Tundra 4.7 with P0138 codes [Archive] - Toyota Tundra Forums : Tundra Solutions Forum

: Tundra 4.7 with P0138 codes



MightyThor
07-05-2012, 02:34 PM
My Tundra, bought it with 50,000 miles, has a check engine light on. I found out that it had 2 codes, P0138 on both rear O2 sensors. I bought and replaced both O2 sensors my self. Had the codes cleared and after 20 miles the engine light is back on showing the exact same codes. High voltage on the rear O2 sensors on both sides.

What else could be causing this? Anyone have any idea why a truck with 70000 miles would be displaying this with new sensors installed?

Thanks in advance for any information that is shared.

Oh one other issue that the experts might know about. I noticed that both back wheels have some oil inside the rim. A small amout. I removed the back wheel and found that there is a very small hole on both sides that this oil is coming from. The hole is there from the manufacturor but I am not sure what it is. It doesn't appear to be brake fluid as the level in the resevoir remains constant. What could this be? Could it be gear oil from the rear end????

MightyThor
07-05-2012, 02:36 PM
I left out some information. The truck is a 2006 Tundra, Full cab. It has a 6" lift kit on it.


thanks again

marvbest
07-05-2012, 02:45 PM
That leak surely sounds like both rear axle seals are leaking. You need to address that issue IMMEDIATELY as your rear brakes will (if not already) soon be coated with differential lube and you'll have NO REAR BRAKES.

nyskg
07-08-2012, 02:06 PM
did you use Denso?

Stone_Blue
07-08-2012, 06:02 PM
Causes for P0138:

HO2 sensor (sensor 2)
Short in HO2 sensor (sensor 2) circuit
ECM internal circuit malfunction

Well, I guess you MIGHT be able to rule out the O2 sensors, since they are new. Like nyskg mentioned, what brand are they? Toyotas are pretty picky about different brands of electrical and sensor parts. There should be a voltage or resistance check for them in the manual.

Next, I would start checking relevant connectors, then you may have to resistance check wiring to see if there is a short or open somewhere.
Unless you happen to have a spare ECM laying around you can swap in?

MightyThor
07-10-2012, 04:37 AM
No i didn't use denso. I used bosch. I get the same error I got with the originals. It is just odd that both of them went bad??? Is there a fuse that could have gone bad somewhere? Both sides are saying "high Voltage".

Spare ECM? Control module?

2003bajatundra4x4ac
07-10-2012, 07:06 AM
take those bosch out and buy denso's. bosch are notorious for giving problems. start fresh and see where you are.

Remmy700P
07-10-2012, 12:42 PM
take those bosch out and buy denso's. bosch are notorious for giving problems. start fresh and see where you are.

+2. ECU-related components are specific in regards to operating voltage ranges, therefore, only Denso sensors are appropriate for your Tundra.

MightyThor
07-11-2012, 06:53 AM
let me ask you this. I will order me some Densos. Do you think that the fact that I have 37" tires installed on the truck may cause the problem? My speedometer is off 10mph. It may sound crazy but all of this started around the time the mods were done? it is just weird that both go at the same time and both give the high voltage nag.

Stone_Blue
07-11-2012, 09:38 AM
If thats the case, after you get the Denso O2 sensors in, I would start checking wiring, and especially any ground points, under the truck. Something may have gotten pinched or broken, or a loose connector while doing the other mods.

Remmy700P
07-11-2012, 09:42 AM
let me ask you this. I will order me some Densos. Do you think that the fact that I have 37" tires installed on the truck may cause the problem? My speedometer is off 10mph. It may sound crazy but all of this started around the time the mods were done? it is just weird that both go at the same time and both give the high voltage nag.

No, that's a gearing issue, not a fuel-air trim problem.

I'm with Stone_Blue. I'd be closely inspecting for pinched/sliced/abraded wiring.

