water temp sensor

[supraman7mgte]

Can a bad water temperature sensor affect the functioning of the egr sysrem?
I have replaced the egr and modulator and am srtill getting a code 71.
I do think the water pump is failing if that helps.

 

[jetjock]

Can a bad water temperature sensor affect the functioning of the egr sysrem?

No.

 

[jdub]

Check the EGR gas path through the intake manifold channel. As JJ said, no way the coolant temp sensor is at fault.

 

[BlackDevilSupra]

Would make logical sense that after ~4yrs of community participation, one would learn about the value of the online TSRM, and specifically the EFI diagnostic section therein.

 

[devrainey]

when i had first gotten my suppy the water temp sens was busted... i mean it had litterly been busted and my car had a very hard time starting. I replaced the sensor and BAM!!! no more hard start. If its not hard starting then id assume your sensor is fine.

 

[supraman7mgte]

Well I checked that section,and at the very bottom it had a part about testing the water temp sensor.
I don't know if it had anything to do with affecting the EGR,and that's why I asked.
The only thing left is the EGR temp sensor and the VSV.
I'll be checking those this weekend.

 

[jdub]

Might want to read what a code 71 means again

 

[devrainey]

egr sensor? is your car originally a cali car? because mine has no such sensor, but im from ms and we have no emission laws here. i just disconnected my egr and noticed no difference at all.

 

[jetjock]

Only Cali cars have EGR monitoring.

...at the very bottom it had a part about testing the water temp sensor.

Hmmm. So it does. Standby while I look into that more closely...

 

[hvyman]

Check the EGR gas path through the intake manifold channel. As JJ said, no way the coolant temp sensor is at fault.

a clogged egr cooler im assuming would be part of this? those things get caked with carbon after the years go by.

 

[TurboStreetCar]

EWD says the EGR system uses water temp, TPS, and AFM to control it. Makes sense as i would assume the engine would need to be at operating temp before the EGR is functional.

Source: http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=45

I like the EWD because it has explanations of each sensors function and how and what is is used for on each system.

Code 71 is for EGR temp. Check the EGR temp sensor and make sure that flow can be attained threw the system, as JDub said.

Check here: http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=118

 

[devrainey]

very possibly. to check vsv:

 

[jetjock]

Anything that prevents the exhaust stream from reaching the sensor can cause it as can a bad sensor or wiring. There's a lot of leeway in the software though. It allows for up to 4 minutes of sensing and the code is two-trip logic.

OP: The coolant sensor doesn't effect operation of the EGR system but it is involved with processing the code. For 71 to be set several prerequisite conditions must be met and one of them is a coolant temperature of more than 149 degrees. It shouldn't *cause* the code though so why they suggest testing it isn't clear. That said it's unlikely to be your problem. What is likely to be the problem is what Jdub said.

Don't blame him btw...I have better documentation than he does.

 

[jdub]

The coolant temp sensor is one of the parameters the ECU uses to cut off the EGR to maintain driveability...coolant temp must be above a set temp for the EGR to function. RPM is another - the EGR does not function at idle (controlled by vac port placement), nor above 4000-4500 RPM (ECU controlled via the VSV). The ECU also shuts off the EGR when intake air volume exceeds a predetermined level per engine revolution or when fuel cut-off occurs.

Like I said, take a look at what code 71 means and what potential problem areas it points to....hint: EGR gas flow is one of them.

 

[supraman7mgte]

I remember seeing a section where it had all codes and thier meaning.
I'll have a look to see if I can find it.
Thanks everyone for your input!
Just curious if Supramania members still get a discount at Jay Marks Toyota!

 

[jetjock]

I only checked the code setting parameters. It may be the VSV is inhibited until 149F is reached but to know for sure I'd have to look at documentation I don't currently have with me. As Jdub said the other sensor references involve inhibiting EGR (via the VSV) above a certain speed, throttle angle, and load. Since they deal with having the EGR off they're not involved with setting your code...

 

[TurboStreetCar]

I remember seeing a section where it had all codes and thier meaning.
I'll have a look to see if I can find it.
Thanks everyone for your input!

This? http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=26

 

[hvyman]

same thing but no going threw 5 pages to get to it.

http://cygnusx1.net/Supra/TechTips/engine_error_codes.aspx

 

[supraman7mgte]

THAT'S the one I saw! Thanks!

 

[jetjock]

Notice neither of those mention the coolant sensor as a possible cause. Nor do they tell you the actual parameters. The reason for that is the same as why I don't usually go into them even though I have stuff that puts anything in the TRSM, TWED, or anything else ever posted here to shame: knowing the details isn't very useful and they can't be changed. They are what they are. Following the guidelines in the code list alone is usually more than enough to fix the car.