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Old 08-09-2008, 12:34 PM   #1
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Default Code P1491 everything replaced still getting code

this is a 99 accord I4
egr valve is new, cat. is new, 1st o2 sensor is new.
what else could make it throw this code?
i don't see where i can get to egr ports to clean them. i am at a loss here.
thanks for any help.
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Old 08-09-2008, 02:23 PM   #2
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Default Re: Code P1491 everything replaced still getting code (tortis)

You will have to remove the intake manifold and clean out the ports. The main one from the head to the valve. Then take the maifold apart and clean out the second set of runners for the egr valve. There is alot of carbon that builds up in those 2 places. You may even need to drill out the main port some. Also clean out the port in the head.
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Old 08-09-2008, 05:13 PM   #3
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Default Re: Code P1491 everything replaced still getting code (Turbowa)

is there any preventive measures to keep this from happening again. seems like this is a repeating problem.
man i don't want to take this car apart days before a major road trip.
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Old 08-10-2008, 09:11 AM   #4
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Default Re: Code P1491 everything replaced still getting code (tortis)

all ports are clean. cleaned the connector that sits under the egr valve, and sprayed carb cleaner into the egr valve which was pretty clean.
i did find the clamp that connects the air intake to the throttle body a little looser than i like it. check engine light is off for now.
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Old 08-10-2008, 01:28 PM   #5
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Default Re: Code P1491 everything replaced still getting code (tortis)

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Old 08-10-2008, 03:27 PM   #6
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Default Re: Code P1491 everything replaced still getting code (Mr Yamada)

Thank You Mr. Yamada Sir. will take the TB off tomorrow and clean the that port.
thank you again.
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Old 08-10-2008, 03:28 PM   #7
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Default Re: Code P1491 everything replaced still getting code (tortis)

You will have to remove the intake manifold and clean out the ports. The main one from the head to the valve. Then take the maifold apart and clean out the second set of runners for the egr valve. There is alot of carbon that builds up in those 2 places. You may even need to drill out the main port some. Also clean out the port in the head.

with Mr. Yamada's pic i see what you are talking about. thank you.
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Old 08-11-2008, 10:22 AM   #8
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Default Re: Code P1491 everything replaced still getting code (tortis)


that area between the throttle body and intake was totally blocked. super thick black gunk. pine tar heroin thick. scraped and cleaned the bottom of the throttle body and cleaned the port in the intake manifold.


Modified by tortis at 2:59 PM 8/11/2008
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Old 08-11-2008, 11:25 AM   #9
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Default Re: Code P1491 everything replaced still getting code (tortis)

well turned off the CEL, drove it 15 minutes CEL back on. autozone checked it and P1491 pops up. i just undid the negative battery cable, instead of the fuse, hopefully it just didn't clear out.


Modified by tortis at 3:00 PM 8/11/2008
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Old 08-11-2008, 02:04 PM   #10
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Default Re: Code P1491 everything replaced still getting code (tortis)

alright, cel is on. P1491.

i am open to any ideas. i hate having my *** kicked when the opponent (the car) is trying to help. it has to be something simple.
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Old 09-12-2010, 03:04 PM   #11
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Default Re: Code P1491 everything replaced still getting code

I know this is an old post but I was wondering if you ever fixed your egr problem and if so how? I am in the same boat. Cleaned and replaced everything and I still get the P1491 code. Any thoughts anyone?
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Old 01-07-2011, 12:09 PM   #12
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Default Re: Code P1491 everything replaced still getting code

Same here. '98 Accord 2.3 4cyl VTEC. New EGR, New O2 sensor, Cleaned TB, upper IM. Removed tons of black gunk. Still throwing P1491.
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Old 01-10-2011, 10:12 AM   #13
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Default Re: Code P1491 everything replaced still getting code

Any Replies????
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Old 01-21-2012, 07:48 AM   #14
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Default Re: Code P1491 everything replaced still getting code

I too am in this boat. Could it be a battery voltage issue? Vestigial data in the computer's memory that only dealers can erase issue? After cleaning the carbon/tar out of the EGR valve & port/plenum (P0401 code) I had been starting the car by first putting the switch to the on position, waiting for all the bings and flashing lights to cease, then starting. I probably did this for a week each time, but then forgot and just started the car. Only after that did the CEL rear it's ugly head and before that a maintenance required light (unrelated?). Bad EGR?
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Old 01-21-2012, 12:41 PM   #15
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Default Re: Code P1491 everything replaced still getting code

If the passages are clear, and the EGR valve itself passes the vacuum tests, then you have to delve deeper.

