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Discussion Starter #1
Hi Folks!


Just wanted to share that today my car gave me a friendly warning on Warming it up!

I needed to go out in the early morning to do some business but my Wife needed me to do some quick shopping first at my local groceries, I did something I do not normally do... I fired up the car and without any kind of warming up I set off (Car was still idling in the high 1000-1100RPM), It was a less than 2 mile trip everything went smoothly and I went back home and finished preparing..

I go back to my car now ready to start the day and when I started the car I was greeted in less than 1 minute with a HUGE "CHECK EMISSION SYSTEM: P0134" & AWD System Disabled SH-AWD: 77.... Needless to say I was very worried hahahaha. I did some fast research on the iPhone and I found out it was a problem with the Cat which was alarming since I passed inspection in freaking California not but 3 months ago. If the Cat goes bad for some bizarre reason it disables the SH-AWD System.. Then I realized I didn´t warm up the car at all and I recalled the MDX ala most Acura & Honda products runs super rich at startup... I told myself "Isn´t the cat just soaked in gasoline and its throwing the ECU Off?" Well Ill be damned that was the issue!!

How to fix it..
1.- Just let the car get to working temperature so the Cat can get hot and burn the excess gas.
2.- Turn it off and remove the negative battery cable to reset the ECU (Have your Stereo and NAV code in hand).
3.- Put the cable back on and fire up! No more nasty emission codes and SH-AWD back in operation.


So that is it guys! if you ever get a SH-AWD code 77 with a Check Emissions P0134 try to recall if you warmed up the car before setting off.. Odds are your impatience was rewarded with some hardcore OBDII Justice.
 

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Damn, I got the same thing about 2 yrs ago and I replaced that AF sensor and I thought that took care of it. But maybe I simply wasted 100 bucks?

The code P0134 is pointing toward the sensor, not the Cat. So I am very interested in your thought process. To me, sensor circuit no activity has nothing to do with the Cat. That is why I am totally shocked that the problem can be solved this way. Any analysis would be really helpful.

Keep up posted. Thanks!
 

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P0134 ACURA - O2 Sensor Circuit No Activity Detected Bank 1 Sensor 1

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

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Discussion Starter #4
The ECU calculates the difference between the front bank and the rear bank O2 Sensors.. if the cat is throwing a bad signal it will first try to test the 02 sensor read vs the rear and front once they show a big difference in output the ECU will say that the o2 sensor is faulty.

For the ECU to say the Cat is bad it will need to show that both bank of sensors are showing a bad signal which they weren't.
That added to the fact I didn't warmed up the car was my line of reasoning to think this was a false code.

I have driven all day now and the problem hasn't popped up again.
 

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Thx for the reply. But ur explanation isn't clear to me. That code means ecm got nothing from the front sensor. If cat is at fault, computer would receive SOMETHING from the sensor. Let's see whether the code will come back or not. Maybe there is another story.


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It is not the cat, sensor problem. Your sensor probably failing, maybe wiring...
Sensor before cat, the hard to reach one back.
 

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Discussion Starter #7
Well I dunno how to explain it better but no worries.. They aren´t malfunctioning as I said before I passed inspections 3 months ago in California... If something were slightly just ever so slightly amiss I wouldn´t have passed Inspection ever. The issue here was because of the warm up and the rich start up behavior of the car.

Code hasn´t come back and its highly unlikely my o2 sensors went bad. My TL-S is still rocking its 16 year old 220,000 Miles original o2 Sensors and I have yet to replace an o2 Sensor in a Acura & Honda product ever... They can go bad for sure but the sensors weren´t the problem today.

I Created this Thread to give a Tip for anyone that has those 2 Codes go up randomly so they had a north on what to discard... But thanks for giving suggestions on repairs.
If the code do come up again I will update this thread, But the issue was the Warm Up.
 

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Discussion Starter #8
Just wanted to say there weren't any codes today either! But thanks again for chiming in for fixing answers.
 

