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Thread: Yet Another Code 12 EGR System Thread

  1. #1
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    Yet Another Code 12 EGR System Thread

    Hello all,

    Please forgive me if I'm in the wrong area.

    I have read through the countless threads on this topic and decided to tackle pinpointing the problem today. I am now more confused than ever after tackling the black box an am hoping someone can help fill in the blanks in my knowledge. After all, I'd love to be able to drive it around more than a couple minutes without the red "PGM-FI" light coming on.

    My Car is a 1987 Honda Accord Hatchback LX-i Manual trans (Fuel Injected)

    I'll start with things I know are good:

    EGR Valve: Looks to be brand new, I removed it, no carbon at all, opens and closes with vacuum, no leaks. Looks like someone was here before.

    EGR Solenoid: Clicks when you apply battery voltage, if there is no voltage the valve is open, meaning you can suck air through it. when I apply 12 volts to it I can no longer suck air through it so it seems to be operating

    AIR Chamber??: It looks like cylinder with three nipples, two of them are close together. Top one goes to the EGR Solenoid, middle goes too the EGR valve bottom goes to the CVC Valve? its a UFO looking thing (Green and white saucer I think?) if you suck on the side that the EGR solenoid plugs in, it will send vacuum to the EGR valve, if you suck on the EGR valve side it will send vacuum to the EGR solenoid. If you suck on the bottom nipple, it goes nowhere... plugged or supposed to be that way? the flying saucer (what I think is the CVC) supplies vacuum with the engine running to the bottom nipple of the air chamber which leads me to believe that the CVC is working

    Here is where I get confused.

    After reading the forums, I've come to the conclusion that with the engine running, if I manually turn on the EGR solenoid while the engine is idling, it should kill the engine. It doesn't do that, engine still runs happily. So I checked for vacuum at the manifold (where the solenoid gets its vacuum from) and there is no vacuum there.. if I then suck on that hose I can kill the engine when its idling and the solenoid unplugged.

    I guess it makes sense that there would be no manifold vacuum because if there was, with the solenoid being off=vacuum on=no vacuum (off appears to be default), it would be killing the engine at idle every time. So then the question becomes how is manifold vacuum controlled? There was no vacuum there at any RPM.

    With this in mind I assume that would mean that the solenoid is being commanded on by the ECU at idle, the Black and yellow wire has 12 volts on it but the ECM doesn't appear to be grounding it at idle which would mean that its calling for vacuum to be sent to the EGR at idle. If I test for voltage using the ECM as ground it fluctuates between 2-9 volts. stays mostly at 2 volts. Is this a duty cycle thing with the ECU controlling the EGR valve at idle or is my ECM bad?

    I'm hoping I'm making sense and that you guys can help me understand what's happening and how this system is supposed to work.

    As fair as I can tell I have a bad intake, bad solenoid (appears to be operating backwards?) or bat PCM... or all of the above.

    Ask any questions you have!

    Thank you!



  2. #2

    Dr_Snooz's Avatar
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    Re: Yet Another Code 12 EGR System Thread

    Wow. You certainly get points for thoroughness. And double points for perseverance. I guess my first question is how are you troubleshooting this? Are you following the flowchart in the manual, or reading around and testing based on that? I assume you're getting the 12-blink code from the flashing LED on the ECU under the driver's side seat. If not, then verify that first. My only question after that is, if you apply vacuum directly to the EGR valve with the engine running and warm, what happens?
    Dr_Snooz

    "I like to take hammers, and just break stuff, just break stuff." - Beavis


    1989 Honda Accord LX-i Coupe, 240k miles, MT swap, rear disc swap

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  3. #3

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    Re: Yet Another Code 12 EGR System Thread

    Does the car have any symptoms other than the check engine light?

    Have you used the OEM Shop Manual to diagnose the entire EGR system?

    1988 Honda Accord LSDX-I

  4. #4


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    Re: Yet Another Code 12 EGR System Thread

    https://www.3geez.com/forum/showthre...ode-12-problem

    Verify thru the manual that the voltage you are reading is supposed to be 0-12 volts DC and not 0-5 volts.
    1988 Lxi owner since August 1995
    336k miles running strong!
    Now running E85.