The EGR control solenoid which is inside the control box on the firewall. On my year it is a kind of triangular shaped black box with hoses and wires attached to it. It's above the fuel filter and you have to unbolt the box to open it and get at the things inside it. That may differ on newer Accords.

There is a test for the EGR control solenoid to determine if its functioning properly, but too complicated to explain here. Of course, since this is emission systems stuff, it's not going to let us off easy, so to round things out, there is also a constant vacuum control (CVC) valve inside the control box that's also involved in monitoring and controlling exhaust gas recirculation. Speaking of that solenoid, I have actually parked my car after fairly long drives and heard it make a distinct "pop" as it returns to position after doing the EGR thing.

The codes, P0401/P1491, Insufficient Flow/Insufficient Lift, are vague. One would think it would be impossible to have one code without the other. The mystery is inside that control box.

Best suggestion is to get a repair manual and read the EGR section a few times and then grab a multimeter, pump-type hand vacuum tester, etc. and delve in and test that whole system.
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Old 01-23-2012, 03:29 AM   #16
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Default Re: Code P1491 everything replaced still getting code

Thanks, breakdrum. I don't know why but the light went off on it's own. All I did was snug up a couple vacuum hoses that seemed snug. My EGR doesn't have hoses to it. Maybe it was the Seafoam left in the tank working to clean things. Now if it would stay off.
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Old 01-23-2012, 03:50 PM   #17
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Default Re: Code P1491 everything replaced still getting code

Quote:
Originally Posted by gcondo View Post
Thanks, breakdrum. I don't know why but the light went off on it's own. All I did was snug up a couple vacuum hoses that seemed snug. My EGR doesn't have hoses to it. Maybe it was the Seafoam left in the tank working to clean things. Now if it would stay off.
If your EGR valve has no hoses attached, then it can't operate when the EGR solenoid applies vacuum to it. Obviously the Lift Sensor that crowns the EGR valve would not report mission accomplished to the ECU. A CEL is guaranteed in that scenario. If your EGR valve has been blocked off, then it sounds like the ECU is still looking for it and will place that code and illuminate the CEL every time that EGR solenoid applies vacuum and gets no information back. Blocked off, of course, means no EGR flow at all.
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Old 01-23-2012, 04:30 PM   #18
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Default Re: Code P1491 everything replaced still getting code

Quote:
Originally Posted by brakedrum View Post
Best suggestion is to get a repair manual and read the EGR section a few times and then grab a multimeter, pump-type hand vacuum tester, etc. and delve in and test that whole system.
i'll second that. getting the good one (Helms for around $60-75 used) pays for itself pretty quickly.

i looked through the troubleshooting procedure for P1491 briefly and it's pretty long, heavy use of the multimeter and starting the engine and running at certain RPM... but the results of most of the testing seems to lead to either a bad ECU or an open or short somewhere between the EGR and the ECU. If you can get your hands on a known good ECU, try swapping it out and see what happens. Also check all the wiring as well as you can for any looseness, breaks or other damage.
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Old 01-30-2012, 06:21 AM   #19
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Default Re: Code P1491 everything replaced still getting code

Quote:
Originally Posted by brakedrum View Post
If your EGR valve has no hoses attached, then it can't operate when the EGR solenoid applies vacuum to it. Obviously the Lift Sensor that crowns the EGR valve would not report mission accomplished to the ECU. A CEL is guaranteed in that scenario. If your EGR valve has been blocked off, then it sounds like the ECU is still looking for it and will place that code and illuminate the CEL every time that EGR solenoid applies vacuum and gets no information back. Blocked off, of course, means no EGR flow at all.
This model ('02) does not have a place to attach a hose to the EGR. CEL is still off. Thx.
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Old 02-11-2012, 11:50 AM   #20
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Default Re: Code P1491 everything replaced still getting code

For Tortis!
if you have gone thru and cleaned the EGR, Cleaned out the ports and checked the Vacuum lines heres how i got my light off afterwards.

unplug the power to the egr, turn on the ignition and the light should be off.
Turn the engine one for a sec, then turn off.
replug your power to egr and you should be set.

Worked in My Moms Honda minivan LOL
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Old 02-27-2013, 02:38 PM   #21
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Default Re: Code P1491 everything replaced still getting code

Tortis did that work for you? I have the same problem
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Old 10-23-2013, 03:24 PM   #22
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Default Re: Code P1491 everything replaced still getting code (tortis)

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alright, cel is on. P1491.

i am open to any ideas. i hate having my *** kicked when the opponent (the car) is trying to help. it has to be something simple.
can we get an update on what happened if possible?
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