MightyThor
07-11-2012, 01:30 PM
Any chances of getting hold of a print? I would like to trace it out. It has to be somewhere where both harness' meet. It seems that if the circuit has a heater built in, it should have a fuse. i don't know. But if there was a schematic/ print or something to look at. I feel I could trace it out.

marvbest
07-11-2012, 02:15 PM
Free .PDF copies of Tundra Factory Service Manuals (FSMs) are available from Toyota Tacoma/ 4Runner/ Tundra/ FJ Cruiser Factory Service Manual Page (http://www.ncttora.com/fsm/index.html)
Just go to that site & select the year(s) you want and download. Electrical schematic drawings are included in the FSM.

2003bajatundra4x4ac
07-11-2012, 02:28 PM
Free .PDF copies of Tundra Factory Service Manuals (FSMs) are available from Toyota Tacoma/ 4Runner/ Tundra/ FJ Cruiser Factory Service Manual Page (http://www.ncttora.com/fsm/index.html)
Just go to that site & select the year(s) you want and download. Electrical schematic drawings are included in the FSM.

isn't the internet awesome?

MightyThor
07-12-2012, 09:17 AM
Of course it is awesome. But the helpful members of this site make it even better.

MightyThor
07-12-2012, 09:52 AM
Well I have determined a couple of things with this.

1. I am an idiot
2. I am too old for this

I went to those sites and down loaded all those files. I can not find any wiring details for the 02 sensors. There are sooooo many abbreviations and acronyms that it may be impossible. With the o2 sensors being heated, you would think that it would not be hard to find the diagram.

Is there some technical name for these circuits that I don't know about?

marvbest
07-12-2012, 10:04 AM
What year 4.7L do you have? Also, what cab type as that does also make some differences in electrical wiring configurations?

MightyThor
07-12-2012, 12:06 PM
It is a 2006 double cab 4x4 4.7 engine. It has a 9 inch lift kit and 37" tires. The check engine light will not go off. Display shows P0138 codes.

Remmy700P
07-12-2012, 04:25 PM
The "circuit" we are referring to is the oxygen (O2) sensor's heater element circuit. It is internal to the O2 sensor and is used to heat the sensors substrate up to proper operating temperature. It is a separate component to the sensors actual lambda (air differential) sensor.

rjparker
07-13-2012, 05:31 PM
Hopefully someone did not give you the wrong code since there are 4 oxygen sensors, two up by the engine on the exhaust manifold that are hard to get to and usually go first AND then two that are under the seat area also on the exhaust manifold that are relatively easy to see and access.

After clearing codes the O2 sensors will show ok for awhile, changed or not changed. So you may have more to change. I found no issue with aftermarket sensors even the cheapest ones where you install your old connectors to the new sensor. More chance for wiring errors of course.

Second, the oil seals on the back of the Tundra might be expensive. Toyota will want to change the bearings and bearing holders along with inside and outside seals on each side. Maybe even the axle shaft. Your brakes are probably already soaked. Just changing the primary oil seal often does not hold. I know as had it done by a "quality shop" several times (only once at my expense) until they called Toyota and said what gives....

Possible O2 Sensor error causes
- Rear Heated Oxygen Sensor Bank 1 harness is open or shorted
- Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection
- Faulty Rear Heated Oxygen Sensor Bank 1
- Inappropriate fuel pressure
- Faulty fuel injectors
- Intake air leaks may be faulty
- Exhaust gas leaks

Read more: http://engine-codes.com/p0138_toyota.html#ixzz20YLin5oT

thombiz
07-13-2012, 06:39 PM
Ok, I've been there with my '09 5.7. I'm not absolutely sure this is correct, but I'd bet it is, so here goes. On my '09 there are two O2 sensors (downstream) and two air fuel ratio sensors (upstream) I was guided by someone on these forums to replace the O2 sensors as well as the air fuel ratio sensors. See my posts here and check out the thread: http://www.tundrasolutions.com/forums/1gen-tundra/223636-o2-sensor-code-replaced-light-continues-2/#post1795038 Here's the deal.... the air fuel ratio sensors can missread causing the engine to adjust in a way that trips the O2 Sensor malfunction codes. You need to replace the air fuel sensors as well as the O2 sensors at the same time. Note these are side specific. I purchased the Denso exact part numbers for about $365 and it took about 45 minutes to change them out. Problem solved. I think...that is the solution you seek. Be sure to check my post mentioned above and the threat where it was found. I've not had a single check engine light for months now.