    Oldblueaccord <<< MY YOUTUBE PAGE!

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    Re: Yet Another Code 12 EGR System Thread

    Dr Snooz: Thank you! I figured I would try to get all my ducks in a row before asking for help.

    My understanding and troubleshooting techniques come from the threads on this site of various recommendations from members. The ECU is flashing 12 times with a pause in between, no other codes. When I get home I will warm the engine up and test then report back.

    Conozo: the idle when its warm will idle at 800 RPM but it doesnÂ’t seem smooth, not sure if its just these cars. Its hard to explain, the engine is smooth at all 4 cylinders and sounds good when youÂ’re outside the car but when you go inside you can hear/feel the engine vibrate the car. IÂ’m of the thinking that its just how the motor mounts are or maybe they are just old, not sure.

    When the EGR code happens it will bump idle to 1200 RPM, engine is nice and smooth when that happens. It used to fluctuate between 1200 and 1700 back and fourth but between the air screw adjustment and fooling around with the black vacuum box that seems to have gone away. Now there is maybe a 50 RPM variance at 1200 RPM.

    IÂ’m a little lost with the manuals, I have the design manual, general shop manual for 86-89, and the electrical manual for 89 thanks to Dr Snoozs signature. I didnÂ’t see a fully fledged EGR troubleshooting section that lines up with what people talk about in other forums. What I have in the general shop manual is EGR Inspection.. (whats KX and KQ and how can I tell which one I have?) Is there a different manual I need?

    Oldblueaccord: That thread was a good read, not sure what manual they are getting those steps from.. all I have is the Design manual, General Shop Manual 86-89 and electrical manual for 89. In the General Shop Manual, it has an EGR Inspection section that isnÂ’t as robust as those people are mentioning. At one point they talked about a wiring harness tester. There is nothing in the general shop manual that I could see that has that unless I'm looking in the wrong place. Do I need a different manual?

    Thanks guys!

  6. #6

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    Re: Yet Another Code 12 EGR System Thread

    Quote Originally Posted by UsernameAlreadyTaken View Post
    IÂ’m a little lost with the manuals, I have the design manual, general shop manual for 86-89, and the electrical manual for 89 thanks to Dr Snoozs signature. I didnÂ’t see a fully fledged EGR troubleshooting section that lines up with what people talk about in other forums. What I have in the general shop manual is EGR Inspection.. (whats KX and KQ and how can I tell which one I have?) Is there a different manual I need?

    Oldblueaccord: That thread was a good read, not sure what manual they are getting those steps from.. all I have is the Design manual, General Shop Manual 86-89 and electrical manual for 89. In the General Shop Manual, it has an EGR Inspection section that isnÂ’t as robust as those people are mentioning. At one point they talked about a wiring harness tester. There is nothing in the general shop manual that I could see that has that unless I'm looking in the wrong place. Do I need a different manual?
    Get the 89 service manual from Snooz's sig

  7. #7
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    Re: Yet Another Code 12 EGR System Thread

    Dr Snooz, after letting the engine warm up and sucking on the EGR hose it will kill the engine no problem.

    ShiRen, Thank you for pointing me in the right direction although after looking at the system there seems to be some major differences between my system and the one in that manual.

    In the manual there is an EGR solenoid A and B, as far as I can tell I only have one solenoid in my control box and its in the same spot that the “Vacuum Holding Solenoid” is on page 11-8 (or 115) . It has two pairs of wires going to it on mine though.. The EGR Solenoid A and B in the manual look to be in the position that (what I think) my MAP sensor is

    I also have a hose 17 that goes from my EGR Solenoid to the intake manifold. That doesn’t exist in that service manual. It doesn’t seem that the 3 nipple air chamber thing that connects my EGR Solenoid and CVC to my EGR valve exists in the 89 manual. I also don't see the CVC in there anywhere either.

    Still at a bit of a loss, would it be beneficial for me to upload any pictures of the inside of the Control box?

