I've been chasing an intermittant egr operation, with a code 12. Tried changing the egr valve, no change. Ran a complete trouble shooting flow chart and cannot find anything definite. Good vacuum, 12 volts at the blk/y wire, egr solenoid valve operating correctly, 5 volts to the lift sensor, and now the chart says to connect a test harness. Well, I don't have one of those. Ran a few additional tests and found I am losing the ground at the pink wire at the EGR solenoid valve. If I back probe this connector to ground everything works correctly every time. I am assuming the ECM controls the ground side of this circuit? But I can't confirm this anywhere? Does anyone have experience troubleshooting this kind of thing or a better wireing diagram?
1992 Accord
Thanks, Mark

 

The ecu will ground the ground side on and off continously when it wants the egr to function. It does this to get the vacuum at a constant 3 to 4 inches or so. This happens during light throttle and cruising situations. You can attach a vacuum gauge using a t-fitting in between the egr valve and the egr solenoid and run it into the cabin through the firewall and watch it as you drive, preferably with someone else driving and you with the gauge and monitor it. vacuum should be around 3 to 4 inches when you are cruising.

The only time this code is thrown on an obd1 car is when the egr valve itself doesn't lift up and down. This code is only thrown when the lift sensor doesn't detect any movement in the egr valve for two straight drive cycles.

 

The number one cause of this code is that the egr valve gets caked up and no longer is able to move freely. It can also be the egr valve lift sensor goes bad but since you got two egr valves now I think you should look at if they are caked up with carbon, then do the drive test.

 

Thank you for the feed back, I appreciate your time. I had already done the vacuum gauge test while driving, it showed normal vacuum a few times then stops, then the check engine light comes on. Once it stops working it won't work again until you shut off the engine and restart it. Then it will work again a few times, then nothing. To me it just seems like I'm losing the ground to the solenoid circuit because everything else seems to be working as designed. The egr is new, it holds vacuum and the passages are clean, engine dies quicly at idle when valve opens.
Thanks, Mark

 

Then your issue could be your ecu. I would swap another ecu and see what happens. This assumes you've tested and everything appears ok.

 

Now that I think of it you should check the lift sensor for operation. It could either have bad wiring or the sensor could be bad. I know you said you have used two different egr valves so it could just be the wiring.

 

Did you check the egr ports on the intake manifold? They usually cake up with carbon.

http://home.comcast.net/~em-engineering/T2T013.pdf

 

that won't have anything to do with the car throwing that code tho

 

To me the wiring is all ok because the EGR operates fully, opens, holds vacuum and kills the engine quickly as long as I back probe the pink wire (ground) to the solenoid valve. Passages are clear. I have another ecm I'm going to try tomorrow and see what happens? Do you know what sensor data does the ecm use to determine when to ground the circuit so the egr will open? I can only figure it must be using map sensor info which would sense engine load and vacuum? What do you think? Thanks, Mark

 

I know it will use throttle position and coolant temperature and rpm's...i'm not so sure about map sensor

 

Yes, the ports have been cleaned, the egr works great and kills the engine very quickly when it opens, I can open it with my vacuum pump or when I back probe the ground to the soleniod valve. when test driving with a vacuum gauge shoved under the wiper blade it will operate 2-3 times when accelerating down the road then it quits completely until you stop, shut off the engine and try again. This thing is driving me nuts........

 

ok let's be clear...the egr system has only one check on it..when the egr functions it will test the system to see if it's working properly..it will use the lift sensor to detect if the system is working properly because it knows where the egr valve is supposed to be at any given moment and if it's not there it will throw the code...it has no way of knowing if the ports or clogged it can only detect the lift sensor

I've seen your issue before and normally when what you're saying is happening occurs the problem, for some reason, is the ecu.

 

Thought I should get caught up and let you know what I eventually found with my 92 accord EGR problem. I tried a replacement ECU, didn't make any difference! Got it from E-Bay cheap so not a big deal. Eventually I just went to the local Pick-A-Part wrecking yard and bought a firewall "Black Box" installed it and everything works fine, no more code 12. It all seemed to be working as designed yet I was missing something and this only cost $23.
Thanks again for your advice. Take care, Mark

 

The only thing I can imagine being bad in that black box is the solenoid but I've never heard of one going bad. It could have clogged up with gunk. That's why it's best to apply battery voltage to it and while it's open spray it out with some carb cleaner. You will hear it click when you apply voltage or it's bad. The only other piece is the vacuum control device and I gotta think that thing can't really go bad.

Hopefully this helps any other future member.