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94 Es300 Check Engine Light - P0401

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Hi Guys,

The code P0401 indicates EGR. Are there any more I can check before I replace the EGR. It cost $175.00 @ Autozone and it is hard to install. Any help will do. Thanks.

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Do not replace the egr valve without further testing, chances are that is not the problem. You need to check the vac modulator before replacing the egr valve. Do you have a manual? It would also be a worthwhile to purchase a hand held vac pump, harbor freight sells one for about $20 or so. The quick easy way to check the valve and passageways is to use the handheld pump to apply vaccum to valve while the engine idles. If the valve is working, the engine will start running extremely rough. While the engine is off, you can apply vaccum to the valve and see if it hold a vac for awhile. If it holds a vac, the diapham inside the valve is good. With these two test you will know if there is any problem with the valve and the egr tubes.

Anyway, the issue is probably the modulator, or the egr sensor.

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Do not replace the egr valve without further testing, chances are that is not the problem. You need to check the vac modulator before replacing the egr valve. Do you have a manual? It would also be a worthwhile to purchase a hand held vac pump, harbor freight sells one for about $20 or so. The quick easy way to check the valve and passageways is to use the handheld pump to apply vaccum to valve while the engine idles. If the valve is working, the engine will start running extremely rough. While the engine is off, you can apply vaccum to the valve and see if it hold a vac for awhile. If it holds a vac, the diapham inside the valve is good. With these two test you will know if there is any problem with the valve and the egr tubes.

Anyway, the issue is probably the modulator, or the egr sensor.

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Do not replace the egr valve without further testing, chances are that is not the problem. You need to check the vac modulator before replacing the egr valve. Do you have a manual? It would also be a worthwhile to purchase a hand held vac pump, harbor freight sells one for about $20 or so. The quick easy way to check the valve and passageways is to use the handheld pump to apply vaccum to valve while the engine idles. If the valve is working, the engine will start running extremely rough. While the engine is off, you can apply vaccum to the valve and see if it hold a vac for awhile. If it holds a vac, the diapham inside the valve is good. With these two test you will know if there is any problem with the valve and the egr tubes.

Anyway, the issue is probably the modulator, or the egr sensor.

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Thanks for your input George. I see the vacuum modulator but I don't see a sensor. I guess 1994 does not have an EGR sensor. Is there any way to clean the modulator or I just have to buy a new one. Anyway, thanks again. I hope the CEL will disappear after this.

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There is a egr temp sensor, this is what the ECM uses to determine egr flow. I can send you a word doc that describes how to check the egr modulator, send me a PM with your email (I cannot upload word docs to this site).

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Hi Guys,

The code P0401 indicates EGR. Are there any more I can check before I replace the EGR. It cost $175.00 @ Autozone and it is hard to install. Any help will do. Thanks.

Has the same check engine code on my 95 ES300. As George pointed out, in all probability it's the vac modulator. EGR valve failure is very uncommon and nearly everyone who has posted here has fixed the P0401 CEL by replacing the vac modulator (myself included).

The diaphragm's in the modulator dry rot and no longer hold a vacuum, causing the CEL. Dealer wants like $70+ for one, picked up a aftermarket one off Ebay for $29 shipped to my door. Works like a champ, no more CEL!

Here's the seller....

Ebay Aftermarket Vacuum Modulator

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Hi Guys,

The code P0401 indicates EGR. Are there any more I can check before I replace the EGR. It cost $175.00 @ Autozone and it is hard to install. Any help will do. Thanks.

Has the same check engine code on my 95 ES300. As George pointed out, in all probability it's the vac modulator. EGR valve failure is very uncommon and nearly everyone who has posted here has fixed the P0401 CEL by replacing the vac modulator (myself included).

The diaphragm's in the modulator dry rot and no longer hold a vacuum, causing the CEL. Dealer wants like $70+ for one, picked up a aftermarket one off Ebay for $29 shipped to my door. Works like a champ, no more CEL!

Here's the seller....

Ebay Aftermarket Vacuum Modulator

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Hi Guys,

The code P0401 indicates EGR. Are there any more I can check before I replace the EGR. It cost $175.00 @ Autozone and it is hard to install. Any help will do. Thanks.

Has the same check engine code on my 95 ES300. As George pointed out, in all probability it's the vac modulator. EGR valve failure is very uncommon and nearly everyone who has posted here has fixed the P0401 CEL by replacing the vac modulator (myself included).

The diaphragm's in the modulator dry rot and no longer hold a vacuum, causing the CEL. Dealer wants like $70+ for one, picked up a aftermarket one off Ebay for $29 shipped to my door. Works like a champ, no more CEL!