  8. #8
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    Re: Yet Another Code 12 EGR System Thread

    Alright fellas, I stumbled across this thread and I think it answered all my questions

    https://www.3geez.com/forum/showthre...-Accord-LXI-FI

    It sounds to me like the CVC is supposed to supply constant vacuum to the both hoses on the Air Chamber. Vacuum comes in the bottom of the chamber and is fed to line 16 (EGR) and 17 (Solenoid) The reason why I can suck air through it when its off and not when its on is because it’s actually venting the vacuum supplied by the CVC INTO the intake manifold. When the ECU wants to command the EGR open, it will tun on the EGR solenoid which shuts off the vent and causes vacuum to be sent to the EGR Valve.

    They mentioned blowing air through all the ports on the air chamber further confirming my theory that all ports are supposed to be open and free flowing. Currently the bottom one is clogged, cant suck air through it.

    Let me know if that makes sense, hopefully I can get to it tomorrow and report back. Its supposed to storm so maybe, maybe not

  9. #9

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    Re: Yet Another Code 12 EGR System Thread

    Quote Originally Posted by UsernameAlreadyTaken View Post
    there seems to be some major differences between my system and the one in that manual.
    Yeah, we ran into this once before. You can follow the 89 manual as far as it will take you, but you really need the 87 manual. Which could be hard to find. Here's a link, though I have no idea if the site can actually produce the manual in question.

    1987 Honda Accord Factory Service Manual – Original Shop Repair - Factory Repair Manuals

    Not even Helm is printing them anymore. Somebody needs to scan an 86/87 manual for us.

    Let us know how far you get with the 89 manual.
    Dr_Snooz

    "I like to take hammers, and just break stuff, just break stuff." - Beavis


    1989 Honda Accord LX-i Coupe, 240k miles, MT swap, rear disc swap

    Shop manual downloads available here: CLICK TO VIEW

  10. #10
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    Re: Yet Another Code 12 EGR System Thread

    I purchased an 87 Shop Manual from ebay, should come in next week. In the meantime (hopefully later today) I’ll remove the air chamber and blow it all out.

    I’m thinking that will solve my problem but I’ll report back.

    If I can figure out how to put it into a PDF, it I’d love to upload it for you guys. We gotta keep these cars on the road!

  11. #11

    ShiRen's Avatar
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    Re: Yet Another Code 12 EGR System Thread

    One option would be to donate the book to the internet archive https://help.archive.org/hc/en-us/ar...ernet-Archive- I would consider buying it and sending it to them, but that is $60 that I am never going to see again, so if anyone wants to, a few of us can pitch in to buy another copy solely to send to the internet archive. No telling when the scan will be done though, but they might be willing to negotiate.
    A temporary solution would be to compare the vacuum diagrams and wiring diagrams and only scan the relevant pages to the parts that are different.
    Also, its no factory manual, but this exists https://archive.org/details/hondaaccordautom00brow
    I found another manual, seems to be multiple manuals combined. Find the 86-89 manual here: https://www.dropbox.com/sh/k4p1ugrib...nkN1KHF_a?dl=0
    Last edited by ShiRen; 04-14-2022 at 06:01 AM.

  12. #12
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    Re: Yet Another Code 12 EGR System Thread

    Shes all set guys, it was the air chamber. The hose that connects to the CVC was plugged so I fired the old air compressor up and blew it out with throttle body cleaner, drove it for probably 20 miles and no light! Before you couldn’t drive a few miles without it coming on.

    As a test I took the number 17 hose off the intake and the hose had suction. When I blocked it with my finger it made the engine stumble down to about 20 RPM. Didn’t stall. Looks like its good enough for the computer. Thanks for the help guys!

  13. #13

    Dr_Snooz's Avatar
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    Re: Yet Another Code 12 EGR System Thread

    Glad to hear it! Have fun!
    Dr_Snooz

    "I like to take hammers, and just break stuff, just break stuff." - Beavis


    1989 Honda Accord LX-i Coupe, 240k miles, MT swap, rear disc swap

    Shop manual downloads available here: CLICK TO VIEW

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