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Discussion Starter #1
I recently purchased a 2001 Automatic Xterra SE (xtreme).
Since I bought it (2 months ago) there has been a smell that resembles burning coolant. I'm not leaking coolant but every 100 miles or so I need to add about a cup of coolant in the resevuar.

... my biggest fear was a cracked Head Gasket but there are no other signs of this so I decided to put it off... (a problem of mine).

Last week while pushing the throttle pretty heavily on the interstate my SES light came on. Lastnight I had it read by an auto parts store and it read P1126, the guy simply said "You have to take it to the dealer for this one".

Then the code reader actually got stuck on the connection in my truck, he couldn't remove it and when I pulled it off I broke his reader and we went our seperate ways.

I've researched it a little and keep coming up with a faulty Thermostat. If this is going to fix all my problems I would be estatic but it's never that easy.
I'm noping the Thermosat is faulty and is leaking coolant from that point.

1. If I simply replace the thermostat first, and then reset the SES will this cause any future problems?

2. are the 3 problems related (smell, 'using' of coolant, SES P1126)?
 

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I'm going to say yes, they're probably related. However since I don't know the actual meaning of the code I'm guessing it could have been an overheat code.

I'm thinking you're going to have to burp the coolant system by undoing the bolt on top of the upper intake and filling the radiaor until coolant comes out of the upper intake bolt hole.

You are going to have to pressurize the system to find the leak. A common place is all the useless spring clamps on the hoses. Replace them with screw type hose clamps. The radiator cap is another.

Obviously keep an eye on the coolant level, make sure you don't have coolant in the oil (the oil will look like chocolate thickshake), check the exhaust for sweet antifreeze smell, both of these indicate headgasket failure.

Look for the easy stuff first.
 

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Discussion Starter #3
Much appreciated.
I might just replace the Thermostat this weekend and see if there are any leaks in this area. I haven't noticed any smell from the tailpipe (just coming through the vents but I can't place it's location in the engine. also there are no visible leaks) and the oil sill looks like oil so that's promissing.
Coolant is being monitored. I hope to resolve this soon.
 

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Is the passenger side floor damp? That would indicate the heater core if it is.

My money is on the clamps, particularly the hard to get to ones for the heater hoses. I wouldn't bother changing the thermostat, just get the leak fixed.
 

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Discussion Starter #5
Luckly the floormatt's are dry.

I guess I can hold off on the Thermostat... although it's a cheap fix and fairly easy to get at so I figured I would just pull that out and hopefull the take care of the leak at the same time if it was coming from there.

however since I don't see any leaks and I'm guessing it only really likes when driving I'm going to have a hard time finding the exact location.

Thank you for your help and suggestions.

I will be looking into this over the weekend.
 

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Discussion Starter #6
Hopefully after presurising the system the Leak presents itself.

I'm guessing I just remove the mount that I put in when I'm done with the test?

Regards
 

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try looking under the intake manifold. it is common for the intakes to leak and if its leakin on the motor it will burn off before it hits the ground. Could be where the smell is coming from.
 

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Look at your throttle body. There's a wax pellet under the throttle linkage for cold start open throttle position. If that pellet is leaking, it will leak onto the left exhaust manifold, giving you a smell.

The code P1126 is for T-stat function. This could also be due to a bad temp sensor for the ECU, not the sensor for your gauge (different sensor). So double check that you don't have corrosion on that sensor (yellow sensor with 2 wires, located at the upper hose goose neck, at the front of the engine).

If you have corrosion on that sensor, it could also get you worse fuel mileage as well. The t-stat could also be bad as well. I'd also check the water pump to see if it's leaking. Could explain being low, like the wax pellet.
 

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Discussion Starter #9
After pressureising the system I found the leak to actually be at the underside of the main hose coming out of the radiator. A new Hose and some clamps and it appears to be taken care of. the leak was actually getting less and less as I drove it which was wierd but I decided to replace the hose anyways.
I will report back if the smell continues.

I also reset the SES light and it hasn't come back on yet but I've only driven 5 miles...

I'm waiting to replace the T-stat until I know it's bad... it seams to heat up just fine. Even when it's 0degrees outside it's up to temp in 3-4 miles.

Thanks for the help.
 

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Did you burp the system? The code could have been caused by the ECM getting weird readings caused by the sensor being "out of the coolant".
 

