DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient. Buick Century (China) 2000

For 1990-2009 cars only

Makes 🢒 Buick 🢒 2000 🢒 Century (China) 🢒 Engine 🢒 Engine Controls - 2.5L (LB8) and 3.0L (L46) 🢒 DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient

Engine Controls Components
HO2S, EGR and PCM (NF2 Only)
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Powertrain Control Module (PCM) tests the exhaust gas recirculation (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 DTC P0401. 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

•	No TP, MAP, MAF, ECT, IAT, CKP sensor, VSS, injector circuit, Misfire, Idle speed, EGR Pintle Position, DTCs set

•	The AC status does not change.

•	The transaxle range does not change.

•	The TP angle is less than 1 percent (deceleration).

•	The ECT is more than 75°C (167°F).

•	The engine speed is between 1000 RPM and 1250 RPM.

•	The IAC position is steady.

•	MAP steady between 15 and 70 kPa

•	Vehicle speed is more than 40 km/h (25 mph) during deceleration.

•	BARO sensor more than 70 kPa

•

The vehicle will need to be driven above 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. When the test runs, you will see the desired EGR parameter and the actual EGR position on the scan tool change from 0 to a calibrated value above 0.

Conditions for Setting the DTC

The MAP changes monitored during EGR flow test indicate insufficient EGR flow.

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.

Conditions for Clearing the MIL/DTC

•	The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.

•	The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

•	The DTC can be cleared by using a scan tool.

Diagnostic Aids

Notice: If the EGR valve shows signs of excessive heat, inspect the exhaust system for blockage--possibly a plugged converter--using the procedure found on the Restricted Exhaust System Check. If the exhaust system is restricted, repair the cause. Inspect for an open injector caused by one or more of the following conditions:

•

Stuck

•	Grounded driver circuit

•	Possible faulty control module

If one of the above conditions is found, inspect the oil for possible fuel contamination.

To verify a repair, clear info with the scan tool and run the EGR flow test, keeping the following items 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 will be necessary to run a sufficient number of EGR flow test samples (9-12).

•	The EGR Test Counter displayed on the scan tool can be useful in determining that the EGR flow test is running and to keep track of the number of test samples taken. The counter will increment each time a test sample is taken.

Inspect for the following conditions:

•

Poor connection or damaged harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the Actual EGR Position display on the scan tool while moving connectors and wiring harnesses related to the EGR valve. A change in the display will indicate the location of the fault. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

•	Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Step

Action

Values

Yes

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Inspect the exhaust system for modification of original installed parts or leaks.
If a problem was found, repair exhaust system as necessary.

Was a condition present that required repair?

Go to Step 5

Go to Step 3

Remove the EGR valve.
Visually and physically inspect the following items:

•	Pintle, valve passages and the adapter for excessive deposits or any kind of a restriction

•	EGR valve gasket and pipes for leaks

If a problem is found, clean or replace EGR system components as necessary.

Was a condition present that required repair?

Go to Step 5

Go to Step 4

Remove the EGR inlet and outlet pipes from the exhaust manifold and the intake manifold.
Inspect the manifold EGR ports and the EGR inlet and outlet pipes for a blockage caused by excessive deposits, casting, flashing or other damage.
If a problem is found, correct the condition as necessary.

Was a condition present that required repair?

Go to Step 5

Go to Diagnostic Aids

Review and record the scan tool Failure Records data.
Clear the DTC and monitor the EGR Test Count display on the scan tool while operating the vehicle as specified in Diagnostic Aids.
Continue operating the vehicle EGR Test Count until 9-12 test samples have been taken.
Select the scan tool Specific DTC information for DTC P0401and note test result.

Does the scan tool indicate DTC P0401 test Ran and Passed?

System OK

Go to Step 2