Engine wiring diagrams colors on the junction connector coming from the PCM

REALESTATEBROKER1

MEMBER
2011 HONDA CRV
4 CYL
2WD
AUTOMATIC
150,000 MILES

I replaced my two old o2 sensors recently with two new OEM (up and down stream) sensors. I however noticed a discrepancy in addition to having an 1157 obd2 code now. My new upstream o2 sensor has one white wire (i guess ground), one blue wire (i guess signal) and two black wires (heater). I measured 1.9 ohms across the heater. The colors on the junction connector coming from the PCM (and ultimately connecting with the o2 sensor connect-block), are different (2 red wires, 1 green and 1 white), which is cool, but the 2 red the wires coming from the car’s PCM are lining up with the white and black wire on the o2 a/f sensor and the green and white PCM wires line up with the black wires on the a/f o2 sensor connector block (please see sketch). I am confused, how can the 2 PCM red wires connect with the white and blue on the o2 sensor and the green and white with the black wires on the o2? Based on the way the colors are lining up, I need to conclude that one of the PCM red wires is a signal wire and the other red a ground wire, while the green and white wires would be for the heater? To me this does not make any sense? Can anyone explain this to me. Thanks.

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4 Replies

JIS001

MECHANIC
3,408 POSTS

Hello and welcome to 2CarPros. The A/F sensor wires are always different from the actual engine wire harness side to simplify diagnosing. If you have a heater circuit fault, check fuse #11 15A if fuse is good then verify you have battery voltage at the white wire with black stripe. You need an assistant for this because it will only come on for a couple of seconds with key on engine off. Here is a guide to help check the wiring with the engine wiring diagrams below.

https://www.2carpros.com/articles/how-to-check-wiring

What I am concerned with is the ohms you measured. That is pretty low? A cold sensor should measure more like 12 to 16 ohms. Now my question for you and please do not take it the wrong way, did you install an oxygen sensor or an air fuel ratio sensor for the upstream (before the catalytic converter)? I ask because there is a big difference in price. If you installed an air fuel sensor then that sensor alone should have been around $200.00+ if it is an A/F sensor then I would say you got a defective one because of the low reading. I attached a wiring diagram for you. Check out the diagrams (Below). Please let us know what happens.

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Wednesday, September 18th, 2019 AT 10:54 PM

REALESTATEBROKER1

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Hi, thank you very much for your reply. No, I am not offended about your question, but I do know the difference between an a/f and o2; the upstream is a/f pre catalytic converter dealing with a?F ratio and the o2 is post catalytic converter measuring the health of the catalytic converter. Also, in my case, I could not possibly install the wrong sensor, because the wiring quick disconnect block between the upstream and downstream are completely different (different connector's locking mechanism), so even if you don’t know much about this issue, you can't accidentally interchange them on the 2011 Honda cr-v. So, I may have received a bad a/f sensor, that thought crossed my mind quite frankly, because like you said, the ohms reading is indeed on the low side. I did check the fuse (#11) already, was the first thing I did and it was (is) good. Question: the cold ohms reading is obviously different from sensor to sensor, do you know by any chance what the correct reading should be for a cr-v a/f sensor? I tried to google it, but no luck.

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Thursday, September 19th, 2019 AT 6:57 AM

JIS001

MECHANIC
3,408 POSTS

Hello and welcome back. I am sorry but I do not have the spec for the heater element? As stated earlier, most vehicles I see something around 12 to 16 ohms. Is this a Honda A/F sensor you installed? And as for my earlier post, I did not mean to imply you swapped the sensors from front and rear. There are actually upstream oxygen sensors sold. My sister had an Accord after she replaced the A/F sensor from a local mechanic working from his backyard it was giving all sorts of problems. I looked into it and it was an oxygen sensor installed instead of an A/F sensor. Told her how much it was and she said no wonder the part was cheap lol. You may want to call Honda and ask the parts department if they have the specs? Sometimes they will ask there techs. Worth a try?

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Thursday, September 19th, 2019 AT 9:16 PM

REALESTATEBROKER1

MEMBER
8 POSTS

Okay great, thank you very much for your insight and thanks for the wiring diagram as well; the schematic helped me a great deal. Where can I get meaningful diagrams like the one you sent me if I may ask? I signed up with a site (free diagrams site), but the diagrams are limited in scope. Finally, a related question, I found another electrical box inside my car sitting on the floor behind my steering column, it almost looks like a mini PCM, what is this box about (see picture? Thanks

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