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Discussion Starter #11
Did you burp the system? The code could have been caused by the ECM getting weird readings caused by the sensor being "out of the coolant".
I did and that's how i found the leak in the hose. I noticed it was leaking there earlier but it was such a small leak i figured it couldn't have been the main cause but I guess it was. Things seem to be in order now but after re-setting the light it came right back on so that wasn't it.
Like I said, I had Advanced run there brief DINO for free and it came up with a code that reflected thermostat issues but everything seems to be in order. I might have the garage run a more thorough diagnostic ($90 but they "say" there's is "much" more intense than an auto parts store) but i'm sceptical of forking over $90 (dealer is $100).
Getting off topic, my gas milage is down around 11mpg so i'm thinking it's worth the $90 either just to figure that out. new plugs/wires/rotor/cap/airfilter/plugs and it barely did anything.... that's a whole nother thread.
Thanks for the help.
I hope I didn't pick up a Lemon.
 

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Sorry to be a new member and bump an old thread, but after using google for several months trying to find out what this P1126 ment, I finally got it fixed.

For the last 2 months, I had the service engine light on, poor gas mileage, and slow temperature rising.

I tried replacing the Coolant Temp Sensor (cheap and easy), but that didn't work. So, I bit the bullet, took it to the Nissan dealership and had them run the code and fix the problem...

...the answer? The Thermostat was stuck OPEN! Guess thats why it was running descent enough to drive it, but was the reason I was having those symptoms!

Just wanted to contribute to the boards for future google searchers that were looking for an answer to their 01 Nissan Xterra P1126 code
 

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Thanks for that info. Coolant/temp problems suck to deal with. I deal with them on every rig I've had...and this one has been no exception.

Useful info though...I had two problems with mine: a bad thermostat and a bad upper radiator hose...after those were fixed the truck runs fine now.

For anyone else wondering; these are problems that you don't want to put off. An engine that runs hot doesn't last as long and can lead to bigger problems (head gaskets, blown hoses, etc...). So, fix the easy, inexpensive stuff first before it leads to more headaches.
 

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Discussion Starter #14
Pathtek4 -

Thanks for the information. What did the dealer end up charging you for that repair?

I've still got the issue. Did they simply replace the thermostat?

You weren't by any chance also throwing the P0325 code as well were you?
 

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I guess I'm going to have to replace my t-stat then...

I had this same thing happen back in february, no one could tell me what the code meant. It had the p1126, and one for the knock sensor.

Advance says "manufacturer control, air fuel metering" Autozone says "Throttle Control Motor Relay Open"

Neither of those descriptions are useful at all, the first is way too vague, and the latter, well a 2001 Xterra does not have a Throttle control motor, as it is not "drive by wire", thus it should also not have a relay for that either... so we were all left scratching our heads on that one...

Anyway, I cleared the code out back in feb, all was fine until today it just came back on on my way to work. You know, I had noticed it's taking longer to get up to temperature lately, but I hadn't thought anything of it... I guess I will just pick up a t-stat and give it a try. Last summer I did have a couple of traffic jams that caused it to overheat, so a stuck open thermostat makes sense... but how does the computer know that?
 

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A computer knows how long it has been running, and it can read temperatures. It puts those two facts together.
 

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when you replace the thermostat there is a small plunger on the side that must face up or you have to re due it a second time.
 

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Ah HA!

From the Nissan factory service manual, Section EC, Page 1047

"DTC P1126 Thermostat Function:

On Board Diagnosis Logic

Engine coolant temperature has not risen enough to open the thermostat
even though the engine has run long enough.

This is due to a leak in the seal or the thermostat open stuck.

Malfunction is detected when the engine coolant temperature does
not reach to specified temperature even though the engine has run
long enough.

POSSIBLE CAUSE

 Thermostat function
 Leakage from sealing portion of thermostat
 Engine coolant temperature sensor "
"

So, now all I wonder is why the parts store computers don't have the code right...

I guess I'll pick up a t-stat and swap it out. Hmmm... so for the past 8 months my truck has thought it was running too cool, which means it was running richer than it should have been, which would explain why my gas mileage has been crappy!

Yup, this is on my to do list for sure.
 

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i think the 2001 had a lot of changes in mid year ,you need to look on the door jam and decide if you have a early 2001 or a later 2001 that is more of 2002.im thinking you have more of a later 2001 and the codes dont match for your year.
 

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lately my X has taken longer to warm up in the mornings. Takes about 5-7 miles to reach operating temps. Think its worth swapping out the thermostat? Im getting around 14mpg as ive always gotten. Its never overheated, or gone past the halfway point on the temp gauge. Also, whats the correct part number for the thermostat?
 
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