2000 Venture 3.4 165K

Vehicle has intermittent P1404 (and sometimes P0404). EGR valve appears to function normally. Scan tool shows actual EGR position of .9V at startup and learned EGR closed position is .9V. When valve is commanded open during testing, actual EGR position matches desired EGR position and EGR error is 0. When valve is commanded closed, actual EGR returns to .9V.

As vehicle is driven, the learned EGR closed position value begins to incrementally drop and will fall to as low as .4V after a few miles of city driving. (It'* possible it could fall further, but I haven't driven it long enough with the scan tool to see how far it might fall.) The learned closed position value should stay constant. When the PCM commands the valve closed during driving (e.g. at a stop), the actual EGR position consistently returns to .9V but since the learned closed value has changed the PCM thinks the valve is staying open and eventually the P1404 triggers when the difference between learned closed and actual closed is >.2V. Sometimes P0404 will also trigger if the vehicle is driven long enough and the EGR error has gotten high enough.

Once the learned closed position voltage has dropped, it will not rise until restarting the engine. Then the learned closed position will again show .9V and the cycle will repeat. Two different EGR valves yield same behavior, although the closed position voltage on the second valve is .8V. Because the learned closed position value does not stay constant and drops, it seems like the vehicle might be in perpetual learn mode but that implies the minimum actual EGR position voltage would have to be dropping as well. However, the actual EGR position never shows below .9V.

The values are all based on the scan tool reading the PIDs.

I've seen references to TSBs and PCM updates related to EGR calibration on some vehicles around this time period, but AllData does not show any TSBs for my vehicle. A local dealer also claims there are no updates based on the VIN.

PCM replacement is one of the fixes in the diagnostic sequence, but does anyone know if something other than a bad PCM could cause the learned closed value to drop rather than stay constant? The vehicle runs fine and has no other issues and no other codes, just the EGR. If it is the PCM, is it possible that it is not a hardware issue, but maybe just a software issue that could be resolved by reflashing even if no updated software is available?

Related to PCM, does anyone know what the PCM update for those other vehicles actually does to calibration or system logic?


Thanks for any help!

I always thought pintle position was %, not voltage......

If it is not 0 % at idle, then you check for debris under pintle...if none, you replace the EGR....

If I remember right, there was a TSB years ago, about changing the EGR from a Delphi to a Siemans, due to a moisture problem.....you would think this would have been done by now.....I think the Sieman'* harness comes out of the EGR horizontally, while the Delphi came out vertically....

What I would want to do is look at EGR data that is captured when the code is set.......what you want to look at is what the TPS % is and what the EGR position % is....they should BOTH be ZERO! Or if you want to use voltage for a reference look to see if there is * voltage difference of 0.2 volts with the throttle closed.....

If your EGR connection comes out the side, then that is the Sieman'* EGR.....

Found this.....

Circuit Description
The PCM monitors the EGR valve pintle position input to ensure that the valve responds properly to commands from the PCM. When the ignition is turned on, the PCM learns the EGR closed valve pintle position. The PCM compares the learned EGR closed valve pintle position to the Actual EGR position when the EGR valve is commanded closed. If the Actual EGR position indicates that the EGR valve is still open when the PCM is commanding the EGR valve closed, DTC P1404 will set.

Conditions for Running the DTC
IAT is more than −10°C (14°F).
Engine run time is achieved. The length of time ranges from 20 seconds to 6 minutes depending upon engine coolant temperature at startup.
System voltage is between 10.0 volts and 18.0 volts.
Desired EGR must equal zero.
Conditions for Setting the DTC
EGR Feedback is 0.2 volt more than the EGR Closed Valve Pintle Position when the Desired EGR Position is commanded to 0 percent.
The above condition is present for longer than 20 seconds.
Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp (MIL) during the first trip in which the diagnostic test has been run and failed.
The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

Diagnostic Aids
Inspect for the following:

Inspect for excessive deposits on the EGR valve pintle or seat.
Remove the EGR valve and inspect for deposits that may interfere with the EGR valve pintle extending completely or cause the pintle to stick.
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important:: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

Loose terminal connection
Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections, and to Connector Repairs in Wiring Systems for diagnosis and repair.
Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections, and to Connector Repairs in Wiring Systems for diagnosis and repair.
Damaged harness—Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.
Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

Thanks for the ideas and input. I did not explicitly mention it, but I do have access to the diagnostic procedure, system theory, and other service info via AllData.

I'm not sure I'm following the thought process for including TPS in this. Throttle position values don't factor into triggering the P1404 from what I understand, although TP is of course helping to drive the PCM'* commands for desired EGR.

But to clarify, at idle (at a stop during a drive) the PCM is setting desired EGR = 0%. However, when that idle occurs after the vehicle is driven for a couple of minutes, the learned closed position has dropped below the initial .9V. So when desired EGR = 0%, the actual EGR position voltage (EGR feedback) drops to .9V as expected. But the PCM shows the calculated actual EGR position > 0% (and EGR error > 0%) because the PCM is basing those % calculations using EGR feedback (.9V) and the now-erroneous closed position voltage (which has become <.9V) -- if the difference between those two exceeds .2V, then P1404 can be triggered.

