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Discussion Starter · #1 ·
Hi all,

Any help would be much appreciated. I have a MK 1 Megane 1.6 16 v cabriolet 2001 I believe, and I noticed last week some wiring hanging below the car. Turns out that it is the wiring from the loom and the rear o2 sensor. The plug that connects them is missing so I just have the wires. On the sensor side I have 2x white, a black and a grey wire, and on the loom side a brown, a green, an orange and a pink wire. Can anybody tell me which wires connect to which? Thanks in advance.
 

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With sensor connector missing you should have Check Engine light on.

Two white are heater so should be 12 Volts and chassis.
Black and gray are signal wires, connected to the other two coming from front of the car.

You can not solder them, they have to be mechanicaly connected.
 

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Discussion Starter · #3 ·
With sensor connector missing you should have Check Engine light on.

Two white are heater so should be 12 Volts and chassis.
Black and gray are signal wires, connected to the other two coming from front of the car.

You can not solder them, they have to be mechanicaly connected.
 

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Discussion Starter · #4 ·
Thanks Moxinel,
Very much appreciate you helping me and others out on this. Shows the real value of great sites like this and people reaching out to help others with problems.
Does it matter which of the two remaining wires from the loom, the black and the grey wires are connected to?
 

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Technical Supremo.
Scenic II, 2004, K4MW761, DPO
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The O2 sensor contains 2 sets of wires as already mentioned. The heater wires are isolated from the actual output sensor wires.

From the info I have here the Green and Orange wires are heaters (connect to the 2 whites on the sensor - doesn't matter which is which)

The other 2 are actual signal wires - no idea on the diagrams what goes where but in theory there are only 2 choices - so if one choice doesn't work just swap the 2 wires over.

Also - as mentioned - you shouldn't solder these - Bosch et-al makes proper watertight mechanical joining kits or if you cannot find those crimping ferules (tubes) with sealant and heat-shrink also will do the job
 

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Discussion Starter · #6 ·
The O2 sensor contains 2 sets of wires as already mentioned. The heater wires are isolated from the actual output sensor wires.

From the info I have here the Green and Orange wires are heaters (connect to the 2 whites on the sensor - doesn't matter which is which)

The other 2 are actual signal wires - no idea on the diagrams what goes where but in theory there are only 2 choices - so if one choice doesn't work just swap the 2 wires over.

Also - as mentioned - you shouldn't solder these - Bosch et-al makes proper watertight mechanical joining kits or if you cannot find those crimping ferules (tubes) with sealant and heat-shrink also will do the job
 

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Technical Supremo.
Scenic II, 2004, K4MW761, DPO
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Let us know if the printed info actually will agree with operations on the car :p
 

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First find a wire with 12 Volts ignition on.
Two more from the car should be ground.

Usually green is signal wire in Renault cars.
So 12 Volts and 1 ground (orange or pink) should be for the heater (2 white on sensor), green and brown should be signal.
 

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Technical Supremo.
Scenic II, 2004, K4MW761, DPO
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Well - here we go ............... Wiring colours and published diagrams - I am referencing Renault's Visu system
 

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Discussion Starter · #12 ·
Thanks guys. Will test wires for 12v and ground and come back to you with results. Thank you again.
 

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Discussion Starter · #13 ·
Ok. I used a test light to do the following: I connected the test light to the negative battery terminal and switched on ignition without engine running. I then probed the four loom wires and found that the brown wire was 12v. I then placed the test light on the positive terminal and found that the green wire was a ground. The other two wires ( pink and orange ) didn’t register anything. These are the only checks that I’ve done as I have a very basic understanding of electrical systems and don’t want to damage the engine control unit. Does this help identify which wires from the loom connect to which wires on the o2 sensor? I know I’m being over cautious, but I can’t afford to damage the car as it’s the only one I’ve got. Cheers guys.
 

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Technical Supremo.
Scenic II, 2004, K4MW761, DPO
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This is exactly why I asked you to confirm what you found on the actual car ............ There is/was a tendency NOT to follow wiring published diagram colours.

I would question only one thing:

The heater on the O2 is often NOT energised until the engine is running (function of the specific firmware on the ECU) - so I would repeat that experiment with a running engine - if the results are exactly the same, then I think you have found your particular vehicle's wiring diagram's colour convention for the O2 - ie - use pink and orange to supply the signal with brown/green feeding the heater.

If the wiring choice is correct then the O2 will produce about 0.46V while the engine is idling and still in open loop (first 30 seconds after start) - once closed loop is entered anything between 0 and 1 V if all is well
 

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There is/was a tendency NOT to follow wiring published diagram colours.
Is that about my post?
Check again.

I was guessing matching colours, said that has to be checked and specifically wrote that picture of my car is of no help since wire colours of the car are completely different.
 

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Technical Supremo.
Scenic II, 2004, K4MW761, DPO
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Is that about my post?
Check again.

I was guessing matching colours, said that has to be checked and specifically wrote that picture of my car is of no help since wire colours of the car are completely different.
No - nothing to do with you specifically or your post.

Check on this forum the number of times wire colour conventions were quoted citing official documents like Visu and then a totally different colour scheme was followed/found on the car that didn't even remotely resemble the quoted colours
 

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Discussion Starter · #18 ·
Ok. Completed above tests again but this time with engine running. Same results as before. 12v at brown wire, and green showing ground. Nothing from the orange and pink.
 

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Technical Supremo.
Scenic II, 2004, K4MW761, DPO
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Go for it then and I will have a beer on your reported succes
 

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Discussion Starter · #20 ·
Thanks. Will come back to you with some feedback when sensor is connected. This post will definitely be useful to anybody with the same car and the same problem. Many thanks again.
 
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