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lexpert, Lexus Master tech
Category: Lexus
Satisfied Customers: 9974
Experience:  Master Certified with lexus, 8 years experience with Lexus
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1991 Lexus LS400: a code 71 :EGR malfunction..replacing..O2 sensor

Customer Question

Hello, i have a 1991 Lexus LS400. It is throwing a code 71 :EGR malfunction. Prior to this it had a code 25 and failed the etest (up here in Canada), which was fixed by replacing the thermostat and one O2 sensor (pre-cat). Then the etest passed easily, but code 71 appeared.   Could you tell me where to start looking to resolve this? The car runs fine otherwise, but i haven't had time to check the gas mileage yet. Thanks, Andrew   [email protected]
Submitted: 8 years ago.
Category: Lexus
Expert:  lexpert replied 8 years ago.

Thank you for using just answer. This can be caused by several things in the EGR system, most commonl;y carbon deposits, click the link below, the system needs to be tested:



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Customer: replied 8 years ago.
Sorry, i was looking/hoping for something more specific, such as which part/s that might have the carbon buildup, how to clean them, with what product, how to remove/replace, that kind of thing. I found better advice this time from a forum where another LS400 owner had the same problem, and explained everything he did until he fixed the problem. I'm a newbie, and while the service manual pages will be somewhat helpful, they are written for mechanics, not newbies, so are somewhat confusing. I did read one post earlier about code 25, and someone from this site said specifically it referred to the pre-cat O2 sensor(s), ie. replace one or both, and that was spot on! I do however, realize after reading about code 71, that the problem could be in any number of places.      Thanks for your answer, Andrew
Expert:  lexpert replied 8 years ago.
These questions are not a one-shot answer. For future refrence if you decide to post another question and need more assistance or better clarification please just send a reply and request further assistance, we are here to HELP you not confuse you. Understand that I do get customers that their skill ranges vary from not being able to even open a hood all the way to master certified mechanics, unless it's simple question it usually can take several replies. The information I provided you is a general overview, I have to post answers that are not TOO complicated or not too drawn out to try and please all skill levels, sorry if the information I posted was too technical, this is not my intent. Thank you for the reply to let me know.
Customer: replied 8 years ago.
Sorry about that. I should have given you an idea of my skill level. I'm definitely not a mechanic, but based on your info, and other info i've found, i will be able to R&R the throttlebody EGR valve and associated vacuum hoses and give them a good cleaning. I don't think i can remove and clean the EGR pipe (tube?) at the back of the motor (it recirculates hot exhaust gas back to the intake i think), it may be too much for me.     Thanks,   Andrew
Expert:  lexpert replied 8 years ago.

One last note on your last response (thank you for the reply by the way), the EGR pipe on the back of the motor is nothing to worry about on this. This is NEVER an issue for your stated concern, they do tend to crack and produce exhaust noise with mileage/age but will not cause EGR codes, also you would have to remove the transmission to access this pipe.

Your issue is most likely related to carbon as you indicated your theory was. The download I posted shows how the system is laid out and how it interconnects. Most liekly the EGR feed port that runs to the throttle body has backed up with carbon so once you get the EGR valve off be sure to clean out the port with intake cleaner/pipe cleaners/compressed air and most likely you will need a new modulator valve as well.

Good luck and thank you for using just answer, you are a valued customer to us and your positive feedback is always appreciated!

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