I have an 02 chevy impala with the 3400 engine in it, approx 6 months ago the check engine light came on, I went to the local auto parts and they pulled up the code P0401 which is ( insufficent Egr flow ) Unfortunitly I was not able to correct the problem at the time and drove the car for the past six months in that condition. I now have the extra funds to fix this problem and at first checked and cleaned the EGR valve which in my opinion was not that carboned up and the plunger was working properly at least by my working it by hand, After cleaning it and also the port on the manifold which again was not to dirty IMHO, I put the original EGR valve back on and had the code erased,within 1 mile of driving the check engine light came back on with the same code. I was able to replace the original EGR valve with a new one and again had the code erased and still within 1 mile the check engine light came back on with the same P0401 code, so even with a new EGR valve it came back on, This system is run electronically and there are no vaccume lines to crack,break, etc,really not that much to it at all, but now is beyond my ability to check it out due to lack of proper test equipment and knowledge,So guys, anyone out there in BITOG land have any idea's as to what could be the problem now, The EGR valve itself has been checked,cleaned,and replaced and still the problem exist, any and all thoughts are greatly welcomed..thanks,KKAT
Having problem with EGR code
- Thread starter kkat
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Is there a sensor for the EGR flow? If so, check that.
there should be a flow sensor...ill see if i can find the specs for it at work today
A lot of times the computer checks for flow by monitoring engine vacuum, it expects to see a certain change when the EGR is open, and if it doesn't, it knows there's not enough flow. The MAP sensor could be the issue, but the next thing I'd do is check the wiring and connections for the EGR valve, you could have a problem there, too.
Last edited:
Many of these newer cars have sensors that need to be calibrated in order for them to function at 100% capacity. If this is one of those, you may have thrown the calibration off when you cleaned it. Call your dealer. They should be able to give you details.
I have this same motor in my 97 silhouette and also have issues. It runs the egr diagnostic coasting foot-off-the-gas down from 50 mph to 20 mph. Who does this? Have also heard of MAP sensor involved in diagnosing this.
One test is to remove the valve and start the car! It should have a really lousy idle, fast, or stalling, b/c of the vacuum leak, and you should hear exhaust.
One test is to remove the valve and start the car! It should have a really lousy idle, fast, or stalling, b/c of the vacuum leak, and you should hear exhaust.
Are you sure there is an actual flow sensor? On the vehicles I have worked on they will pop this code anytime the EGR plunger doesn't move when commanded but don't actually have a way to measure the flow. This can happen when the vacuum or electric solenoid doesn't function OR if the sensor on the EGR doesn't register motion correctly. If it is an all electric system I'd use a multimeter to check all the sensor and the actuator for signs of life.
I was able to replace the old EGR valve with a new one, and as stated I did not think the old valve was bad after looking at it and cleaning it somewhat, but a new valve was offered to me in which I could return it if that was not the problem, so That was an offer I could not refuse. still acting the same way even with the new valve installed, The only SOLENIOD/RELAY that I can see that might have to do with the EGR system would be the A.I.R.( AIR INDUCTION REACTION RELAY) the other relays/soenoids have to do with ac,compressor,fans,and the rest are fuses which are ok.I cleaned all the electric connections,and also the MAF sensor with the correct spray, Testing the electrical is a little above my abilities, Oh give me back the style vehicles where you could sit in the engine compartment and work on them. where are the vacumme lines and all the mechanical mechanism's.
The AIR system is something else, so don't fiddle with that 
.
What is it that actually moves the EGR valve to open it? Does it have a vacuum connection or is there an electric solenoid?
.What is it that actually moves the EGR valve to open it? Does it have a vacuum connection or is there an electric solenoid?
no vacuum connections at all, everything is electronic that runs the EGR
Originally Posted By: kkat
no vacuum connections at all, everything is electronic that runs the EGR
Double check all the electrical connections, making sure that the wires are good and none of the pins have pulled out the back of the plugs. Did you inspect the tube that comes from the exhaust to make sure it is clear and not full of carbon? If that doesn't work I think you may need to have another mechanic look at it. Either the pintle position sensor or the motor is not working and you'll need a multimeter to figure out which.
no vacuum connections at all, everything is electronic that runs the EGR
Double check all the electrical connections, making sure that the wires are good and none of the pins have pulled out the back of the plugs. Did you inspect the tube that comes from the exhaust to make sure it is clear and not full of carbon? If that doesn't work I think you may need to have another mechanic look at it. Either the pintle position sensor or the motor is not working and you'll need a multimeter to figure out which.
