New to Forum Life

[JRichy23]

This is my first forum post ever. However i do have automotive experience, i have worked as a tech for 7 years all of those years working on german cars. To the point, i own a 2004 Grand Prix 3.8 series III NA, i have owned it for almost 9 years, i purchased it with roughly 150,000 miles on it, it currently has 277,500 miles on it and is running strong, interested to know how many miles some other have. This vehicle is my daily and only vehicle i have done nothing major to it and had few problems, i have done the typical upper and lower intakes and very very regular maintenance. Most recently have replaced the entire steering system due to leaks. i currently with only putting a hundred dollars or so every few months have gotten the entire engine bay sealed and leak free, yay me, only items left on my list is rear suspension and struts/springs all the way around(will be looking into this later). To note everything on this vehicle aside from rims is stock. Love this car due to its reliability, will drive it till it dies, rebuild and do again, joking(kind-of). I have ran into a problem and seemed to have exhausted all my options aside from pcm error or engine not creating enough vacuum, only fault code on is P0401(egr insufficient flow), have no vacuum leaks(verified by using a smoke machine) i have checked all wiring going to and from the pcm to the egr, replaced the egr valve, removed intake to check for issues, none found. checked the intake side and the exhaust side of the egr, both free of any carbon. vehicle runs and drives very good. Aside from removing lower intake gaskets and re sealing just to be sure (recently done aprox 60k miles ago), pcm being bad im not really sure where to go any more. i have freeze frame data i can post tomorrow. Next thing on my list of things to do is check running vacuum. just have to find time at work

[FordMan77]

Welcome to the forum! Sounds like you have a well maintained machine there. Far as mileage goes I've got ~393,450K on my 00 GP GT currently and still running strong. Odo shows 443K but had an engine swap long ago. Trans is starting to die but that's to be expected at this mileage, lol... It owes me nothing at this point.

Regarding the P0401 code, see below:

DTC P0401

CIRCUIT DESCRIPTION
The powertrain control module (PCM) tests the exhaust gas recirculation (EGR) system during deceleration. The PCM does this by momentarily commanding the EGR valve to open while monitoring the signal circuit of the manifold absolute pressure (MAP) sensor. When the EGR valve is opened, the PCM will expect to see a predetermined increase in MAP. If the expected increase in MAP is not detected, the PCM records the amount of MAP difference that was detected and adjusts a calibrated fail counter towards a calibrated fail threshold level. The number of EGR flow test counts required to exceed the fail threshold may vary according to the amount of detected EGR flow error.

Normally, the PCM will only allow one EGR flow test during an ignition cycle. To aid in verifying a repair, the PCM will allow up to 16 EGR flow test counts during the first ignition cycle following a code clear event. Between 9-16 EGR flow test counts should be sufficient for the PCM to determine adequate EGR flow and pass the EGR flow test. If the PCM detects an EGR flow error, DTC P0401 sets.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient

CONDITIONS FOR RUNNING THE DTC

* DTCs P0068, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0201, P0202, P0203, P0204, P0205, P0206, P0220, P0300, P0335, P0403, P0404, P0405, P0502, P0503, P0506, P0507, P0604, P0606, P0641, P0651, P1106, P1107, P1125, P2101, P2108, and P2135 are not set.
* The engine run time may need to be more than 2 minutes .
* The Ignition 1 Signal parameter is between 11-18 volts .
* The AC Relay Command parameter does not change.
* The EGR position is less than 1 percent .
* The transmission is in 3rd or 4th gear.
* The Current Gear parameter does not change.
* The Intake Air Temperature (IAT) Sensor parameter is between -7°C and +100°C (+19°F and +212°F) .
* The Engine Coolant Temperature (ECT) Sensor parameter is between 75-126°C (167-259°F) .
* The Engine Speed parameter is between 1,000-1,500 RPM .
* The Manifold Absolute Pressure (MAP) Sensor parameter is between 17-43 kPa, 20-43 kPa for supercharged.
* The Barometric Pressure (BARO) parameter is more than 74 kPa .
* The Throttle Position (TP) Sensor parameter is less than 1 percent .
* The Vehicle Speed Sensor parameter is between 45-113 km/h (28-70 mph) during deceleration.
* The Idle Air Control (IAC) Position parameter does not change more than 3 counts while the above conditions are met.
* The vehicle will need to be driven more than 80 km/h (50 mph) , and then allowed to decelerate. When the vehicle is decelerating, while meeting all of the criteria listed above, the PCM will enable the EGR flow test to run. As the EGR flow test is running, you will see the Desired EGR Position parameter and the EGR Position Sensor parameter on the scan tool momentarily change from 0 to a calibrated value above 0. Additionally, the EGR Flow Test Count parameter on the scan tool will increment when each EGR flow test is completed.

