Fooling the PCM to get the EGR monitor ready

I put in longtubes with emissions fittings and threw the PO400 code...I had Ion edit the EGR out but now I have to pass an OBDII scan for the first time. I'm sure there's lots of members in similar situations with tightening emissions laws.
With the EGR edited outSES light will be off but the egr monitor will always read not ready...
We're allowed 2 not ready monitors and I can't seem to get the catalyst and AIR monitors to read ready on my carafter 3 weeks of driving.
My Evap, O2, and O2 Heater monitors read ready.
So I needed 1 more monitor to pass.
The EGR PO400 code is set off because the backpressure is not as strong as with the stock manifold, due to the placement of the EGR tube on the single header pipe with longtubes. I made my own emissions fittings and should have made the EGR tube bigger. It seems to be an OBD2 specific problem on cars with other brands of headers too, probably because the EGR is more sensitive than OBD1.
Here is why the code is set off: the PCM commands the EGR valve to open, then the MAP sensor takes a reading of manifold pressure. It measures this rise in pressure as a low rise in voltage...but if the pressure hasnt risen enough, the voltage reading is too low and a P0400 code is issued.
Here is how to trick the computer:If deleted, enable the EGR PO400 diagnostic test in LT-1 Edit under file, engine, diagnostic tests, and reflash the PCM or get an updated tune.
Unplug the 2 wire weatherpak going to the EGR solenoid, and splice it onto a 12 volt relay. From there...off the other side of the relay, one wire gets spliced onto the rear wire of the MAP, and another wire gets spliced onto the center green wire of the MAP, with a 75 ohm resistor or 2 150 ohm resistors in parallel. The front MAP wire stays as it was. Now when the PCM tells the EGR to open, it is actually energizing the relay, then sending the properly tuned voltage (because of the resistor) onto the MAP circuit and the computer thinks the manifold pressure has risen. The result? No more SES light and my EGR monitor reads ready after less than 100 miles.
It seems to take almost 2 tanks of gas to get everything to reset.
I used wire strippers and carefully pulled the insulation back to pinch the wires in. Better connectors can be used if wanted but I'm gonna soldier my pinched connections and run the wires discretely with connectors to the relay.
So now I've got the 1 more monitor I needed to pass my scan.
Just thought I'd pass this along to help someone with the ERG monitor not ready pass their OBDII test.

This is great info! At the risk of sounding lazy/ignorant, can you post more specifics on which wire of the egr harness goes to which terminal of the relay? I am in the same position with longtubes, and was about to splice into the air fitting on tube #2 to get my EGR back, but I guess it won't work....

The wires from the EGR will work either way.
I had a few 12v relays from an alarm system.
I tried them with a power supply and it didn't matter about the polarity to make the relays engage.
Just unplug and pinch into the egr wires and hook the wires to either side of the relay.
One of my relays was on unless power was applied and that didn't work right because the pcm wouldn't get the proper signal from the map sensor.
Make sure you check that the relay will work properly with the 75 ohms applied across the back 2 map wires when the relay engages.
I had one with 5 tangs that had 1 side on and 1 side off when powered so I just made the right connections and then it worked.

My old SLP 96-97 CARB legal shorties used 2 pipes to take the egr off of.
They didn't throw the PO400 code.
I've also seen headers with egr tubes from every pipe converging together for enough back pressure.

If I'd welded up egr lines from 2 pipes and made the fitting bigger it would have worked.
But this is a great easy solution.
Maybe if I pull off my header some time I may rework the EGR to see if it will be functional.
After I get my scan I'll plug the egr solenoid back in and see if it still works without throwing codes and being monitor ready.
As I still have the egr valve it doesn't hurt anything in the engine when engaged even with less backpressure.
Got a 58 mm TB and ported intake to put on as soon as I've passed.

I'll tell you exactly how to get the EGR monitor "ready", because it works for me.

Leave your EGR solenoid hooked up and plugged in. Ditch the actual EGR valve.

OK to turn off P0400. What you do is go into Engine parameters and set the EGR values to max RPM and max MAP so that the PCM never commands EGR on.

the PCM runs the test on the solenoid, so since its still hooked up, but never commanded on, I get a "ready" status after driving the car long enough.

I use 02 sims for the rear O2s, the only monitor I actually have disabled is AIR, but for 1996-1999 you only have to have 3 of 5 ready to pass.

The 5 are:

AIR
EGR
02 sensor
02 sensor heater
catalyst efficiency

Well there's always one more than 1 way to do something.
Maybe after i get my car inspected next week, I'll redo my program and see what happens.
It seems to take a week or more for the monitors to reset so I'm not gonna do it now as the relay trick works well and I'm almost there.

