1992 Land Cruiser Code 71 update (3 Viewers)

[Scota4570]

After a full assault with the parts cannon I gave up on this EGR code. I normally reset the code with the fuse to make the dash light go out. During city and highway driving it would come back on after about 100 miles, give or take.

I have done some longer off road drives lately. This mostly at under 10 mph and on steep terrain. About 50 miles each outing. For some reason that kind of driving causes the dash light turn off and go away for a while.

Is this behavior of any diagnostic value?

 

[Marco Lau]

Per Jonheld:
Error code 71:
EGR gas temp below predetermined level during EGR operation.

Suspects are:
• EGR valve
• EGR hose
• EGR gas temp. sensor circuit
• EGR gas temp. sensor
• VSV for EGR
• VSV circuit for EGR
• ECU

Tests are on page FI-45 of the FSM.

 

[Scota4570]

Been there and done all of that. All items that were available were replaced. All wiring and voltages were checked. All vacuum tubing was replaced. The EGR is clean and in good condition, it tests good, no replacements are available. The factory manual diagnostic procedure was followed. The only thing I can not test or replace is the ECU. This appears to be a special California version with extra nonsense piled on.

 

[Marco Lau]

Been there and done all of that. All items that were available were replaced. All wiring and voltages were checked. All vacuum tubing was replaced. The EGR is clean and in good condition, it tests good, no replacements are available. The factory manual diagnostic procedure was followed. The only thing I can not test or replace is the ECU. This appears to be a special California version with extra nonsense piled on.

just remove the dash light.....

 

[jonheld]

Been there and done all of that. All items that were available were replaced. All wiring and voltages were checked. All vacuum tubing was replaced. The EGR is clean and in good condition, it tests good, no replacements are available. The factory manual diagnostic procedure was followed. The only thing I can not test or replace is the ECU. This appears to be a special California version with extra nonsense piled on.

Did you do the 3 temperature tests for the EGR temp sensor on page FI-79 specific to CA spec?

 

[Scota4570]

I do not remember. Doing an oil bath test. I did check sensors in water baths that were associated with the cooling system. I did buy a new denso EGR gas temp sensor and installed it. The EGRGTS sensor has power to it. Good idea to confirm it works right though. I'll check it out.

There are a bunch of temperature sensors. My understanding is that they need to play nicely with each other. Otherwise you get this code after multiple starts. It makes sense to me that the slow off road driving would make them behave differently.

 

[azusa]

Are you getting exhaust to the transducer?

 

[Scota4570]

Please explain in more detail.
Which transducer, where is it located?
Thanks
Scot

 

[azusa]

25870-61020 Genuine Toyota Modulator Assy, EGR Vacuum

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At the bottom port, you should have exhaust pressure. Not a crazy amount or else it'll burn up the modulator or sometimes called transducer. Did you also replace this part, while searching on the internet says discontinued but that could be wrong call your local dealer for more accuracy.

 

[Scota4570]

I did the testing of the EGR temp sensor as described in the manual. Pretty sure I already did this already. I think the more accurate readings were when the temp of the oil was slowly cooling. I used three thermometers. I tested both the original and the replacement sensor at the same time in the same oil. The results were virtually the same. The results were out of spec on both sensors. That makes me suspect my methods more than the sensors. Although, I worked as a laboratory chemist for 30 years, I am pretty sure I did it right. I checked my meter against a resistor switch box, the meter is very close. See attached data. The "going up" column indicates heating the oil. Going down is slow cooling. What do you think?

One thought I am having is about old wire and increased resistance. Could my slightly out of spec sensors be adding to old wiring and messing the voltage the computer sees?

 

[Scota4570]

25870-61020 Genuine Toyota Modulator Assy, EGR Vacuum

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At the bottom port, you should have exhaust pressure. Not a crazy amount or else it'll burn up the modulator or sometimes called transducer. Did you also replace this part, while searching on the internet says discontinued but that could be wrong call your local dealer for more accuracy.

I replaced it with a Denso 25870-66011 / 139000-3300. It works the same. The old one worked fine. Based on the testing procedure, the whole assembly and hoses works as it should when tested with the vacuum tool. The hoses are all free and not plugged.

They seemd to have discontinued the 1992 part number for the modulator. The one I got seems to be identical. Nothing changed when I swapped them.

Back in a while.
Scot

 

[jonheld]

Are you getting exhaust to the transducer?

It's not a transducer, it's a thermistor.

 

[Scota4570]

The inside of the EGR assembly is very clean, I cleaned it, twice. I verified function, it works properly, the diaphragm is in good condition. The passage way behind the EGR is clear.

 

[azusa]

It's not a transducer, it's a thermistor.

The thermistor is the temperature sensor to the computer.

It's not a transducer, it's a thermistor.

You're mistaken, 8941212010 this is the thermistor.

 

[Scota4570]

We are getting off track. My questions was, "I have done some longer off road drives lately. This mostly at under 10 mph and on steep terrain. About 50 miles each outing. For some reason that kind of driving causes the dash light turn off and go away for a while." For reference, that dash light indicates a code 71.

I do find it interesting that both of my EGR gas temp sensors give identical test results and the testing does not match the factory repair manual specifications. My understanding is that the problem is caused by temperature sensors in the EGR and cooling systems not working as the computer expects them to.

 

[azusa]

My understanding is that the problem is caused by temperature sensors in the EGR and cooling systems not working as the computer expects them to.

Do you happen to have a thermostat? On a cold day running down the highway what's your coolant temperature? You happen to have catalytic converters and are they OEM? The transducer needs back pressure, That's why I asked if that little outlet towards the bottom of the EGR puts out exhaust while the engine is idling, many times they are clogged with carbon.

 

[Scota4570]

Everything is as made by Toyota. I am a strong believer that I do not have sufficient knowledge to second guess the factory engineers.

The thermostat was tested and appears to work correctly. The system was flushed and the coolant replace about a year ago. The coolant temperature is correct based on the factory gauge. I have not added a separate gauge that reads the actual temp in degrees.

One observation is that the heater is slow to get going. The engine does take about five miles to get fully up to temperature. I attributed that to a partially plugged heater core. But.....this may be a clue. Running around the hills at low speeds and high loads would cause the coolant and engine in general to get hotter. Could the thermostat be jammed partially open?

A vent hole in the EGR? Where is that exactly? See attached photo.

 

[azusa]

9043043002 this part number is a seal that sits on top of the thermostat, so the thermostat housing takes a gasket, also this seal must be installed on top of the thermostat and then the housing. A good way to see if the thermostat or this seal was installed, start the engine cold, open the radiator cap. While looking inside the radiator if you see coolant circulating that will mean either the seal was not installed or the thermostat is stuck open.

 

[azusa]

From your picture, right above the threads towards the bottom of the EGR is that stainless steel pipe going horizontal, remove the rubber hose that's going to the transducer and start the engine. You should get exhaust flow coming out of the stainless steel pipe. If you have a small cable try to slide it in and out a few times.

 

[Scota4570]

The silver tube that goes to the EGR modulator is flowing free, not plugged. The coolant in the radiator is still when cold as viewed through the cap hole.