealer might take it back since they were the ones that said it was the sensor that is causing the issue.

 

https://www.tacomaworld.com/threads/spot-the-fake.632516/
Pix of Toyota

$145 234-9001 Upstream Air Fuel Ratio Oxygen Sensor with 10.6” 4-Wire Harness, for Auto Trans Equipped Vehicles

234-9001
Take a close look at the laser etched DENSO ID

 

Do these continuity tests again while twisting and flexing the harness, might have a shitty spot in a wire that intermittently goes open circuit.

 

This is the one i got from Amazon. Both of them look similar. The one in your post seems to use a different font, especially the bottom numbers? think mine are fake?

I will try this, thank you. It also gives me another idea. I might try to bypass the wiring harness altogether and connect the HTAF AF1+ and AF1- to the ecu with my own wires to rule out the harness.

 

It's legit
Fakes don't get laser etched

 

P1135 code was NOT the A/F sensor!

I'm posting this in case anyone else finds themselves in my position.

Check engine light was on. Got a p1135 code. Thought this would be an easy fix. I replaced, myself, the Bank 1 sensor 1 (upstream) sensor with a brand new Toyota sensor. Still got p1135 code. [I tested my old sensor and the 2 black wires had a 1.1 ohm read, which is OK - I had a feeling it was not the sensor].

Took my truck (2001 Tacoma 4WD V6, manual) to my local dealer and paid $50 for a troubleshoot. I told them the sensor was brand new. After their troubleshoot they told me it was a bad sensor. [I had a feeling they were wrong].

I replaced the sensor again, part under warranty - still got the p1135 code.

Visit #2 to the dealer. This time they put the shop foreman on the job (very experienced guy they said ). The problem was a ground wire attached to the intake manifold. Problem fixed, no CEL light for a week. No additional charge from the dealer. Total cost to me was $50.

I attached the invoice so you can see the troubleshooting steps taken by the mechanic.

Hope this helps someone in the future. This forum has sure helped me.

 

Did they happen to show you where the location was for the ground wire on the manifold?

 

On the 3.4 the ground wire bundle is on the upper intake manifold drivers side. Usually brown or brown/black wires.

On a side note, checking the ground by resistance test only is misleading, a small side marker bulb (194) and socket will put a small load on the ground side. If the ground is questionable, the bulb will barely glow. A test light does not have enough electrical load to preform this test. The big concern here is how many amps of ground load can the circuit take as it is the PCM that provides the ground path.

 

I have the same exact make model and year tacoma as you and 3 days after purchasing my tacoma in November of 2023 my CEL light came one my dash. My gas cap broke off that little olastic connector piece and the rubber ring around the gas tank where the gas pump nozzle goes is like off center additionally but I don't think that is the issue as I've ran and cleared the code a few times just so see if same code is displayed and it repeatedly has showed the p1135 code as being the cause for my check engine light illuminating. My truck was reported to have failed inspection for frame rot in as early as 2004. And was already part of the frame recall. Have you had the same problem with your truck and the frame and what measures have you taken to repair and prevent corrosion if so?