'97 Camry - Check Engine code P0401 - Insufficient EGR Flow

Hi guys, I just got a Check Engine light on yesterday. I went to Autozone and got an OBD-II Trouble Code: P0401, Insufficient EGR Flow Insufficient. The Autozone guy showed me an EGR valve for $164 and said it maybe blocked or something. I also checked with a friend who says that as long as the engine is not overheating it should be okay for driving for now.

So the far the car runs just fine, I haven't experienced any issues out of normal. I don't know much about this one, can anyone help? Does the code mean the value need to be replaced? And is this something for my shade-tree mechanic friend to help do, or something I should really give it to a pro to do? Thanks lots.

See the following post in the FAQ thread at the top of this forum:
http://www.automotiveforums.com/vbulletin/showpost.php?p=3203705&postcount=21

Thanks for the info, I'll clean out the carbon out of the EGR valve area. Does anyone know how to get to the EGR valve? Descriptions, diagrams/photo would be great. Thanks in advance!

Anytime you ask for assistance, please provide the engine designation and car year (done) with your question.

4 Cylinder EGR valve is on top rear of engine behind intake plenum. From front of car, left gadget is EGR vacuum modulator. Right gadget is EGR valve - has one nipple coming out the top.

6 cylinder EGR is on top of engine to right of intake plenum. Has electical connector in front.

FWIW, I just went through this with a 97 4 cyl. In my case it was the VSV, which seems to be the most common hardware failure of the 3 major EGR pieces (EGR Valve, Vacuum Modulator, and VSV).

I ask for troubleshooting and testing advice.

What have I missed?

I have got a P0401 "EGR flow insufficient"message on my Daughter's 97 Camry LE 4 cylinder automatic trans California emissions car with 198,000 miles.

The Daughter brought me the car with Check engine light on. She says a mechanic at her college town says the car has an EGR trouble code and the car probably needs a real hard to get at electric valve under the car replaced.

First test: Apply hand vacuum pump to EGR valve and observe engine stumble and die with about 50 mm Hg vacuum.

Clean egr valve and inspect feed pipe. The 1/2" diameter exhaust pipe tube has a little dry soot. Tape up intake manifold hole, start engine and observe vigorous puffs of exhaust.

The pressure tube from the EGR valve to EGR regulator is a bit crusty. I replace it. Put EGR valve back.

Clear the trouble codes by replacing the battery. A road test shows check engine light again. I buy an OBD-II reader and see P0401 Insufficient EGR Flow again.

Next, replace the EGR vacuum regulator because it seems dusty and tests show it only applies about 10mm Hg vacuum to the EGR valve diaphragm.
Use the hand vacuum pump to ensure all lines don't leak and the two tubes to the throttle body are clear and correctly connected. A road test with a old vacuum gage teed into the EGR valve vacuum hose shows the new EGR vacuum regulator also only applies about 10mm Hg vacuum to the EGR valve. The EGR vacuum switching valve under the car appears to be switching vacuum on and off at the times described in an online Toyota technical article.

Car is still throwing P0401 EGR Flow insufficient error code.

I am beginning to understand the OBD code reader data and I am puzzled by a .660 volt reading from the Oxygen sensor for Sensor 1 bank 1. So I replace the Oxygen sensor and the spark plugs. No change in Oxygen sensor voltage.
Car is still throwing P0401 EGR Flow insufficient error code.

Well there is not much else left to replace so I replace the VSV vacuum switching valve. I reconnect the tubing very carefully matching old and new tubing locations. The new VSV is a Dorman item showing 55 ohms where the old Toyota VSV showd 33 ohms.
Still throwing a P0401 code on a road test.

I read a Toyota article that this car tests the EGR gas flow by blipping the EGR gas flow on and watching for a pressure drop to show up on the MAP sensor.

I clean the MAP sensor connecting tube and manifold fitting. I hook up the MAP sensor to a hand vacuum pump and observe voltages on pin 2 of the sensor plug. Later I simply attach the OBD code reader and compare the OBD Live vacuum value reported with Key on and engine not running and compare that number with the dial reading on my hand vacuum pump.

As noted on this website, the Haynes manual has the MAP voltage and pressure values inverted. The vacuum in inches Hg showing on a hand vacuum pump (connected to the MAP sensor) added with the MAP sensor vacuum number showing on the OBDII code reader adds up to pretty near 29.5 inches Hg which is about the same as a maximum vacuum. Conclusion, the MAP sensor is OK.
Car still throws same EGR Flow insufficient error.