Stone_Blue
07-13-2012, 07:39 PM
The testing procedure and circuit is detailed in the Diagnostics->Engine 2UZ-FE section of Vol. 1 of the Repair Manual, and a more detailed circuit diagram showing connectors, junctions and ground points is in the Electrical Wiring Diagram Manual, under System Circuits->Engine Control 2UZ-FE.
The manuals are available in .pdf format (readable by free version of Adobe Acrobat Reader), from this site:

Toyota Tacoma/ 4Runner/ Tundra/ FJ Cruiser Factory Service Manual Page (http://ncttora.com/fsm/index.html) , under 2004-2006 Toyota Tundra FSM 1GR-FE & 2UZ-FE.
Doesnt get much easier than that.

The O2 sensors are basically 2 circuits themselves: one for the heater, and one for the O2 measurement. They basically are wired into the ECU (the computer) on one side of each circuit, and on the other they share a common 12V hotwire and a ground wire with several other sensors and indicator lights. Thats basically it.

So theoretically, there should be only 3 things that will cause a P0138 code:

Bad O2 sensors
Wiring
or a bad ECU (computer)

All are pretty self-explanatory. As far as wiring goes, I would expect the issue would have to between the O2 sensors and the next common sensor or indicator, relay, whatever, that they get their 12V and ground from. If it was further up the wiring, I would imagine you would have more codes or issues presenting themselves. I would start with the wiring and connector right at the sensors themselves, and work your way back along the harness. Pull the connectors apart, and really inspect inside them for corrosion, broken pins, or the hardest to identify, LOOSE pins. See if any of the wires are loose or pull out of the back of the connectors. That seems to be an issue that stumps a lot of people on mystery wiring issues.
Identify what other items share the common 12V/ground wires, and check the connectors on those also.
Check for burnt, or brittle sections along the harness. Sometimes a section of harness will touch the exhaust, or be close enough, that the thinner wires and insulation inside the outer wrap will melt and short or break, before the outer wrap burns off, making it hard to locate/identify the trouble spot.

EDIT:
OK, I just checked the FSM myself, and this is the condition that will throw a P0138 code:
"When the target air−fuel ratio is lean and the voltage output is 0.59 V or more (rich)
during active air−fuel ratio control, the ECM determines that the sensor voltage output is abnormally high,
and sets DTC P0138 or P0158."
I could be wrong, but I think this basically says the actual air-fuel ratio you want is actually leaner than it should be, but that the O2 sensor is telling the ECU that it thinks its richer than it should be.
Also, there are other codes that would indicate an open/short in the wiring, so you MIGHT be lucky and not have an issue with the wiring. (I would still check the connectors, and the harness near the O2 sensors.)

The diagnostics section also shows the MAF and EFI relay as related. Have you cleaned or at least inspected the MAF recently? I would try that, thats quick & easy.
The EFI relay should be pretty cheap to swap out.
Did you ever swap the O2 sensors with Denso's?

Edit #2:
The circuit diagram shows there is a fuse for the circuit, labeled "A/F HTR", and another relay labeled "A/F HTR Relay", located in the relay box in the engine compartment, along with the EFI relay. (In the circuit diagrams, the O2 sensors are called "A/F Sensor" (Air-Fuel).

I would be interested to see if its the MAF, EFI relay, A/F relay, or A/F fuse that is the issue. The FSMs sometimes contradict, or more so, leave out things in different sections that talk about the same thing. With this and lots of grammatical, syntax and contextual errors in the manuals, I gotta wonder if Toyota is still having these things translated from Japanese into English, even though the vehicles are at least partially designed, and pretty much totally assembled here in the US.

