dhg2496

I appear to have a stuck thermostat, or at least that's waht the dealer thinks.

So first things first...would a P0125, closed loop fuel control insufficient coolant temp, be a thermostat problem?

If it is the thermostat...

I think I know where it is located. But does anyone have pictures of a thermostat replacement that I could use as a guide to replace it?

What is the toyota part number for the Thermostat?
What other parts, gaskets or special tools might I need to replace it?

Thanks for all your help, you guys are great!
Bill

Lexmex

I show 3 trouble areas out of the manual for P0125,

1. open or short in the A/F sensor circuit
2. the A/F sensor itself
3. ECM (not likely though...as other things would go screwy)

I do not see thermostat mentioned.

I have with my uncle replace the t-stat with the TRD sport model. I would not recommend it as a DIY as the procedure is a little bit complicated to describe and perform.

salimshah

The following applies only to thermostat/cooling. [ie not looking at error codes]. One has to account for fan assited cooling but tests are simple enough.

What does the temp gauge show?

I hope you can recall the normal op. temp gauge indicator position for your RX. Typically between around the middle of the range .. for my RX it is slightly above 2 ticks ~40% up from C. Prior history can help you confirm the diagnosis.

Does it take too long to warm up. [thermostat stuck open]
Does it climb to Hot [thermostat stuck closed]
Does it fluctuate but stays above the normal [restrictive flow]

The other more invasive way is to observe the coolant flow through the radiator cap opening, but there is risk of scalding. So it is better to take it to a radiator shop, who can run the checks for you.

Salim

dhg2496

Thanks, what manual do you use to get this information? I found a shop manual to actually change the thermostat but haven't been throught the rest to see if codes are listed as well.

The strange thing is that my problems started with the A/F sensor and I replaced that. Then about a week later I got a series of codes, 5 of them to be exact, that the dealer looked at and determined I needed a new MAF and a thermostat. They suggested that the P0125, meant a stuck thermostat and should be replaced.

My temp gauge doesn't seem to be reading any different than before the problem and has always read just below half way. I just figure that there must be more than one sensor reading coolant temps.

But hey with all the other codes popping up I just hope it's not option #3!

Lexmex

Volume 1 of the service manual listed this. Do you notice anything funny about the car in its performance?

dhg2496

Thanks for the information about the manual, I found a 2003 RX Manual in PDF format on line for $10 and it is pretty good as a guid for dissassembly information and part removal/installation.

Right now the vehicle seems to be running fine since leaving the dealer (who cleared all the codes). However the check engine light came back on again after leaving the dealer and I drove to work then home after leaving the dealer. I haven't done any other driving until I get the code read just in case it's a more serious code. Hopefully I can get the code read tonight and see if it's the same code or a new one.

Lexmex

OK, let me know the code when you have it.

dhg2496

Ok, so I got the codes out of the ECU at Autozone and they are all too familiar. P0300-Multiple Missfires, P0301-Missfire Cyl. 1, P0303-Missfire Cyl. 3, P1701-Left Bank Running Lean.

The car stopped shifting into over drive after the multiple missfire code was detected. So The car is going back to Lexus tomorrow morning. I'm beginning to think that the Air Fuel sensor is causing the problem but that is just my guess. Just curious but is the left bank the front side of the motor or the back side of the motor? I'm also assuming that Cyl 1 & 3 are on the left bank.

Any ideas are much appreciated as I would like to make sure that Lexus looks at anything that might be causing this while it is in for service again.

Lexmex

1 and 3 are on the back side, 1 being on the far left and 3 being in the middle if you are facing the engine from the front as you normally would.

P0171 usually accompanies misfires as it affects rich/lean air/fuel settings, so I won't read too much into that alone.

The misfires (and I had one not too long ago) can be caused by a bad ignition coil (in my case, but the vehicle would sputter), bad plug or bad injector (even clogged) as the most common culprits. My uncle added that bad gas (notorious down here, though recently it got much better on the sulfur level) can also throw a misfire. Sometimes when the tank gets too far down, it can dredge up the stuff at the bottom of the tank.

dhg2496

Well Lexmex, you are pretty smart!

After a day at Lexus they have determined that Cyl.1 has a bad injector. So it will be replaced today once they receive the part.

I have to say you are much quicker at diagnosing a problem than Lexus Tech's at the local dealer.

But in the mean time we are driving around in a 2007 ES 350, which is a pretty nice car.

Thanks for your help!

salimshah

I tottaly agree

Salim

Lexmex

Actually, I just used a ouija board...last time I rolled dice...perhaps I should try my luck in Vegas LOL

Lil4X

Nice long-range diagnosis, Lexmex!

If clogged injectors due to trash in the fuel system are a problem, I found that an in-line filter was a great help. I used them in marine applications for years - a spin-on type slightly smaller than the oil filter, that could be mounted in a handy location. They are Coast Guard approved for Inboard Marine applications, but UL approval requires a metal bowl, and would be safer, particularly with E-85 fuel. They were quite well made, could flow up to 190 GPH (size yours as appropriate) and had the additional advantage of knocking water out of the fuel as well as dirt and grit.

My first Suburban had only a tiny fuel filter -about the size of a cigarette filter screwed into the carburetor - and one tank of contaminated gas would clog the fuel delivery in about a week. Rather than chance an unknown aftermarket filter, I just mounted a marine filter I was familiar with on the firewall and plumbed it in - end of problem. The sheer size of the filter meant I could go a year or two without trouble - even with pretty suspect gas.

http://www.maesco.com/products/racor/r_gas/r_gas.html

http://www.boatbandit.com/detail.aspx?ID=4913

Discounted to about $115, with replacement elements around $30, it might be a whole lot cheaper than injectors.

dhg2496

I know what my next purchase is! Ouija board! Again thanks for the help, this forum has been alot of help in diagnosing the problems I've had.