What numbers did you enter for MAP and RPMs in LT-1 Edit?

i know this is a couple weeks old but im running into a simular problem. how is the lt4 car different in programing so that the egr isnt even there and doesnt need to be ready

It has to be a Corvette LT4.... they are the ones that had no EGR. The LT4's that were put in the 97 SS's and 'Hawks had the EGR valve and the programming, AFAIK.

My old SLP 96-97 CARB legal shorties used 2 pipes to take the egr off of.
They didn't throw the PO400 code.
I've also seen headers with egr tubes from every pipe converging together for enough back pressure.
Are you sure you aren't confusing the two AIR tubes with the single EGR connection?

i know this is a couple weeks old but im running into a simular problem. how is the lt4 car different in programing so that the egr isnt even there and doesnt need to be ready
Exactly. The LT4 Vette has a different program in which there is no EGR test. Unfortunately you cannot run a Vette program in an F-body. "Why not delete the EGR in the F-car program?", you might ask. With LT1-Edit and Tunercat you are just changing data in tables. To completely delete the EGR portion would involve changing the code logic, which is much harder (I would guess next-to-impossible since no one has done it beyond the "blm locker") to do.

The EGR code is deleted in LT-1 Edit by disabling the PO400 Diagnostic test on side one. I compared my stock program to the one Ion sent me with the EGR deleted.
I reenabled the EGR test and reflashed my pcm when I hooked up the relay and got my 1 more ready monitor I needed. Now I'll pass the test.
The reason the vette didn't have the EGR is because of the cam. With enough overlap there's EGR happening without needing a valve.

For what it's worth, EGR is disabled on the LT4 Vette the same way. The codes are disabled but the EGR enable parameters are intact.

Chris 96 WS6's way is the easiest way to do it though.

Hey Ion, I'm finally getting my emissions sticker on friday.
I have 2 monitors still out but I'll pass.
When I put in my 58mm and ported intake maybe you could set the EGR parameters like chris said in the updated tune.
That way I'll have my monitor without this relay stuff.
I was looking again at the LT-1 Edit parameters page last night.
I'm a little unclear here about the EGR. I can see where to set the engine parameters for RPM and MAP but do I disable the PO400 Diagnostic low delta test as you had on my S/C program and chris seemed to be saying?
Send me a pm if you can.
BTW your S/C program is working great with the 9 lb pulley with no pinging or alky injection yet (coming soon as I got unexpectedly distracted for the last month)
My TP Enhancer was giving me a little pinging so I took it out and now everything is great.

I got a PCM tune by Ion...will pullling the plug on the battery reset the specs he made it to? Or is there a special way to "flash" the PCM?

I pulled the positive terminal on my battery for my LT header installation, and would kind of be bummed out if it reseted my PCM!

The "program" data is in non-volatile memory. The only thing you lose when you pull the power to the PCM is the stuff stored in volatile memory, like the long term fuel corrections and the learned idle settings. Your "tune" will still be there.

Does anybody happen to have detailed pics and part numbers for doing this? Where can I get this relay and what do I ask for? What about the resistor? I see it says ONE 75 ohm or TWO 150's in parallel? :confused: Im gonna HAVE to do something about this dang SES light and this is the most cost effective solution Ive seen so far. I dont have LT1 edit and theres nobody close that I know of who can do it for me. Putting the cats back on just ISNT an option due to cost and loss of performance. I am gonna change the LM resonator and put on the LMII muffler and see if that helps any, but i seriously doubt it.
The whole problem started when I deleted the cats and put on a Loudmouth exhaust system. I put 02 sims in place for the rear sensors. A few miles after install and Im getting the dreaded po400 code. Everything else is fine except for that.

Sent you an email.
Anyone else who wants to make an egr simm for the P0 400 code PM me.

Got it! Thanks! Ive spent all weekend mulling it over on what route to go, and Ive ALMOST decided to just go back with some high flow cats and be done with it.

can someone explain the first method a little better to me..like with part numbers..im not very good with this whole relay,resistors, and wiring stuff..i need it explained"for a dummy"

I'll tell you exactly how to get the EGR monitor "ready", because it works for me.

Leave your EGR solenoid hooked up and plugged in. Ditch the actual EGR valve.

OK to turn off P0400. What you do is go into Engine parameters and set the EGR values to max RPM and max MAP so that the PCM never commands EGR on.

the PCM runs the test on the solenoid, so since its still hooked up, but never commanded on, I get a "ready" status after driving the car long enough.

I use 02 sims for the rear O2s, the only monitor I actually have disabled is AIR, but for 1996-1999 you only have to have 3 of 5 ready to pass.

The 5 are:

AIR
EGR
02 sensor
02 sensor heater
catalyst efficiency


so what makes the o2 sensor heater and cat. efficiency work?