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2002-2005 Range Rover MkIII / L322
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Discussion Starter #1
I have a check engine light and three codes that I have erased a few times but they keep coming back. Two of them are are 02 sensor bank 1 and 2, downstream. So, I removed the rear most 02 sensors and cleaned them and reinstalled. I figured I have nothing to lose by trying that. I will order new sensors if this doesn't work. The final code is electric thermostat circuit fault. Any idea what that means? Do I need to replace the thermostat? Is there any testing I can do on the circuit itself? The temp seems fine and the coolant level is fine. Thanks.

Silver Rover
2004 Range Rover HSE
 

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2002-2005 Range Rover MkIII / L322
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71 Posts
Discussion Starter #2
It's sure quiet on here. Just a little update: One of the downstream 02 codes came back so I will just change both rear 02 sensors. Also, the Electric Thermostat Circuit Fault code came back. I guess I'll change the thermostat and hope that it solves the check engine light - unless someone has suggestions for checking other things. I would hate to throw a new part at this if it isn't the actual problem. Does anyone have any insight on this? Thanks.
 

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1,423 Posts
How did you clean the O2 sensors?

Have you checked your cats for leaks?
There is a whole history on the catalytic converter leak problem.
 

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2002-2005 Range Rover MkIII / L322
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127 Posts
Are the O2 sensors you have the original ones? How many miles do you have on your truck?

I replaced the front 2 sensors when I got the codes 3 months ago and everything's good. I have 135,000 miles on my truck. The sensors were the originals. Gonna replace the other 2 next month.

I also had the thermostat code earlier this year. You gotta be careful with that one because the thermostats are heated and even when they fail, electricity still runs to it. This could cause you to burn out that harness... not good.

I replaced my thermostat and haven't had that code since.

I have a question for the posters here, why is the thermostat heated?
 

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2006-2009 Range Rover MkIII / L322
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1,148 Posts
So the ECM can control the opening of the thermostat under certain conditions before the water temperature opens it.
 

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2002-2005 Range Rover MkIII / L322
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71 Posts
Discussion Starter #7
Thanks for the comments guys. I wasn't aware of the catalytic converter leak problem. I will research this too. I am not sure of the DTC codes. I have the Icarsoft scanner and all it stated was:

"P0000 sensor ageing fault, downstream fuel trim bank 1. Last occurrence-plausibility".
"P0000 sensor ageing fault, downstream fuel trim bank 2. Last occurrence-plausibility".
"P0000 electric thermostat circuit fault. Last occurrence-plausibility".

I do not know if they are the original 02 sensors. My rover has 120K miles. I removed the rear two 02 sensors (based on the description of the codes) and cleaned them with brake cleaner. All three codes came back the same day. After erasing the codes again, none of them have come back in several days. Kind of strange.
 

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I didn't know you could clean O2 sensors with brake cleaner. They're real sensitive, and I've always heard just to avoid any contact and keep them from contacting anything, which is why they have the guard around them.
 

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2002-2005 Range Rover MkIII / L322
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Discussion Starter #9
I don't think you can clean them either. I knew I was going to replace them so i figured it wouldn't hurt anything to try and clean them.
 

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2002-2005 Range Rover MkIII / L322
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Your engine came with an electronically-controlled thermostat. That code usually means that the electronic component is malfunctioning, and usually entails replacement of thermostat. I'd replace water pump while there, if not hasn't been done.
 

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2002-2005 Range Rover MkIII / L322
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Discussion Starter #11
So I replaced both rear o2 sensors and the check engine light continues to come on for bank 1 and for back 2 - so no change. Therefore, I am not sure what the issue is. Someone had mentioned leaky cat converters - I don't know what to look for but I'll do a little reading on that. Any other suggestions on what to look for or what else could contribute to these codes reappearing? Thanks.
 

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I am on my cell and do not see your model on the page. If a BMW one it could be an issue with that tstat wiring as well as engine coming up yo temp too slowly which could be faulty temp sensor or faulty tstat tir trans cooler circuit. On ours I get a p0128 code and if I dont erase it I get the 171 174 p codes. Is that what you are getting
Please add full description so even some of us less talented can chip in with good support and less speculation since we have been assisted numerous times. Cheers.
 

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1970-1995 Range Rover Classic
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455 Posts
We often surpress the thermosthat function here, leaving it permanently open, due to our climate.
Guess in Florida or southern california it would be similar.

The downstream O2 sensor error is NAS specific. it makes absolutely no differnce in emission tests. We have one in right now that ad this error for two years and it flew through the tests with full marks. In the rest of the world, they are not neccesary.
 
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