P0606 stumper

Here's the situation:
2005 Tundra SR5, V6, 1GR-FE engine. I've owned it 1 year.

About 2 months ago, I got a P0138 MIL (Bank 1, sensor 2 O2 alarm). Replaced all 4 O2 sensors, just because it was probably time and not labor intensive or financially prohibitive.

Ran fine for about a week, then up pops the MIL again. This time, it's P0606, ECM fault, implying:

1. Power supply circuit short
2. ECM corrupt software
3. Total ECM failure.

My first thought was I got dud O2 sensors and was getting an over-volt from them and the ECM went into fail safe mode. HHS proved otherwise; output voltage within tolerance. Truck runs fine; no starting, gas mileage, or performance issues. Also, the MIL will go out for a few days, then come back on for a few days. When the MIL goes out, the P0606 code goes into pending state.

All that directs me to suspect number 1. But I can't find the circuit that powers the ECM. I have the Toyota Service and Electrical manuals, but after 4-5 hours of reading this, I can't find the circuit that explicitly states which one powers the ECM.

Anyone else run into this and knows a good test to prove or disprove #1? I already know #'s 2 & 3 are going to separate me from significant amounts of cash, so I'm trying to put that off as long as possible.

Thanks in advance.

 

If you didn't use Denso sensors, that probably is your problem. These trucks don't like non-OEM electronics (OEM = Denso, sometimes Aisin brand). If you're thinking "Aww, this guy is one of those dudes! So full of shit!", just LMK, I'll be happy to run through and dig up threads from the last few people who "knew better" but learned otherwise.

If you did use Denso sensors, if you bought from scAmazon or fleaBay, you very well may've gotten knockoffs. It happens. It's happened to me, and other people on here with various auto/appliance/small engine parts. Counterfeiting is rampant these days and nobody seems to care.

Anyway, here's the two things I'll tell you:

• Don't take codes at face value; there are a few red herrings to be found with these trucks. In fact, an aftermarket and/or fake O2 sensor that didn't have the same quality as OEM could easily be backfeeding voltage to the ECM.
• If you want to investigate, check this thread, near the top, about 4, maybe 5 paragraphs in you'll find reference materials like the service manual for '05-'06.

Finally, last bit of advice: Any time you're seeing electrical stuff, check your power and grounds, especially in the engine bay, and at the battery. Why? Check out what I found with my always-southern-driven, 75k mile 2006.

 

PS - maybe a cheap way to tell, although I wouldn't want to run like this for long, would be to, say, unplug the rears only while the P0606 is set, and see if that goes away within 30-40 miles.If so, potentially one of the rear sensors is defective/fake/problematic. Or, just unplug all 4 and see if it goes away. If so, you know one of those sensors is probably backfeeding thru the ECU circuit. I just hate unplugging the upstream sensors because the ECU needs those, technically, to monitor and adjust air/fuel ratio, so the truck may run a little less-than-economical.

 

I took Shifty's advice and got Desno's (234-4209 for downstream sensors). However, I wasn't expecting the sensors to come with no connectors; just bare pigtails. Oddly enough, the Denso upstream sensors came with connectors, so I didn't have this problem. The pigtail was 2 black, 1 blue, 1 white, which according to the product insert, white is ground, blue is signal, and black is heater. Before I start cutting and splicing, how do these correlate to the pin-outs on the plug of the original sensor? From the service manual:


Am I correct with the following assumptions:

1 & 2: Black
3: Blue
4: white

 

If they didn't come with pigtails, you got the wrong sensors, you got the Universal ones. You need to get the Exact Fit ones. DO NOT cut the OEM harness. O2 sensor circuits can be very sensitive to any splicing of the wiring. Return the ones you bought and get the correct sensors.

 

According to RockAuto, this is the correct part: Denso 234-4260 ($43.79)

I sadly can't use the parts lookup tool at www.densoautoparts.com because their system is borked right now, it's running slow as hell and won't get past the step of picking "Tundra" for me. But I did confirm this is correct at AutoZone's website also, for 2WD and 4WD (sometimes those are different) so feeling pretty confident on this one.

 

I got the Denso's (

$47 234-4260 Oxygen Sensor

234-4260); no pigtails and factory installed connectors. Took 10 minutes to install, fired it up and no MIL. Drove around a couple of weeks to break them in and all it well. @shifty` I owe you a beer. Thanks much