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Old 08-09-2011, 10:58 AM   #1
NEHOG
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Default 97 Accord 4 P1491 code

Didn't find much on a search for P1491... So:

Was getting an insufficient egr flow DTC, so I cleaned the ports in the intake (all were totally 'crudded' up). Now I'm getting a P1491 code (which I didn't get before...)

The diagnostics say I should have about 8" of vacuum at the EGR valve, but I'm reading about 6... Took the vacuum control valve off (left had fender) and checked both the valve and the vacuum regulator on the bench (nice to have a bench vacuum supply!) and it appears the regulator is limiting it to 6" of vacuum. I think this may be why the insufficient lift code is set, but, my Honda experience is rather limited. (checked for vacuum leaks, none present.)

Two questions...

Could the regulator be simply taken out for a test? We need to get this past emissions testing and the son-in-law doesn't have a lot of money for test parts... If in fact it stops setting the code then we could spring for a new regulator.

Second question is more generic--any other thoughts on this? The EGR valve itself is cleaned as are the ports, no blockages. One problem this car had was the coolant hose to the throttle body was leaking and did spray the EGR valve area some. Could possibly the EGR valve's sensor (on top of the valve) have been damaged by coolant? (I suspect not, but figured I'd ask.)

BTW, car has about 200K miles on it, but is in generally good condition. I just put in a new radiator, headlight assembly and exhaust (cat back).
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Old 08-11-2011, 04:00 AM   #2
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Default Re: 97 Accord 4 P1491 code

I'm a bit surprised, simple question and not even one reply...
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Old 08-14-2011, 12:32 PM   #3
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Default Re: 97 Accord 4 P1491 code

One of the things that makes a forum such as this is having people who are at least willing to try to answer a question. Now, before you jump on my butt and say "He's a newbee" or whatever, realize that I am a resident expert (with 14K posts to my credit) on another (non Honda) forum.

I'll say two things:

1. It appears to me that no one around here cares to try to assist. So what is the purpose for this forum? Did I misunderstand its reason? Is it for bling? Modifications only? Am I wrong to be puzzled as to the total lack of response (basically being ignored)?

2. I don't see a good future for this place if you 'welcome' others the way I have been welcomed. I did my homework, I did a search, got nothing. Asked a question and got zip.

I'll check back once more in a few days... Not for an answer to my original question however. That I'm fixing with the time honored 'just replace everything' since I want this thing fixed and I'm tired of messing with it. Instead I'll check back and see if any can do a decent job of flaming me. Go ahead, call me an intruding jerk if you want. Or better yet, just ignore me.

I apologize for bothering you good folks.
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Old 08-14-2011, 12:44 PM   #4
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Default Re: 97 Accord 4 P1491 code

Quote:
Originally Posted by NEHOG View Post
One of the things that makes a forum such as this is having people who are at least willing to try to answer a question. Now, before you jump on my butt and say "He's a newbee" or whatever, realize that I am a resident expert (with 14K posts to my credit) on another (non Honda) forum.

I'll say two things:

1. It appears to me that no one around here cares to try to assist. So what is the purpose for this forum? Did I misunderstand its reason? Is it for bling? Modifications only? Am I wrong to be puzzled as to the total lack of response (basically being ignored)?

2. I don't see a good future for this place if you 'welcome' others the way I have been welcomed. I did my homework, I did a search, got nothing. Asked a question and got zip.

I'll check back once more in a few days... Not for an answer to my original question however. That I'm fixing with the time honored 'just replace everything' since I want this thing fixed and I'm tired of messing with it. Instead I'll check back and see if any can do a decent job of flaming me. Go ahead, call me an intruding jerk if you want. Or better yet, just ignore me.

I apologize for bothering you good folks.

You are really anxious,man!.Not everybody stuck to the computers all day long!
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Old 08-14-2011, 01:00 PM   #5
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Default Re: 97 Accord 4 P1491 code

Quote:
Originally Posted by NEHOG View Post
Didn't find much on a search for P1491... So:

Was getting an insufficient egr flow DTC, so I cleaned the ports in the intake (all were totally 'crudded' up). Now I'm getting a P1491 code (which I didn't get before...)

The diagnostics say I should have about 8" of vacuum at the EGR valve, but I'm reading about 6... Took the vacuum control valve off (left had fender) and checked both the valve and the vacuum regulator on the bench (nice to have a bench vacuum supply!) and it appears the regulator is limiting it to 6" of vacuum. I think this may be why the insufficient lift code is set, but, my Honda experience is rather limited. (checked for vacuum leaks, none present.)

Two questions...

Could the regulator be simply taken out for a test? We need to get this past emissions testing and the son-in-law doesn't have a lot of money for test parts... If in fact it stops setting the code then we could spring for a new regulator.

Second question is more generic--any other thoughts on this? The EGR valve itself is cleaned as are the ports, no blockages. One problem this car had was the coolant hose to the throttle body was leaking and did spray the EGR valve area some. Could possibly the EGR valve's sensor (on top of the valve) have been damaged by coolant? (I suspect not, but figured I'd ask.)