Here's the seller....

Ebay Aftermarket Vacuum Modulator

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I just replace the modulator for my 94 es300. The CEL is still on. What is next? Where is the EGR sensor on this car. Alldata diagram is only showing vacuum modulator, egr valve & vacuum switching valve. Hope to hear from you guys.

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Hi, I actually work at a toyota dealer and deal with this fault every once in a while on your 1mz-fe engine. First thing to check is to see if you have egr flow with the engine running. Start the car and let it warm up. Disconnect the vacuum line from your egr valve and hook a vaccuum line connected to a vacuum pump to the egr valve and apply vacuum to the egr valve. The car should stall or run very rough due to an extreme lean condition caused by the valve being opened and causing exhaust flow into the plenum. If there is very little change in the way the car runs with vacuum applied to the egr valve then the passage is clogged with carbon and restricting egr flow. If this is the case then you need to remove the egr valve, remove the air intake tube from the throttle body, hold the throttle open with one hand, and then try spraying throttle body cleaner into the passage between the egr valve and plenum. As you spray throttle body cleaner through the passage you should see a steady stream going into the plenum. If it is clogged you will not see anything entering the plenum or there will be very little cleaner getting into the plenum. This passage normally clogs up with high mileage vehicles. If it is clogged then use a straight piece of metal to clean out the passage. I get a metal coat hanger and cut a good 6 inch straight piece of metal off of one and then just shove it into the passage and ream the passage out until it is cleaned and i can spray cleaner through the passage and see it coming out as a steady stream through the plenum. If the vacuum test works, and the car dies or runs extremely rough then i usually recommend the egr vacuum modulator and egr vacuum switching valve. The switching valve is located under that decorative plastic cover on the top of the engine. It is an electrical part and can start to work intermittently and cause the this problem as well. This electrical valve will cause vacuum not to get to the egr valve and hence cause no egr valve flow. You will see the vacuum lines coming from the modulator to the valve and then to the egr valve. Hope this helps. I have to admit that I have not seen an egr temp sensor go bad yet.

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Hi Guys,

The code P0401 indicates EGR. Are there any more I can check before I replace the EGR. It cost $175.00 @ Autozone and it is hard to install. Any help will do. Thanks.

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Thank you all guys for replying to this thread. I guess I posted too quickly that the CEL is still ON when I replaced the vacuum modulator. After my wife drove the car for a few days, the CEL disappeared. My guess is that you have to drive the car for a few miles after changing the modulator for the CEL to reset. I am just guessing I don't know if that is true. Anyway my problem is solved. All your responses to this thread are excellent. More power to you guys.

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Hi, I actually work at a toyota dealer and deal with this fault every once in a while on your 1mz-fe engine. First thing to check is to see if you have egr flow with the engine running. Start the car and let it warm up. Disconnect the vacuum line from your egr valve and hook a vaccuum line connected to a vacuum pump to the egr valve and apply vacuum to the egr valve. The car should stall or run very rough due to an extreme lean condition caused by the valve being opened and causing exhaust flow into the plenum. If there is very little change in the way the car runs with vacuum applied to the egr valve then the passage is clogged with carbon and restricting egr flow. If this is the case then you need to remove the egr valve, remove the air intake tube from the throttle body, hold the throttle open with one hand, and then try spraying throttle body cleaner into the passage between the egr valve and plenum. As you spray throttle body cleaner through the passage you should see a steady stream going into the plenum. If it is clogged you will not see anything entering the plenum or there will be very little cleaner getting into the plenum. This passage normally clogs up with high mileage vehicles. If it is clogged then use a straight piece of metal to clean out the passage. I get a metal coat hanger and cut a good 6 inch straight piece of metal off of one and then just shove it into the passage and ream the passage out until it is cleaned and i can spray cleaner through the passage and see it coming out as a steady stream through the plenum. If the vacuum test works, and the car dies or runs extremely rough then i usually recommend the egr vacuum modulator and egr vacuum switching valve. The switching valve is located under that decorative plastic cover on the top of the engine. It is an electrical part and can start to work intermittently and cause the this problem as well. This electrical valve will cause vacuum not to get to the egr valve and hence cause no egr valve flow. You will see the vacuum lines coming from the modulator to the valve and then to the egr valve. Hope this helps. I have to admit that I have not seen an egr temp sensor go bad yet.

hi I found this post very interesting I've done most of the test and replaced modulator paid $78,99 at Hub Auto in costa mesa ca

but the code still there and following your reconmendation I need to purchase the egr vacuum switching valve any idea how much is it and if it is a dealer item only

thanks Frank Leopo

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