I have a ‘92 Lexus LS400 with 146,000 miles on it now. It runs great. I maintain it and am generally pleased with it. I keep eyeing the LS430, but having a car that is paid off trumps an LS 430 everytime.

My CEL started coming on last week. It is intermittent. It comes on for 50 miles or so, then goes off for about the same distance. I pulled the code and it is Code 71, which is ‘EGR System.’ I have scanned this forum and found other people with Code 71 issues, but no clear repair results.

I removed the EGR valve and EGR vacuum modulator and inspected them for build up of any kind. I cleaned all EGR related parts with intake manifold cleaner, though they didn’t look dirty. I blew clean air through them. I replaced the little filter in the top of the EGR vacuum modulator. I checked for air leaks in the vacuum lines. Nothing. The CEL continues to come on and later go off randomly.

I see from this forum that the parts in the EGR system include the EGR valve, EGR Vacuum Modulator, VCV, VSV, and EGR Temp Sensor. I’ve read that the EGR valve never goes bad. I certainly don’t want to randomly change these parts one at a time. Based on what I’ve written, what would be the first part to replace?

 

You did everything right but did you test to see if the EGR modulator and valve functioned according to specs?

 

Exactly where is the EGR temp sensor located? I thought I found it and cleaned it, but apparantly I did not.

I called the mechanic who replaced my timing belt and water pump. He used to work for a Lexus dealership, and knows Lexus well. I described my EGR problem, and he immediately told me that my problem was most likely the EGR temp sensor. He said he sees that problem frequently, and that is the first thing to look at.

Over the phone, he tried to describe to me where the EGR temp sensor is, but I cannot find it. He said it's right under the EGR valve, screwed into something else, and has a long pigtail. I cannot find anything like that. Does anyone here know where it is?

 

How do you check the egr modulator?

I checked the egr valve by putting a vacuum hose on it. The engine died instantly, which tells me the egr valve is good.

I found the egr gas temp sensor. After driving the car for 40 minutes, I checked the resistance on the sensor, which read 42.5K ohms. I don't know what the normal operating temperature range of the car is, so I have no way of knowing if 42.5k ohms is an acceptable resistance.

When I removed the egr valve and plate it's attached to, I found tons of gunk. I cleaned all the gunk out, but the check engine light still comes on intermittently.

How do you check the egr modulator?

 

http://www.lexls.com/tutorials/EFI/throttlebody.html

It explains in there that cleaning the throttle body may help...plus it's the easiest/cheapest route to go first for a CEL 71. It only costs like 3$ (throttle body cleaner) and about 1.5 hours of work.

Look into that before you go jumping into the actual EGR problems.

-Sean

 

Thank you for the recommendation Sean.

Today I removed and cleaned the throttle body just as recommended, using LexLS's tutorial (thank you Carl). After I put it back together, I poured Sea Foam in the Brake Booster vacuum line and drove the car for about 30 minutes. The check engine light came back on - Code 71.

My next step is to check the egr vacuum modulator? Does anyone know how to check it?

 

Screw it.

Delete it.

also read here if you're interested in more info.

Later!

 

I fixed my EGR problem! I removed the cap and filter, and soaked the EGR Vacuum Modulator in a glass of Sea Foam for about an hour. Then, I gently tapped it on the floor. A lot of black carbon specks came out of the hole on the top. I blew air through all the openings to dry it out and get out any more loose carbon. I’ve since driven it for over 200 miles and the check engine light has not come on again.

If you have a CEL Code 71, do the following steps:

1. This step takes only a minute to do. With the car idling, connect a vacuum line to the port on top of the EGR valve. 1 of the 3 ports on top of the throttle body is a good source to use as a vacuum line. If the engine hesitates or dies immediately, your EGR valve is good. If it is not affected, your egr valve is bad.

2. Remove the EGR Vacuum Modulator valve and soak it in a glass of Sea Foam to loosen the carbon. See above.

3. Ohm out the EGR gas temp sensor. With my engine at operating temperature the resistance was constant at 42.5K ohms.

4. It certainly wouldn’t hurt to remove the EGR valve and the half inch plate that it is bolted to, and clean that plate. I did, and found it was caked a half inch thick with carbon buildup due to the metal gasket being between that plate and the EGR valve. Also, the EGR temp sensor is screwed into the bottom of that plate and there was plenty of carbon buildup around it too.

From my experience in finding this repair, your problem is most likely going to be that the EGR Vacuum Modulator is plugged up with carbon. Simply cleaning or replacing the EGR Vacuum Modulator should fix your Code 71 problem.

Don’t forget to clear the CEL light by pulling the EFI fuse.

 

I've tried cleaning my EGR vacuum modulator as described above. No success for me as the CEL comes back shortly after reset.

Has the Code 71 come up for you since this post?

 

The cel came back on 1 mile after I posted that fix. I was pretty PO'd. I replaced the EGR vacuum modulator which fixed the problem.

I sold the '92 Lexus LS400 in December 06 and immediately purchased a 2000 Lexus LS 400. What a sweet ride. No problems either!

 

Cleaned my EGR modulator assy using spray carb cleaner, and fixed CEL code 71. 92 LS400.

 

How bizarre... on my LS400, the CEL didnt start coming on until I had the throttle body cleaned. What gives?

 

The gunk might have come off and lodged into your EGR valve. Take it off, give it a cleaning, and it will operate fine again. Pretty easy to do as well, and you can check all points for leaking vacuum as I stated in the other post.

 

Did that... actually took it to a shop and paid them $56 to clean the EGR system... 85 miles later, the CEL came back on... still showing code 71.

 

I chased a code 71 around a while. The EGR temp sensor looked fouled, so I replaced it with an aftermarket and that didn't do it. Should have started here first, but pulled out the EGR Vacuum Modulator. Popped the top off, filter was hard and dirty, and the guts had some carbon buildup. Replaced the filter with some universal filter fabric, used MAF sensor cleaner on the unit and then blew compressed air through every orifice. Dialed it back in, no problem since. Lesson is if you are throwing code 71 and your EGR passes the vacuum line test, pull and clean out your vacuum modulator. It's easy to pull and takes about 15 mins tops.