CONDITIONS FOR SETTING THE DTC
The MAP changes monitored by the PCM during the EGR flow tests indicate an insufficient amount of EGR flow.

ACTION TAKEN WHEN THE DTC SETS

* The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
* The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC

* The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
* A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
* A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
* Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
Inspect for the following conditions:

* A vacuum restriction to the MAP sensor-A skewed MAP sensor reading can cause the PCM to read incorrect MAP changes during the EGR flow test.
* An engine that is running poorly due to a mechanical condition such as worn piston rings, worn camshaft, etc.-These types of conditions can cause low engine vacuum and thus can cause a less than expected MAP changes during the flow test.
* Excessive back pressure in the exhaust system may cause this DTC to set. This condition can cause low engine vacuum and thus can cause a less than expected MAP changes during the EGR flow test. Possible causes of this could be a restriction in the exhaust system or non original equipment manufacture (OEM) exhaust parts.
* Exhaust system leaks can cause an insufficient amount of EGR flow through the EGR valve. This condition can cause a less than expected MAP changes due to insufficient exhaust back pressure. Possible causes of this could be a leaking exhaust system, a leaking EGR pipe, or non original equipment manufacture (OEM) exhaust parts.
* A restriction in the intake manifold such as carbon deposits and casting flash

[BillBoost37]

Very likely the issue is the map sensor. That is how the pcm monitors the flow when it commands the egr to open or close. Check out the map. Ensure that the passage it sits in is not blocked (which would be odd..but possible)

[JRichy23]

Live data freeze frame. MAP sensor is brand new broke&replaced when i re sealed upper intake looking for any issues.

[BillBoost37]

I have seen new parts be bad out of box.

Do you see changes in it while you are scanning if you blip the throttle etc?

[JRichy23]

I have seen new parts be bad out of box.

Do you see changes in it while you are scanning if you blip the throttle etc?

under load? at idle? and to make sure we are talking about changes in the MAP, i can do this while over lunch and see what results i get

[BillBoost37]

At anything..if you tap the throttle.. you change the air flow in the intake and the map should register it. Do it in P and then in gear if you aren't seeing sufficient changes, then the map may be bad or not seated properly. Give it a double check.

I saw a guy who swapped the EGR three times to try and fix the code. Ended up the map wasn't seeing the expected change and his map had suffered an issue when he was doing his intake gaskets. Sounds like yours did as well but you replaced it. I'd think that's worth double checking. You've already checked the EGR etc and didn't find an issue from what you've said. And these cars aren't really all that complex, there's only a couple of things that'll cause the code. I'm sure you'll get it fixed up in no time.

[JRichy23]

Update: had free time at work today, looked into my issue. All vacuum reading at idle with scan tool from MAP Live date unless otherwise said.

Engine running around 6inhg of vacuum steady, found injector o-rings faulty, replaced all injector o-rings vacuum went up to a steady 10inhg. digging a little further into issue and most likely needing LIM gaskets anyway i decided to do the LIM job, found them definitely at the end of there life but nothing to suspect failure causing major leaks. Interesting note, when removing upper intake i have oil puddles in the corners of my lower intake enough to just cover the bolt, not sure how common that is or if is an issue(i used sillicone on all bolt threads in LIM). After completing the LIM job found engine now at 11.6inhg. Shut off engine, removed brake booster hose and placed manual vacuum gauge at the booster end, started engine found at 18inhg on the manual gauge, Forgot to look a live data while like this; put booster line back in place, removed MAP sensor kept plugged in, installed vacuum gauge, found 18inhg vacuum at gauge.

Further diag:
Engine off Ignition on, removed MAP, is reading 29.6inhg (consistent with BARO) place under various vacuum with manual vacuum pump for example it placed under 10inhg with the pump MAP reading on scan tool would go from 29.6 to 19.6inhg, so i placed under different vacuum and all numbers were correct.

MAP still removed ignition on engine off found with no vacuum applied MAP voltage is 4.7v at MAP with 10inhg vacuum aprox 3.5v and at 20inhg aprox 1v, In my opinion all readings are good(very well could be wrong)

Suspecting brake booster i drove vehicle home and let sit for 4 hours and removed booster line from booster and i could hear it releasing vacuum and lots of it, checked valve also and is working properly.

MAP, PCV valve, Housing, Spring and all O-rings all under 2months old.

Very little to no vacuum at the oil fill cap
Checking if MAP will change when pushing down on MAP sensor at idle to check to make sure is seating properly.

Very well could be at some loss of vacuum from piston rings but since my readings are good at my booster line makes me question that.

Thank you for the assistance.

Edit:
On my way home about a 20 min drive CEL (P0401)came back on and freeze frame MAP was at 9.3inhg with RPM of aprox 1200