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Discussion Starter #9
Well after these couple months of Check Engine free rides yet again the P0134 popped in today after I went for a fill up..
Seems that perhaps back in march it was starting to Act Up but decided to give me some months of work (Haven´t seen any changes to MPGs). So time to replace that o2 sensor I guess... Time for a Little DIY guide too perhaps?
 

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I had the P0134 code pop up twice in the past 6 months or so … the first time in February and the second time a week or two ago. The code went away after a day or two. Nothing seems to be out of sorts.
 

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This is a good guide. But I did not remove anything like spark plug wire etc. I just used my left hand and reached the sensor from the left side of the engine. The whole thing took me about 20 minutes to finish. But I did spend like 2 hrs trying to understand how the sensor is attached to the bracket with a flashlight and a mirror. The key is to press on the clip and pull it downward.

Also you'd better take care of it. Two or three years ago a guy who neglected this light for a long while reported that his car could not even move.
 

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Discussion Starter #12
I had the P0134 code pop up twice in the past 6 months or so … the first time in February and the second time a week or two ago. The code went away after a day or two. Nothing seems to be out of sorts.

I haven´t seen a single change in MPG performance either but It is important to notice that this upstream sensor is both an o2 sensor and a A/F Sensor which means this little sucker is way too important to be neglected.
So even if there hasn´t been a change in MPGs I will change this expensive sucker as preventive maintenance ASAP.
 

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Discussion Starter #13
https://www.youtube.com/watch?v=G_JMPWPw7mQ

This is a good guide. But I did not remove anything like spark plug wire etc. I just used my left hand and reached the sensor from the left side of the engine. The whole thing took me about 20 minutes to finish. But I did spend like 2 hrs trying to understand how the sensor is attached to the bracket with a flashlight and a mirror. The key is to press on the clip and pull it downward.

Also you'd better take care of it. Two or three years ago a guy who neglected this light for a long while reported that his car could not even move.

Man NICE! Thanks for the video! I noticed you replaced it with OEM, Do you happen to know which brand is OEM for Aftermarket? I thought it was DENSO but searching online it seems OE is NTK (NGK Brand of o2 Sensors).
And yeah I will try to take care of this ASAP.. But the part is expensive so strictly OEM is out of the question right now.
 

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NGK is OEM. Denso works well too. Both are $7x. NGK is slightly cheaper. In my experience, Honda/Acura always chooses the cheaper one among Denso/NGK. For example, OEM spark plug is Denso. Denso air fuel sensor is more famous. So we have NGK af sensor here.
 

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Sorry for reviving this thread. Yesterday My MDX just showed P0134 with 77 code in the morning for the first time since I own this one. My MDX is 136k.

This past week I drove short distance and the engine might not warm up enough. However, today the light still showed in the morning but once I drove on the highway for good 20 minutes and all of the sudden, I don’t know when, the light just went away. I will still keep my eyes on it. The cheapest price I found for NTK is around $86 at Rockauto, $120 at Autozone (need to order), Napa ($140) and $223 at the dealer.

I might order it with socket just in case I lose my AWD again lol.
 

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Discussion Starter #16
Yup the issue went away agter replacing the Upstream sensor.
 

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Yup the issue went away agter replacing the Upstream sensor.
Yep, the light came back so I did order the upstream sensor and socket to take care of it tomorrow. I check the location of the sensor today, an access to the connector is not at the ideal location. It is hard to see but i'll try.
 

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Discussion Starter #18
Its actually really easy to replace if you buy the correct Lisle socket? you can do everything by hand feel.. The hardest part IMO is to remove the sensor connector since it wants you to pull downwards looking at the firewall which is oddly placed.
 

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I just changed it today. I watched the YouTube from the guy who posted here. I didn’t listen to the video so I missed some info. Like you said, the hardest is to remove the connector on the back for the bank 1.

I just realized that when I pushed the button on the sensor side and I could slide the whole wiring down from the metal mount, after that It was easy. The sensor came off easily with oxygen sensor socket. I was very happy that I can get my SH-AWD back. Lol
 

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If anyone can help, I would really appreciate it if he can inform us the purpose of the 5 wires of different colors. The error message I got was sensor heater circuit is bad, it will be nice if someone can figure out a way to get the circuit to function again.

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