P0138 & P0606 error codes

On this Maundy Thursday, when a lot of people commemorate the passion of Jesus Christ and his upcoming crucifixion, I am being persecuted too, with no fault of mine…because of my car :slight_smile:

Jokes aside…this is the story.

2005 Toyota Corolla
Car was not driven for about 10 days. When started up yesterday, CEL came on and gave like 7-8 error codes - P0138 & P0606 repeated few times. Does this repetition of the same two codes mean that these error codes were getting recorded for a while and CEL waiting to come on?

No loss of power or acceleration. It is a stick shift and I can still gun it. But, I did notice that fuel economy seems to be poor (could also be because of infrequent driving). I usually would have driven over 200 miles when the fuel gets to half tank mark. Now it’s only around 150 or less. Long term fuel trim was +4.6% and short term fuel trim was like -2.6%.
Also, the O2 sensor readings were not doing the high-to-low voltage switching. Does that confirm that the O2 sensor is bad? Will spraying the MAF cleaner on O2 sensor do any good?

What would be a logical way of approaching this issue, from the simplest to the most expensive? Has this combination of codes happen to anyone else? How did you fix it? (I hope changing the pcm is not one of the fixes…i wish it won’t come to that).

It rained heavily yesterday, but the car was not driven through rain. Can this have something do with this issue? I cannot think of anything else that could cause it recently (or, is it something that was going on for a while without lighting up fhe CEL?). I will be cleaning the MAF sensor and air filter today and checking the wiring on the O2 sensors and the wires to fhe pcm.

By the way, few weeks back I did some repairs to the srs module on this car. I cleaned the wiring harness to the pcm too at that time (it had some slight signs of corrosion). I am going to check those too today.

Thank you all, in advance, for your suggestions and advice.


Wow…that is kind of funny… Yesterday a friend asked me to look at her car a 13’ Toyota Corrolla. It had the check engine illuminated as well as the trac control light. So I pulled the codes… In her instance they were P0138 and P0607. The P0607 seemed rather ominous to me the 138 was supposed to be an O2 sensor Bank1 Sensor2 which would be the Aft 02 sensor after the Cat.

Curiosity made me go to a few forums that discuss Toyotas exclusively as I was a bit worried about that 607 and I found out some interesting information. The 607 is a very loose and fuzzy code description and in Toyota’s instance it seemed rather common within the forum. Most of the solutions revolved around looking into ground connection integrity…otherwise the general consencious was “there may be something wrong with the ECM” Not good. SO, I read a good bit about it and found out something somewhat strange. While the 138 points to the second 02 in the system for some reason more than a few guys I trust state that they replaced the 02 the car was telling them to replace HOWEVER… What fixed it was the upstream O2 sensor and not the one the car pointed toward. Everyone I talked to also had the 607 as well.

Not sure why this is to be honest and I really dislike that 607 but the people I talked to gave me that good information about their 607 codes that were also packaged with an o2 sensor code. I am going to run with it.

So my friends 13’ Corrolla will be receiving 2 new O2 sensors in her instance there are enough miles on her vehicle to warrant a replacement at this point. Im ok with doing that because there are no solutions to that 607 that make any sense to me, they are very obtuse, both in problem description as well as resolution of that code.

So if that many people have the same issue on their Toyota’s and they came close to tearing out their collective hair trying to solve it using only one O2 sensor (the one the code pointed to) with a 100% failure rate at curing the 607 problem, I am listening to what they found was the solution. Just some info for ya…use it as you see fit.

The guy at O’Reillys who first pulled the codes first also asked me to check the upstream O2 sensor. The downstream O2 sensor was replaced, maybe an year ago.

By the way, are the upstream and downstream O2 sensors interchangeable on a 2005 Toyota Corolla S?

I have a spare downstream O2 sensor. I was wondering if I could use it to replace the upsteam sensor.

No they are absolutely NOT interchangeable. The upstream sensor is responsible for fuel trim adjustments and is usually more expensive than the downstream. Sometimes by a large amount.

I checked the resistance on the upstream O2 sensor and it is showing somewhere in the 3-4 ohms range. I read somewhere that it is supposed to be in the range of 11-16 ohms. Can anyone confirm this?

Also, there are no obvious signs of frayed wires on the O2 sensor.

So you changed the O2 sensors without finding what caused it to go bad? Usually,an engine that burn oil at an alarming rate will foul them.


Actually, that was a foolish action on my part at that time. Later, when I bench tested the oem O2 sensor, it was perfectly fine. Surprisingly, my spark plugs are clean and oil level is not going down. Won’t the spark plugs foul up if engine is burning oil. I’ll check the color of the exhaust smoke next time I start it up.

As I was trying to see what was making the O2 sensors to go bad, I noticed that the fuel injectors were making some sort of a puttering sound. Actually, I think only one or two were making a loud’er’ sound than the others. Are they supposed to do that? Could that cause a high voltage situation for the O2 sensors?
See video

Also, I tried to create a lean condition by removing a vacuum line on the pcv valve. It made the O2 S1 to go up briefly. Otherwise, it stayed pretty much at around 1 v while the sensor 2 stays at close to 0 v, pretty much the whole time. I don’t see much fluctuations. What do you make of this? Maybe the O2 sensors are out, but this time, I want to fix whatever is causing it too.
Here and here are some screenshots of the obd2 live data taken at 2000 rpm. Shouldn’t the air-to-fuel ratio be 14.7:1. For me, it stayed somewhere closer to 14:1. I cleared the codes to see if it comes back on after it a certain number of cycles.

I checked voltages on all pins on the wiring harness to the sensor 2. There seems to be the 12 v, 0.3v signal, ground and another lower voltage. I think the wiring is ok.
Can a leaky manifold gasket cause all these issues?

I am also tempted to use one of the catalytic cleaner fluids that you add to gas? Will that mess things up more?

Had that exact same scenario this week on a Toyota product. One of the guys replaced a downstream sensor for a P0138 while I was on vacation and the car came back with the same code. I found a failing upstream sensor.

P0138 simply states that the ECM is receiving a voltage signal from the downstream O2 sensor that is out of the expected range for that sensor when it is operating properly. Many times that’s because the upstream sensor (an Air/Fuel Ratio sensor) is getting lazy and causing a shift in fuel trim that hasn’t yet set a fault code. But the catalyst is working harder and it shows in what the downstream is reporting.

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