The car's computer self tests the EGR.
It puts it on at various times to sense the reaction, s well as normal monitoring.
So..
A port TO or FROM the EGR may be partially blocked, and the valve itself is not totally exonerated, at this point.
It puts it on at various times to sense the reaction, s well as normal monitoring.
So..
A port TO or FROM the EGR may be partially blocked, and the valve itself is not totally exonerated, at this point.
Here you go straight from GM. Cut&paste doesn't do much here but you can atleast read most of it. PM me and I can email you the actual documents.
xTooltipElement
Service Information
2002 Chevrolet Impala | Impala, Monte Carlo (VIN W) Service Manual | Document ID: 791913
--------------------------------------------------------------------------------
DTC P0401
Circuit Description
The powertrain control module (PCM) tests the exhaust gas regulation (EGR) system during deceleration by momentarily commanding the EGR valve to open while monitoring the manifold absolute pressure (MAP) sensor signal. When the EGR valve is opened, the PCM should see a proportional increase in MAP. If the expected increase in MAP is not seen, the PCM notes the amount of error that was detected and adjusts an internal fail counter towards a fail threshold level. When the fail counter exceeds the fail threshold level, the PCM will set this diagnostic trouble code (DTC). The number of test samples required to accomplish this may vary according to the amount of detected flow error.
Normally, the PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, the PCM allows twelve test samples during the first ignition cycle following a scan tool Clear Info or a battery disconnect. Between nine and twelve samples should be sufficient for the PCM to determine adequate EGR flow and pass the EGR test.
Conditions for Running the DTC
• DTCs P0101-P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121-P0123, P0201-P0206, P0300, P0336, P0403, P0404, P0502, P0503, P0506, P0507, P1106, P1107, P1111, P1112, P1114, P1115, P1121, P1122, P1374, or P1404 are not set.
• The system voltage is between 10-18 volts.
• The AC status does not change.
• The transaxle range does not change.
• The throttle position (TP) angle is less than 1 percent, deceleration.
• The intake air temperature (IAT) is more than 80°C (176°F).
• The engine coolant temperature (ECT) is more than 75°C (167°F).
• The engine speed is between 1,050-1,400 RPM.
• The idle air control (IAC) position is steady.
• The manifold absolute pressure (MAP) is steady between 15-70 kPa.
• The vehicle speed is more than 48 km/h (30 mph) during deceleration.
• The barometric pressure (BARO) sensor is more than 70 kPa.
• The vehicle will need to be driven faster 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 test to run. As the test is running, you will see the Desired EGR parameter and the EGR position sensor on the scan tool change from 0 to a calibrated value above 0.
Conditions for Setting the DTC
The MAP changes monitored during the EGR flow test indicate insufficient 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
Important: Inspect for the following conditions:
• Vacuum restriction to the MAP sensor--A restriction to the MAP sensor can cause the EGR flow test to fail due to insufficient MAP changes being monitored during the test. Inspect for objects blocking the vacuum to the MAP sensor.
• A poorly running engine--An engine that is running poorly may cause this DTC to set.
• A poor connection or a damaged harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the EGR Position Sensor display on the scan tool while moving connectors and wiring harnesses related to the EGR valve. A change in the display indicates the location of the malfunction.
In order to verify a repair, clear info with the scan tool and run the EGR flow test keeping the following conditions in mind:
• The PCM will only run the EGR flow test during a gradual deceleration.
• The PCM will only run the EGR test during a closed throttle condition.
• The PCM will only run the EGR test at vehicle speeds above 48 km/h (30 mph).
• Several deceleration cycles, typically 9-12, will be necessary to run a sufficient number of EGR flow test samples.
• The EGR Test Counter displayed on the scan tool can be useful in determining that the EGR flow test is running and in order to keep track of the number of test samples taken. The counter will increment each time a test sample is taken.
Test Description
The number below refers to the step number on the diagnostic table.
This DTC is set when the PCM does not detect a predetermined change in MAP when the EGR valve is commanded. This step checks for any MAP sensor DTCs. A malfunctioning MAP sensor may cause this DTC to set.