Stone_Blue
07-13-2012, 08:20 PM
Huh....If thombiz is correct about the difference between the A/F sensors, and the O2 sensors, that is exactly what I am talking about as far as the issues in the FSM. Although there is a quick mention of A/F sensors, just about the whole diagnostics section for P0138 talks about the HO2 (heated oxygen sensors).

I've always heard others on this forum talk about FOUR O2 sensors, two up front, two in back. If the two in front are indeed A/F sensors, NOT the same as the O2 sensors in the back, then I'm glad I learned there IS a difference.

So this brings me to another question then: What is the difference between Bank 1 and Bank 2, and Sensor 1 and Sensor 2?
I assume the banks would be the header on either side of the motor, and the sensor 1/2 would be the front or rear sensor on each side.

P0138 is listed as "DTC P0138 Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 2)" in the FSM.

Remmy700P
07-14-2012, 01:04 AM
Stone, you're making it too difficult.

Bank 1 = Driver's Side
Bank 2 = Passenger's Side

Sensor 1 = Fuel-Air Trim Sensor
Sensor 2 = O2/Catalyst Efficiency Sensor

The 2UZFE has 2 upstream and 2 downstream units.

They are both lambda probes that use internal (exhaust stream) vs external (ambient) oxygen measurements.

The Tundra uses 4-wire heated oxygen sensors. They have an expected life of approximately 100,000 miles. For the price of a new component, the whole measuring voltage exercize is a waste of time.

billsworld
07-14-2012, 07:43 AM
Just because you get a code for an O2 sensor doesn't mean that the sensor is bad. A lot of people think that the code tells you what's wrong, but it is just telling you that it sees something that are not within the programmed parameters. The sensor measures oxygen in the exhaust stream. There could be something wrong in the fuel trim that could be caused by a mechanical issue, i.e. vacuum leak, injector failure, restricted intake, etc. More troubleshooting is required. You also may have a restricted exhaust.

GM
07-14-2012, 10:44 AM
Yeah, FWIW, every time I've had my 2000 Tundra V6 check engine light come on, cleaning the MAF sensor solved the problem no matter what the code, so finally got in the habit of cleaning it before and after the big pollen season with no light in a couple of years now.

GM

Remmy700P
07-14-2012, 12:31 PM
Just because you get a code for an O2 sensor doesn't mean that the sensor is bad. A lot of people think that the code tells you what's wrong, but it is just telling you that it sees something that are not within the programmed parameters. The sensor measures oxygen in the exhaust stream. There could be something wrong in the fuel trim that could be caused by a mechanical issue, i.e. vacuum leak, injector failure, restricted intake, etc. More troubleshooting is required. You also may have a restricted exhaust.

Your argument holds water... IF the code is for operating voltages out of range; posted advice presupposes that the other engine management components (throttle body, MAF, position sensors, filters etc) are in clean working condition. However, 99 times out of 100, when they throw the code for a failed heater circuit, it's the component itself.

lucam
07-14-2012, 07:28 PM
P0138 -o2 high voltage. sounds like broken wire or disconected sensor. check the harness going to that sensor make sure it hasnt rubbed through any where. open the conectors make sure there is zero corrosion.

bnjami
07-15-2012, 07:56 AM
My Tundra, bought it with 50,000 miles, has a check engine light on. I found out that it had 2 codes, P0138 on both rear O2 sensors. I bought and replaced both O2 sensors my self. Had the codes cleared and after 20 miles the engine light is back on showing the exact same codes. High voltage on the rear O2 sensors on both sides.

What else could be causing this? Anyone have any idea why a truck with 70000 miles would be displaying this with new sensors installed?

Thanks in advance for any information that is shared.

