Check engine light on my 99 SH -insufficient egr flow (think it's p0401)keeps coming on-changed the valve, cleaned out the intake ports, it's still throwing the code. Next step Honda recommends is changing the ecu, however don't think that's the problem-the light comes on fairly consistently on trailing throttle (coasting downhill, slowing for toll booths, etc), think it would be more random if the ecu was acting up, also takes a few days to come back, or a few hours at freeway speeds. Car also has cat back (NOT recently installed)-could that be the problem-insufficient exhaust pressure to create enough egr flow, helped along by aging or something else. Any help appreciated, I'm stumped and don't wanna buy a new ecu if that won't fix the problem, spent enough already.

 

You sure you have the ports cleaned out good. For a test open the valve w/ your fingers with the engine idling (be careful not to put a hole in the plastic diaphram). This should stall out the engine if you open it abruptly enough. If it doesn't almost stall the engine then you need to clean out the intake ports more.

No where for a p0401 does the flow charts take you to a section where you need to replace the ecu.

Also make sure you don't have p1491 set also cuz the helms manual says to check that out first. Those flows show ecu replacement.

 

I had a mechanic do the replacement/cleaning, little too much grey hair for that now, however been dealing him for 15 years, know him well, he cleaned it twice, as much as possible without removing the intake. No 1491 as far as I know, did throw for one o2 sensor a little while ago, replaced that and it went away. My mechanic talked to contact at Honda dealer, that's where the "replace ecu next" came from.

 

I'd highly recommend running the quick test in my previous post. It's free and is super easy - no tools, no need to get on your back, no jacking up the car, no taking anything apart. The most difficult part is probably trying to figure out where the EGR valve is and waiting 5 mins for a warm engine.

I'd hate for you to have to spend more money on something you possibly don't need. If the test above passes the do get a new ECU; although your mechanic cleaned it twice he may have not cleaned to good enough. Ask him how he determines the port is clean. The test above is the only way I know.

Per the manual the ecu has a couple monitors to figure if the EGR components are working. First it figures when to "Recircuilate the Exhaust Gas" to the intake. Then there's a logic check, to determine if the valve physically moved because it works off a solenoid valve and vacuum (p1491/p1491). Then via the MAP sensor it figures if the event really happend. If the Map sensor was flakey/dead you'd get a (p0107, p0108, p1128, p1129). If the ecu was bad (had a bad input/output pin) then you would probably get one of these other codes too.

 

Ok, ran that test 2 ways-disconnected the vacuum line and sucked on it to open the egr, engine rpm dropped but did not stall out, then manually jumpered the solenoid to the battery (to also check if the solenoid was working)-same thing, rpm dropped but did not stall out, engine seems to labor at idle with egr open, drops by maybe 200-300 rpm. Anyway the solenoid is eliminated as a problem as well, still (I think) leaving only the dirty intake or ecu, definitely leaning towards the intake at this point, posted this question also to honda-tech and got pretty much same advice-clean the intake. What about replacing it-skunk2?? How much do you gain at the top end, how much do you lose at the bottom end?

 

okay that's the proper way to check using a vacuum guage- mouth works fine too (not sure about the 8" vacuum). The only way I've gotten mine to stall is by opening it very quickly w/ my fingers on the diaphram. Aside from that the laboring idle is whats expected. Humm, maybe mine needs more cleaning, need to check the Helm's on that to see if it's supposed to stall.

I suppose the MAP sensor may be getting "tired" not reading the slight pressure difference - but that guess is just as good as saying it's the ecu. Possibly cheaper/easier to swap than an ecu. Borrow a friends, if you're lucky most hond/acura parts are the same, at least my wifes 97 CL and my 97 Prelude are a lot alike.

Oh and not sure what year your Prelude is but 97 (and possibly others) has an emission warranty extension 14yrs 150k miles. If you haven't done this extenstion replaces the plugs, distro, cap rotor, wires, oil for free. Not quite sure what else they look for but egr is part of your emmisions system.

Keep us posted on what you find...

 

I feel ya man, I get the code 12 egr on my h22a in my honda accord. I have cleaned the ports and paid $200 for a new egr valve and still get a cel that comes on. Should I try the map sensor thing or the egr valve solienoid?

 

Not sure about the solenoid on the accord, doubtful that the MAP sensor would be bad, the ecu should throw a code for it if it gave a value out of range. Was you're IM taken off and cleaned? You may be able to use the "suck" test on the solenoid described above, or jumper it to see if it's working OK. I haven't decided what to do yet, the cel doesn't affect performance hardly at all, so no hurry. Will probably replace the IM with skunk2 as first step in an upgrade.

 

Yea I think its my IAB diaphram on my intake manifold. Its vacuum hose inst connected to anything. I found this vacuum routing for the h22a and it shows that the vacuum line should go from IAB diaphram to the IAB control solienoid, well I got under my car and looked under the IM and there was no IAB control solieniod so maybe its somewhere else or they bypassed it with my swap? So I dont know if it works correctly or not?

 

I have the exact same EGR problem on my 99. checked the cat, the coil, changed the valve, changed the solenoid, done a gum-out to the intake, checked ALL the wiring, and code continues to appear!!!!!!!!!!!!!

Any help?? did u fix your problem??? I'm soooooo lost!!!!!!!!!

thanks!!!