I have seen screwy things happen in the past when there is a bad ground connection. From the MAP sensor pin 3 (the sensor ground) I look for voltage drop over to the negative post of the battery and also for voltage drop at an engine ground lug near the timing belt. I see only .003 volts with key on, and only .008 volts with the headlights turned on. No major bad ground problems that I can see.

Well, something tells me I have a high mileage marginal car. What should I do next? Take apart the intake manifold (like Hondas need) or what?

Download the factory manual here (http://dc383.4shared.com/download/cRKgUsuH/1997-2001_Camry_Repair_Manual.zip?tsid=20131130-032145-450acdb8)

Test the EGR components as described in the emission_control.pdf file.

You can also go through the diagnostics in the Diagnostics.pdf file, but it sounds like you have done most of this already. Check it and see if you missed anything.

You have an A/F Ratio sensor at Bank 1 Sensor 1. I hope you confirmed that you bought the correct sensor by supplying a Toyota parts department with your VIN number to get the correct A/F Ratio sensor part number for your car. Calif and non-Calif cars are very different.

You have to measure the output voltage of the A/F Ratio sensor with a OBD-II tester or a Toyota hand-held tool. The voltage output of the sensor as measured by an OBDII tester is 1/5 the voltage measured by a Toyota hand-held tester.

After all is said and done, you may need to try a different ECM.

Sent to me by PM:

My daughter is using the car for a week, still with the EGR problem.

The last test was I attached a vacuum pump and gage with a Tee between the VSV vacuum switching valve and the EGR valve. On an extended road test I saw no vacuum at all meaning the VSV never opened.

I squeezed the vacuum pump which should have done nothing because the EGR valve is supposed to be vented to the atmosphere when the VSV is not energized. Suprise... the vacuum pump opened the EGR valve and caused the idling engine to die.

Hypothesis one is the VSV valve is installed reversed. I swapped the VSV hoses at the top of the engine and did another road test.
Result: Still I see no vacuum applied to the EGR valve. Manual pumping kills the engine at idle again.

I need more time to test further. Am I getting vacuum applied to the input of the VSV? That test will come next week.

I don't have a good set of test leads for looking at voltages applied to the VSV. The valve is buried too far under the engine.

Check engine light is Off and P0401 Insufficient EGR Flow trouble code is gone. I'll tell you the tests I worked out and the changes I made so you don't have to spend $600 on parts and tools and about 10 amateur mechanic days.

'97 Camrys with the 4 cylinder engine showing the P0401 Insufficient EGR Flow are typically fixed by replacing a VSV vacuum switching valve.

If your troubleshooting indicates you need a valve, I recommend you buy the Toyota dealer replacement valve because the Dorman part has a different bracket.

I did the Haynes and Toyota manual troubleshooting steps and replaced the VSV (it was bad). The valve is under the car and you can not see the tube connections. The VSV has two vacuum tubing connections called E and G. E goes up to the EGR valve and G goes up to the EGR regulator.

I pinched the E tube when installing the aftermarket valve. Somebody else had replaced the EGR vacuum tubing before me and the tubing was a tiny bit short. But I did not understand that the VSV valve works the opposite of the way I thought it works. When troubleshooting with a hand held vacuum pump, the pinched hose looks just like the E and G hoses are reversed.

The Haynes 97-2001 Camry manual page 6-26 step 11d says: "Blow air into the port nearest the filter port E and verify it flows out the port nearest the electrical connector Port G." That means, when the power is off, vacuum can pass from the regulator to the EGR valve.

Here is a big change not clear: The port Q on the vacuum regulator connects to port G on the vacuum switching valve. The other side of the vacuum switching valve, port E connects to the EGR valve. See? The switching valve stops the EGR system when the computer sends electricity through the vacuum switching valve.

When the vacuum switching valve is off (no electricity) the G hose to the EGR regulator is open through to the E hose to the EGR valve. The vacuum path is on or open when the valve is off.

When the vacuum switching valve is on (electricity on) the G hose to the regulator is shut. The E hose from the EGR valve is switched to a filter which is part of the switching valve.

The EGR valve plumbing has .157" diameter fittings and I think 5/32" vacuum hose is the nearest inch dimension.

