Again P0401 Egr Valve

[ibuddler]

I had this code months ago and I read the thread and replaced the EGR sensor. After replacing the sensor (1 day after) the code came again. So I'm wondering what should I do now. The car idle is just fine! Do I have to replace the valve? I took the valve out before and cleaned it.

Any suggestions?

[ibuddler]

I had this code months ago and I read the thread and replaced the EGR sensor. After replacing the sensor (1 day after) the code came again. So I'm wondering what should I do now. The car idle is just fine! Do I have to replace the valve? I took the valve out before and cleaned it.

Any suggestions?

I clean up the code and it came on again with the same code. But I didn't feel I'm losing power. Will it be anything else other than EGR?

[spalkin]

I had this same problem.

P0401 is EGR Insufficient Flow. The EGR system knows if flow is coming through by a little temp sensor right in the throttle body by the inlet from the exhaust.

If the sensor doesn't get hot, it knows there's no flow because if there was, it would definitely get hot.

Now we know exactly how the computer picks up a code P0401.

This could be caused by one or more of several things (that's what makes this such a tough one)

First, it could be that the EGR valve is stuck or not getting good vacuum - easy to test

Second, it could be because the vacuum modulator on the EGR valve Assembly is clogged and not letting the EGR open - easy to test

Third, it could be the EGR's vacuum switch isn't getting vacuum or is stuck - not uncommon but it's probably OK - easy to test

Fourth, it could be that the EGR piping that comes up from the exhaust is clogged a bit with deposits and isn't letting the gasses come up - Not easy to test, and if it is, then you'll be changing all kinds of parts to find the fix and you'll clear the code and a week later it'll show up again.

Yea, I had this very same problem. What cured it? A little spirited driving. Get that exhaust real hot. Accelerate hard and long. A great way to do this is by being late for a very important appointment. The light went out and I cleared the code and it's not been back.

You can clear that piping if you dismantle the pipe that goes down to the EGR Cooler on the back of the engine, also the pipe that goes from the EGR Cooler to the exhaust and cleaning with a cheap gun kit. Do not spray anything down that pipe! It could foul a very expensive sensor downline.

Hope this helps in some way. Cheers!

[ibuddler]

I had this same problem.

P0401 is EGR Insufficient Flow. The EGR system knows if flow is coming through by a little temp sensor right in the throttle body by the inlet from the exhaust.

If the sensor doesn't get hot, it knows there's no flow because if there was, it would definitely get hot.

Now we know exactly how the computer picks up a code P0401.

This could be caused by one or more of several things (that's what makes this such a tough one)

First, it could be that the EGR valve is stuck or not getting good vacuum - easy to test

Second, it could be because the vacuum modulator on the EGR valve Assembly is clogged and not letting the EGR open - easy to test

Third, it could be the EGR's vacuum switch isn't getting vacuum or is stuck - not uncommon but it's probably OK - easy to test

Fourth, it could be that the EGR piping that comes up from the exhaust is clogged a bit with deposits and isn't letting the gasses come up - Not easy to test, and if it is, then you'll be changing all kinds of parts to find the fix and you'll clear the code and a week later it'll show up again.

Yea, I had this very same problem. What cured it? A little spirited driving. Get that exhaust real hot. Accelerate hard and long. A great way to do this is by being late for a very important appointment. The light went out and I cleared the code and it's not been back.

You can clear that piping if you dismantle the pipe that goes down to the EGR Cooler on the back of the engine, also the pipe that goes from the EGR Cooler to the exhaust and cleaning with a cheap gun kit. Do not spray anything down that pipe! It could foul a very expensive sensor downline.

Hope this helps in some way. Cheers!

Thank you for you information. So you suggest to drive hard for a long time and the light will be off? Btw, where's the EGR Temp Sensor? I can't find it from FSM. Thanks.

[spalkin]

The temp sensor is just under the front of the throttle body throat.

I drive it gently all the time so it never gets blown out.

On mine, I tested all the pieces and they all were good. I didn't know what to do besides try to clear the tubing. Then, one day after some harder driving the light went out. The code was still stored though. I cleared the code and haven't seen it again.