Step
Action
Yes
No
Schematic Reference: Engine Controls Schematics
1
Did you perform the Diagnostic System Check-Engine Controls?
Go to Step 2
Go to Diagnostic System Check - Engine Controls
2
Is there any MAP DTCs set?
Go to Diagnostic Trouble Code (DTC) List
Go to Step 3
3
Inspect the exhaust system for modification of original installed parts or leaks.
Repair the exhaust system as necessary if you locate a problem.
Did you find and correct the condition?
Go to Step 7
Go to Step 4
4
Inspect the EGR valve gasket and pipe for leaks.
If you locate a problem, clean or replace the EGR system components as necessary. Refer to Exhaust Gas Recirculation (EGR) System Cleaning .
Did you find and correct the condition?
Go to Step 7
Go to Step 5
5
Remove the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .
Inspect the following components for leaks or for restrictions:
• The EGR pintle
• The EGR valve passages
Did you find and correct the condition?
Go to Step 7
Go to Step 6
6
Remove the EGR inlet pipe from the exhaust manifold. Refer to Exhaust Gas Recirculation Pipe Replacement .
Inspect the manifold EGR ports and the EGR inlet pipe for a blockage caused by excessive deposits or other damage.
Did you find and correct the condition?
Go to Step 7
Go to Diagnostic Aids
7
Use the scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass ?
Go to Step 8
Go to Step 2
8
With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?
Go to Diagnostic Trouble Code (DTC) List
System OK
© 2009 General Motors Corporation. All rights reserved.
xTooltipElement
Service Information
2002 Chevrolet Impala | Impala, Monte Carlo (VIN W) Service Manual | Document ID: 791913
--------------------------------------------------------------------------------
DTC P0401
Circuit Description
The powertrain control module (PCM) tests the exhaust gas regulation (EGR) system during deceleration by momentarily commanding the EGR valve to open while monitoring the manifold absolute pressure (MAP) sensor signal. When the EGR valve is opened, the PCM should see a proportional increase in MAP. If the expected increase in MAP is not seen, the PCM notes the amount of error that was detected and adjusts an internal fail counter towards a fail threshold level. When the fail counter exceeds the fail threshold level, the PCM will set this diagnostic trouble code (DTC). The number of test samples required to accomplish this may vary according to the amount of detected flow error.
Normally, the PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, the PCM allows twelve test samples during the first ignition cycle following a scan tool Clear Info or a battery disconnect. Between nine and twelve samples should be sufficient for the PCM to determine adequate EGR flow and pass the EGR test.
Conditions for Running the DTC
• DTCs P0101-P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121-P0123, P0201-P0206, P0300, P0336, P0403, P0404, P0502, P0503, P0506, P0507, P1106, P1107, P1111, P1112, P1114, P1115, P1121, P1122, P1374, or P1404 are not set.
• The system voltage is between 10-18 volts.
• The AC status does not change.
• The transaxle range does not change.
• The throttle position (TP) angle is less than 1 percent, deceleration.
• The intake air temperature (IAT) is more than 80°C (176°F).
• The engine coolant temperature (ECT) is more than 75°C (167°F).
• The engine speed is between 1,050-1,400 RPM.
• The idle air control (IAC) position is steady.
• The manifold absolute pressure (MAP) is steady between 15-70 kPa.
• The vehicle speed is more than 48 km/h (30 mph) during deceleration.
• The barometric pressure (BARO) sensor is more than 70 kPa.
• The vehicle will need to be driven faster 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 test to run. As the test is running, you will see the Desired EGR parameter and the EGR position sensor on the scan tool change from 0 to a calibrated value above 0.
Conditions for Setting the DTC
The MAP changes monitored during the EGR flow test indicate insufficient 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
Important: Inspect for the following conditions:
• Vacuum restriction to the MAP sensor--A restriction to the MAP sensor can cause the EGR flow test to fail due to insufficient MAP changes being monitored during the test. Inspect for objects blocking the vacuum to the MAP sensor.
• A poorly running engine--An engine that is running poorly may cause this DTC to set.
• A poor connection or a damaged harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the EGR Position Sensor display on the scan tool while moving connectors and wiring harnesses related to the EGR valve. A change in the display indicates the location of the malfunction.