BTW, car has about 200K miles on it, but is in generally good condition. I just put in a new radiator, headlight assembly and exhaust (cat back).
You can test the valve on the car.It's a quick test.You need the vacuum pump .While the engine idling apply the vacuum slowly-the car should die.
Another thing you could check is the control solenoid which alowing the vacuum to the EGR when the conditions are met.The valve is a solenoid.The quick test for it is to unplug it and power it up with 12Volts.You should hear a click and you should be able to blow the air trough,and the opposite, when power is off the air shouldn't be able to go through.Next ,the sensor on the top of the valve is nothing more than a potentiometer and it tells the ECU the position of the valve lift.It can be checked with the help of the scanner(not easy without the tool).
Next,you could check the wiring between the EGR valve and ECU.(if I'm not mistaking the re should be power in one of them with the key on and another is being grounded by ECU).check the integrity of both.
And the last thing.If after everything being tested is within the specs then is the ECU making troubles.But do the tests before!
There you go,man!Now you will have less time to complain about forum members
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Old 08-15-2011, 09:04 AM   #6
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Default Re: 97 Accord 4 P1491 code

Quote:
Originally Posted by exb18c1 View Post
You can test the valve on the car.It's a quick test.You need the vacuum pump .While the engine idling apply the vacuum slowly-the car should die.
Another thing you could check is the control solenoid which allowing the vacuum to the EGR when the conditions are met.The valve is a solenoid.
yes, I'm familiar with that valve. Driver's side fender.
Quote:

The quick test for it is to unplug it and power it up with 12Volts.You should hear a click and you should be able to blow the air trough,and the opposite, when power is off the air shouldn't be able to go through.
A slightly better test is to put a vacuum gauge on the hose at teh EGR valve and measure vacuum with the engine running. (hint: specs are about 18-20 inches going into the vacuum valve/regulator, and 8 inches vacuum at the EGR valve.)
Quote:


Next ,the sensor on the top of the valve is nothing more than a potentiometer and it tells the ECU the position of the valve lift.It can be checked with the help of the scanner(not easy without the tool).
That's a bit of information that I was looking for. I suspected it was a potentiometer but wasn't sure. That would let me test it (the EGR valve) a bit more.
Quote:

Next,you could check the wiring between the EGR valve and ECU.(if I'm not mistaking the re should be power in one of them with the key on and another is being grounded by ECU).
You're correct, 12V is there with key on, and the ECM does ground the other pin to turn it on. (Yes, I've the requisite 12 volts so that is good, I'll check the wire to the ECM.)
Quote:
check the integrity of both.
And the last thing.If after everything being tested is within the specs then is the ECU making troubles.But do the tests before!
There you go,man!Now you will have less time to complain about forum members
Notice the 8 inches of vacuum at the EGR valve? Oops, I'm reading only six. I may well have a problem there. That plastic green and white device with the vacuum valve is a regulator, and it appears it is not quite working correctly. I've ordered one and will test that again. And I'll check the wire to the ECM, but I think it is probably OK.

Now, I'm pleased that someone answered me! Not only that but your answer was excellent and gave me a bit of information I didn't have already (how the sensor in the EGR valve works...)

For that I thank you...

(For exb18c1, no original question was posted on 8/9, and I screamed on 8/14, five days later! (odd, smilies are not working for me today?) ;-} )
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Old 08-15-2011, 09:24 AM   #7
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Default Re: 97 Accord 4 P1491 code

Quote:
Originally Posted by NEHOG View Post
yes, I'm familiar with that valve. Driver's side fender. A slightly better test is to put a vacuum gauge on the hose at teh EGR valve and measure vacuum with the engine running. (hint: specs are about 18-20 inches going into the vacuum valve/regulator, and 8 inches vacuum at the EGR valve.) That's a bit of information that I was looking for. I suspected it was a potentiometer but wasn't sure. That would let me test it (the EGR valve) a bit more. You're correct, 12V is there with key on, and the ECM does ground the other pin to turn it on. (Yes, I've the requisite 12 volts so that is good, I'll check the wire to the ECM.)

Notice the 8 inches of vacuum at the EGR valve? Oops, I'm reading only six. I may well have a problem there. That plastic green and white device with the vacuum valve is a regulator, and it appears it is not quite working correctly. I've ordered one and will test that again. And I'll check the wire to the ECM, but I think it is probably OK.

Now, I'm pleased that someone answered me! Not only that but your answer was excellent and gave me a bit of information I didn't have already (how the sensor in the EGR valve works...)

For that I thank you...

(For exb18c1, no original question was posted on 8/9, and I screamed on 8/14, five days later! (odd, smilies are not working for me today?) ;-} )
Did you check the vacuum at the valve with the engine fully warm?Too bad I don't have the system in front of me.Is there another valve between the EGR and EGR 's soleniod?
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Old 08-15-2011, 09:39 AM   #8
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Default Re: 97 Accord 4 P1491 code

Can you kill the motor by applying the the vacuum directly to the EGR valve?
You can also check if the EGR's diafragm sealing properly by applying the vacuum to the port and check if it holds the vacuum.It's not obvious when you clean EGR if it really worked.Lets say that computer commanded the vacuum to pull the pintle open,but because of deposits the pintle did't open up all the way.The ECU (via the potentiometer)will not see that the lift achieved and will assume that there is not enough flow.
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Old 09-04-2011, 03:29 PM   #9
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Default Re: 97 Accord 4 P1491 code

Final followup... Replaced EGR valve, the solenoid, and the vacuum regulator. I got a good deal on the solenoid and regulator (used), the EGR I got new.

I bench tested the solenoid and regulator, and got a higher vacuum reading than the original gave me (original was six inches, the replacement was about eight (the specified amount) which was good. Because I needed to get this working right for an emissions inspection, I did the EGR valve as well.

Its been three weeks or so since I finished the repairs, the CE light is still off, it has passed inspection, and all is well.

For the history records--I believe the problem was insufficient vacuum from the regulator, however I didn't have the time to diagnose it any further.
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01, 1997, 97, accord, code, codes, ecm, egr, honda, key, leak, p1491, test, vacuum, wiring

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