Like I said, the components all tested good. That's all real good quality stuff. The exhaust gas temp sensor, usually never goes. The vacuum switch can go bad but usually lasts and lasts. It's a very simple part. The EGR valve itself is very dependable and doesn't take too much abuse since the EGR Cooler cools the gases coming into it. Those gases are hotter than hell, believe me. Mine was pretty clean, too. Even after 218,000 miles. It had to be the piping coming off the A Pipe. That pipe never needs changing so it's on there the whole life of the car. It gets full of deposits over a long period of time. When you need a new exhaust, they just change out everything behind the CAT. Everything in front of it gets so hot that water can't condensate in it. It stays perfectly solid. So, it gets full of deposits and can cover the little exit that sprigs off to feed the EGR system.

It worked for me. Also, use some Carb and Throttle Body Cleaner and some paper towels and really clean the throttle body opening. You won't believe how filthy that is. Dirty, oily gases from the crank case get sucked right into the front of the throttle body. That's called the Breather, and there's no filter on it.

Good luck!

[ibuddler]

The temp sensor is just under the front of the throttle body throat.

I drive it gently all the time so it never gets blown out.

On mine, I tested all the pieces and they all were good. I didn't know what to do besides try to clear the tubing. Then, one day after some harder driving the light went out. The code was still stored though. I cleared the code and haven't seen it again.

Like I said, the components all tested good. That's all real good quality stuff. The exhaust gas temp sensor, usually never goes. The vacuum switch can go bad but usually lasts and lasts. It's a very simple part. The EGR valve itself is very dependable and doesn't take too much abuse since the EGR Cooler cools the gases coming into it. Those gases are hotter than hell, believe me. Mine was pretty clean, too. Even after 218,000 miles. It had to be the piping coming off the A Pipe. That pipe never needs changing so it's on there the whole life of the car. It gets full of deposits over a long period of time. When you need a new exhaust, they just change out everything behind the CAT. Everything in front of it gets so hot that water can't condensate in it. It stays perfectly solid. So, it gets full of deposits and can cover the little exit that sprigs off to feed the EGR system.

It worked for me. Also, use some Carb and Throttle Body Cleaner and some paper towels and really clean the throttle body opening. You won't believe how filthy that is. Dirty, oily gases from the crank case get sucked right into the front of the throttle body. That's called the Breather, and there's no filter on it.

Good luck!

Hi, I've tried and that seems not work for me. But thank you anyway. My best guess is my O2 sensor was bad 1 year ago and I didn't pay attention to it for a year which results my EGR's damage.

[spalkin]

Oxygen Sensor not the problem. Test the components in the EGR system.

Remember, the one and only way the computer would store a P0401 Code is that Exhaust Gas Temp Sensor isn't sending the right temp value.

Now, why that sensor isn't sending the right temperature information is the tricky part.

Is the sensor just unplugged? That would definitely cause the computer to not see the right temp.

Are all the vacuum hoses related to the system intact and plugged into the right places? Should be.

We know the EGR valve itself is good now since you changed it out (you bonehead)

Is the vacuum switch for the EGR System working? If it wasn't, the EGR wouldn't open and that would cause a bad temp signal.

Is the tubing coming up from the exhaust clogged? If it was, the sensor wouldn't get hot.

Is the sensor itself working? If it was bad, it wouldn't send any temp info.

That's it, that's how you solve a check engine light. Often the toughest things to sort through because so many pieces upstream of a sensor go into it's reading.

There's a test, usually a very simple one, for every piece in the system. If you go through them all (like a good mechanic) nothing can get by you. You'll find out exactly what's wrong without spending a dime.

[N.C.O.]

Oxygen Sensor not the problem. Test the components in the EGR system.

Remember, the one and only way the computer would store a P0401 Code is that Exhaust Gas Temp Sensor isn't sending the right temp value.

Now, why that sensor isn't sending the right temperature information is the tricky part.

Is the sensor just unplugged? That would definitely cause the computer to not see the right temp.

Are all the vacuum hoses related to the system intact and plugged into the right places? Should be.

We know the EGR valve itself is good now since you changed it out (you bonehead)

Is the vacuum switch for the EGR System working? If it wasn't, the EGR wouldn't open and that would cause a bad temp signal.

Is the tubing coming up from the exhaust clogged? If it was, the sensor wouldn't get hot.

Is the sensor itself working? If it was bad, it wouldn't send any temp info.

That's it, that's how you solve a check engine light. Often the toughest things to sort through because so many pieces upstream of a sensor go into it's reading.

There's a test, usually a very simple one, for every piece in the system. If you go through them all (like a good mechanic) nothing can get by you. You'll find out exactly what's wrong without spending a dime.

What year is the ES? How many miles does it have? Have you check to see if the EGR valve is getting vacuum or not? When you clean the valve did you clean the passage too?

N.C.O.