The diagnostic procedure doesn't discuss the case where the learned closed position is not holding constant. It only indirectly covers it at step 14, which is replace the PCM after all other values check ok. I think I'm still wondering if anyone has ever seen that value not staying constant and perhaps found a cause other than a bad PCM. I've seen other older threads where it seemed people couldn't find a cause for recurring P1404s even after replacing the EGR valve and re-learning the closed pintle position, and I'm wondering if they had a changing learned closed pintle position value and didn't know it.

Thanks for the ideas and input. I did not explicitly mention it, but I do have access to the diagnostic procedure, system theory, and other service info via AllData.

I'm not sure I'm following the thought process for including TPS in this. Throttle position values don't factor into triggering the P1404 from what I understand, although TP is of course helping to drive the PCM'* commands for desired EGR.

But to clarify, at idle (at a stop during a drive) the PCM is setting desired EGR = 0%. However, when that idle occurs after the vehicle is driven for a couple of minutes, the learned closed pintle position has dropped below the initial .9V. So when desired EGR = 0%, the actual EGR position voltage (EGR feedback) drops to .9V as expected because that is 0% for that valve. But the PCM shows the calculated actual EGR position > 0% (and EGR error > 0%) because the PCM is basing those % calculations using EGR feedback (.9V) and the now-erroneous closed position voltage (which is signifcantly <.9V) -- if the difference between those two exceeds .2V, then P1404 can be triggered.

The diagnostic procedure doesn't discuss the case where the learned closed position doesn't stay constant. The learned closed pintle position shouldn't be changing, right? The diagnostics only indirectly cover this case at step 14, which is replace the PCM after all other values check ok. I think I'm still wondering if anyone has ever seen that value not staying constant and perhaps found a cause other than a bad PCM.

I've seen other older threads where it seemed people couldn't find a cause for recurring P1404s even after replacing the EGR valve and re-learning the closed pintle position, and I'm wondering if they had a changing learned closed pintle position value and didn't know it.

Since this looks like an intermittent condition, I would check the female pins in the harness connector for tightness, and also for a bad wire in the harness....a wire could be broken inside the insulation, causing AN INTERMITTENT CONDITION, when the engine flexes in it'* mounts.....

Remember this code means anything that is in the circuit, can cause it, EGR, wiring, PCM/ECM, etc.

In rare cases, a partially plugged cat can create a back pressure, that can lift a pintle off it'* seat, causing a discrepancy in commanded and actual states...

In cases like this, I would have test driven the car with a Tech II in snapshot mode, and then check the data if the code triggered...

Well, the P1404 has appeared to be intermittent, and the PCM has even self-cleared the code and turned off the MIL, but after analyzing this in greater detail I think the apparent intermittent nature of the P1404 is the result of the particular trips being taken and their impact on the DTC logic. There are a lot of short 1 or 2 mile trips due to school pickups, errands, etc. that get taken in this vehicle. Given the conditions for running the DTC, and the fact that the PCM will clear the P1404 if 3 trips have passed where the DTC has run and passed, I think the nature of this vehicle'* driving is what led me to initially describe this as intermittent.

The PCM is probably not even running the DTC on many trips (especially now in winter) because the engine doesn't fully warm up. When the DTC does run, short trips are not setting it - in just a mile of driving, the learned closed pintle position hasn't dropped by the full .2V so the difference that exists is not enough to set the DTC. And if P1404 has already set, short trips will add up to get the 3 consecutive needed to clear it.

The manual says the P1404 will set on the first trip in which the diagnostic has run and failed, but I do question that. I am seeing P1404 pending (but MIL off) after a longer trip. The pending P1404 probably hasn't matured a lot of times due to subsequent short trips that are good.

What I am finding to be consistent is that the learned closed pintle position value drops on every trip. The degree to which it drops depends on trip duration. Shouldn't I be seeing the same value whether I'm 10 seconds into a trip or 10 minutes or 10 hours - or is there some legitimate reason why this stored value could change and drop mid-trip?

I understand your suggestion about a possible electrical/wiring issue causing an intermittent issue, but if I were to rewrite my initial problem description I would no longer call this intermittent. Whether or not the P1404 actually sets, the learned closed position value consistently drops. Our usual trips may or may not be long enough for it to drop at least .2V every time.

I'm not seeing any inconsistencies in the values for EGR feedback (they'd have to exist for at least 20 seconds so I should be able to recognize something out of whack) and I've never had a P0403 or P0405 indicating other issues with the circuits. From what I've seen, whenever desired EGR (commanded) = 0, EGR feedback (actual) = .9V which is the valve'* 0 (or closed) position.

I know this is an old thread, but I've performed the same diagnostics and reached the same conclusion. There is a TSB outlining a dealership PCM flash for my vehicle, but I'm wondering if OP was able to find a solution.

Thanks,
Snail

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