You may have to buy a long tube and fittings to do the following tests:

With the car stopped and engine off, pull the Q hose off of the EGR vacuum regulator and attach a hand operated mechanics vacuum pump. Pull the single hose off the EGR valve and plug the end with your finger. Operate the hand pump and see vacuum. Remove finger and see no further vacuum. This tests if the vacuum tubing and VSV are hooked up. If you have a pinched hose, this should reveal it.

Here is how to road test the EGR system. With a tee and tubing attach a vacuum gauge to the EGR valve. Drive the car until the coolant is over 140 degrees F. When the computer sees the coolant is over 140, then it de-energizes the VSV and you will see vacuum applied to the EGR valve when the engine is at moderate load at highway speed. If the engine is cold or other conditions apply, the computer shuts off the EGR valve by energizing the VSV. I used a OBD-II code reader to watch engine temperature for the test.

When I installed the replacement VSV valve, I tried to exactly match the original Toyota installation. The factory location is extremely difficult to reach and the connections were all not visible. I don't recommend changing a car away from the factory setup. Unfortunately, the Dorman replacement VSV is inappropriate at the original location. Looking further under the car, moving 6 inches toward the centerline of the vehicle, there is an intake manifold strut and the vacuum hoses and electrical harness are easily visible. First I made a 1" tubing sleeve and secured the VSV with a cable tie to the manifold strut. Two more cable ties hold the VSV against sliding. The electrical and tubing connections are all visible and not folded or rubbing.

For the curious, how did I spend $600? ObdII tester $70, Manual $30, replace regulator, $80, replace California AF sensor $280 (confused by voltage values reported, they are OK), replace flexible engine exhaust pipe section $130, battery $110, spark plugs $40.

Download the factory manual here (http://dc383.4shared.com/download/cRKgUsuH/1997-2001_Camry_Repair_Manual.zip?tsid=20131130-032145-450acdb8):



Downloading the manual from this site requires installing malware on my computer using a file down loader named iLividSetup-r1236-n-bf.exe

Downloading the manual from this site requires installing malware on my computer using a file down loader named iLividSetup-r1236-n-bf.exe

No it doesn't. You are not clicking on the correct link.

Click on the "Download" link immediately under and to the left margin of the area stating: "1997-2001 Camry Repair Manual - download at 4shared. 1997-2001 Camry Repair Manual is hosted at free file sharing service 4shared." Then click on "Free Download". You may have to register with 4shared.

No it doesn't. You are not clicking on the correct link.

Click on the "Download" link immediately under and to the left margin of the area stating: "1997-2001 Camry Repair Manual - download at 4shared. 1997-2001 Camry Repair Manual is hosted at free file sharing service 4shared." Then click on "Free Download". You may have to register with 4shared.

Thank You for helping me navigate a tricky website. One wrong click and they own your computer.

Sorry, it's difficult to find a good and free file sharing site. 4shared reacts differently to me as a registered user, than to unregistered downloaders.

Hi, I have a 97'Camry (4Cyl) with 130K+ miles on it and recently had the oil changed along with engine and fuel system cleaning as it was recommended by the service technician. And about a day after, the check engine light came on and when I went back, the technician told the code was P0401 and had something to do with the EGR system.

I am wondering if the P0401 code had something to do with the special oil change. Is that a possibility?

Here are the special things done over and above the conventional oil change -


Install internal engine cleaner to remove harmful crankcase contaminants and ensure optimum oil circulation
Install turbo approved oil treatment to reduce friction and enhance oil pumpability to maximize protection
Install fuel system cleaner to remove moisture, clean injectors and intake valves and lubricate upper cylinder area

Thank you

Answering Mr. ajasras. My 40 years of experience is any sudden new problem that shows up after I worked on my car is usually caused by something I did. I call it Lee's first law of mechanics.

Contact the mechanic that did your extended special oil change and ask him to look at the EGR tubing connections for a pulled, pinched or swapped hose.

Since your Camry is 17 years old, a previous mechanic many years ago may have replaced the original metric dimension Toyota hose with an inch dimension hose that doesn't fit quite as tight. The EGR system vacuum switching valve VSV is behind the engine and way down. It is very hard to see and I found it hard to reach.

So, check for something pulled loose. Cheap and easy fix we hope huh?

Thank you lmckusic.

I did check with the mechanic and he wanted me to leave the vehicle for a day so that he can run some tests on it. In the meantime, I will check the EGR system myself for any loose hoses and try to follow the recommended solutions from this awesome forum.

Will report back what I find. Thanks