Oh one other issue that the experts might know about. I noticed that both back wheels have some oil inside the rim. A small amout. I removed the back wheel and found that there is a very small hole on both sides that this oil is coming from. The hole is there from the manufacturor but I am not sure what it is. It doesn't appear to be brake fluid as the level in the resevoir remains constant. What could this be? Could it be gear oil from the rear end????

I have 2001 Tundra 4.6L and had the same problem with replacing the exhaust Oxygen sensors. Over a period of 8 years I had replaced 5 or 6 sensors. I had always ran high test gas and someone said to try regular unleaded gas. This was the solution for my truck. Several years have past and no problems with the sensor. Try it because it worked for me.

doo/doo
07-15-2012, 11:07 PM
In regards to the oil leak I hope the fix is as simple as mine was. The breather cap on the differential was plugged. I cleaned the vent and used brake clean on the oil soaked parts and so far so good. { 1 year}

MightyThor
07-16-2012, 10:42 AM
All this is great information and I am thankful. I work in quality and am use to making meausurements and tracing wiring etc. I climbed under the truck and started to trace wiring this weekend. As some one stated above, the red wire is shared by several different items. If there was wiring issues there, I would be getting other codes.

The thing that sticks in my head is that both sensors started throwing the codes at exactly the same time. What are the chances of both sensors failing at the exact moment. If one were to go bad I could see an issue with the sensor. Also both sensors share the red wire so that made me take the harness sheathing off and look at the wiring. I did not find any kind of issue at all. This truck is very Pampered and there has been no ruff handling. All the underneath componets are routed and look like they came from the factory.

I could not find any exhaust system leaks.
Harness not damaged, connectors and spade terminals are lubed with dielectric grease
Replaced both rear 02 sensors- still get P0138 code. ( I have a had set that I bought that can read and clear codes).
Inappropriate fuel pressure (This is interesting.) Gonna have to research this more
Faulty fuel injectors (This would only cause a P0138 code) I would think there would be all kinds of problems here. Truck runs and purrs like a kitten.

Stone Blue I think that you are on to something. Once again I am an idiot and am not sure what MAF refers to?? I will order some Densos soon and replace the Bosch. (My son is playing all stars and my time has been limited lately). I will get a new EFI relay also.

Im going to go through that relay box tonight if possible. What you have pointed out makes a lot more sense than (2) 100,000 mile sensors going out at the exact same time under 50,000 miles.
Thank so much and I will keep everyone updated.

speedysaenz
07-17-2012, 01:00 PM
I had the same problem, the good thing is your exhuast is still under waranty, they replaced all of my cats coming to a whoping $2200 but it was covered under waranty due to the 100000 mile exhaust warranty. Just had this done to my 5.7 crewmax 4x4 with 67k 3 months ago!!.
Hope this helps,
Eddie

MightyThor
07-24-2012, 06:31 AM
I have been out of time with my son's little league baseball. I will get back to that tundra!

MightyThor
07-30-2012, 01:29 PM
Well, I am back on the job and started tracing wiring again. Again, I can't find anything. I removed the MAF sensor and cleaned it, no change. So I pulled the manual and started looking at fuses in the engine compartment. I noticed that there are 2 different fuses for A/F, however I can only find one fuse. I am not sure if the second fuse is located in a different area? I am not sure if the A/F fuses can have anything to do with it at all. A/f, if I am not mistaken is air fuel?
I am going to have to order the denso sensors although I feel that it won't make a difference.

MightyThor
07-31-2012, 06:11 AM
There was a suggestion that the issue may be caused or removed by changing fuels. I have always put regular unleaded in my truck so I decided that I would try high test. The change did not make the codes go away. In fact, it made it worse.

i have a reader/eraser that reads codes and can erase them. Before I changed fuels, I could erase the code and drive 100 miles before the check engine light would come back on. When I changed to high test, it takes less than 5 miles before it throws the first p0138 nag.

so changing fuels did not fix the problem, however it made it worse. Any suggestions as to what my next step should be?