In order to verify a repair, clear info with the scan tool and run the EGR flow test keeping the following conditions in mind:
• The PCM will only run the EGR flow test during a gradual deceleration.
• The PCM will only run the EGR test during a closed throttle condition.
• The PCM will only run the EGR test at vehicle speeds above 48 km/h (30 mph).
• Several deceleration cycles, typically 9-12, will be necessary to run a sufficient number of EGR flow test samples.
• The EGR Test Counter displayed on the scan tool can be useful in determining that the EGR flow test is running and in order to keep track of the number of test samples taken. The counter will increment each time a test sample is taken.
Test Description
The number below refers to the step number on the diagnostic table.
This DTC is set when the PCM does not detect a predetermined change in MAP when the EGR valve is commanded. This step checks for any MAP sensor DTCs. A malfunctioning MAP sensor may cause this DTC to set.
Step
Action
Yes
No
Schematic Reference: Engine Controls Schematics
1
Did you perform the Diagnostic System Check-Engine Controls?
Go to Step 2
Go to Diagnostic System Check - Engine Controls
2
Is there any MAP DTCs set?
Go to Diagnostic Trouble Code (DTC) List
Go to Step 3
3
Inspect the exhaust system for modification of original installed parts or leaks.
Repair the exhaust system as necessary if you locate a problem.
Did you find and correct the condition?
Go to Step 7
Go to Step 4
4
Inspect the EGR valve gasket and pipe for leaks.
If you locate a problem, clean or replace the EGR system components as necessary. Refer to Exhaust Gas Recirculation (EGR) System Cleaning .
Did you find and correct the condition?
Go to Step 7
Go to Step 5
5
Remove the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .
Inspect the following components for leaks or for restrictions:
• The EGR pintle
• The EGR valve passages
Did you find and correct the condition?
Go to Step 7
Go to Step 6
6
Remove the EGR inlet pipe from the exhaust manifold. Refer to Exhaust Gas Recirculation Pipe Replacement .
Inspect the manifold EGR ports and the EGR inlet pipe for a blockage caused by excessive deposits or other damage.
Did you find and correct the condition?
Go to Step 7
Go to Diagnostic Aids
7
Use the scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass ?
Go to Step 8
Go to Step 2
8
With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?
Go to Diagnostic Trouble Code (DTC) List
System OK
© 2009 General Motors Corporation. All rights reserved.
Another think to do is remove the throttle body,the passage for the EGR is possibly plugged right up with carbon.I have seen this with a 2001 Lumina,had this code and the EGR passage was plugged right up with carbon.
I can't add much to what has already been posted. I'd make DANM sure that the egr passage in the intake and the pipe coming from the exhaust manifold are open... I still suspect that that's your problem.
I think you've pretty much ruled out the valve as a the problem, seeings how it still threw the code with a replacement valve.
Wiring is always a possibility- I'm not familiar enough with GM codes to say for sure, but I would THINK that there would be a separate code for the EGR circuit itself if that was the problem.
Like others have said, the ECM will partially open the EGR valve during normal driving and watch for a corresponding drop in manifold vacuum as a way of self-testing EGR flow. So, as other folks suggested, I reckon a MAP sensor problem COULD be the culprit. I've seen MAP sensors 'stick'- so that they'll give a signal that's within range (and therefore will not necessarily throw a code), but the reading doesn't change with vacuum. It'll generally make the car run like $hit... but that might not necessarily be the case on a vehicle like yours that also has a MAF sensor.
Does the car run ok?
I think you've pretty much ruled out the valve as a the problem, seeings how it still threw the code with a replacement valve.
Wiring is always a possibility- I'm not familiar enough with GM codes to say for sure, but I would THINK that there would be a separate code for the EGR circuit itself if that was the problem.
Like others have said, the ECM will partially open the EGR valve during normal driving and watch for a corresponding drop in manifold vacuum as a way of self-testing EGR flow. So, as other folks suggested, I reckon a MAP sensor problem COULD be the culprit. I've seen MAP sensors 'stick'- so that they'll give a signal that's within range (and therefore will not necessarily throw a code), but the reading doesn't change with vacuum. It'll generally make the car run like $hit... but that might not necessarily be the case on a vehicle like yours that also has a MAF sensor.
Does the car run ok?
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