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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1044 (Engine Controls Diagnosis - 6.6L (Lb7) (DTCS P0237 To P0611)) >> Diagnosis >> DTC P0401 >> Diagnostic Aids

Diagnostic Aids

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Inspect the MAF sensor for proper operation. An inaccurate MAF sensor signal may cause this DTC to set. Refer to Scan Tool Data List

If the condition is determined to be intermittent, refer to Intermittent Conditions .

DTC P0401

Step Action Value(s) Yes No
Schematic Reference: Engine Controls Schematics
Connector End View Reference:  Engine Control Module (ECM) Connector End Views  or  Engine Controls Connector End Views 
1 Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2 Is DTC P0404, P0405, P0406, P0489, P0490, P1404, P2141, P2142, P2144, or P2145 also set? - Go to Diagnostic Trouble Code (DTC) List Go to Step 3 
3
  1. Disconnect the exhaust gas recirculation (EGR) valve vacuum hose.
  2. Install a vacuum gage on the vacuum hose.
  3. Start and idle the engine.
  4. Command the EGR System Seal to 100 percent with a scan tool.
Is the vacuum more than the specified value?		 15 in Hg Go to Step 4  Go to Step 7 
4
  1. Connect a vacuum pump to the EGR valve.
  2. Apply 15 inches of Hg.
Does the EGR valve hold steady vacuum?		 - Go to Step 5  Go to Step 8 
5
  1. Connect a vacuum pump to the EGR throttle valve vacuum diaphragm.
  2. Apply 15 Hg.
Does the EGR throttle valve vacuum diaphragm hold steady vacuum?		 - Go to Step 6  Go to Step 8 
6 Test for the following conditions:
  • Restricted or leaking vacuum hose between the vacuum pump and the EGR throttle valve vacuum diaphragm.
  • A restricted or leaking EGR throttle valve vacuum control solenoid.
  • A sticking EGR throttle valve.
  • Plugged EGR ports-Refer to Exhaust Gas Recirculation (EGR) System Cleaning .
  • Exhaust system leaks.
  • Exhaust system restrictions.
  • Exhaust system modifications.

Did you find and correct the condition?		 - Go to Step 10  Go to Diagnostic Aids
7 Repair the leak or restriction in the vacuum hose between the EGR valve and the vacuum sensor.
Did you complete the repair?		 - Go to Step 10  -
8 Replace the EGR throttle valve vacuum diaphragm. Refer to Air Intake Pipe Replacement in Engine Mechanical.
Did you complete the replacement?		 - Go to Step 10  -
9 Replace the EGR valve. Refer to Exhaust Gas Recirculation (EGR) Valve Replacement .
Did you complete the replacement?		 - Go to Step 10  -
10
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds
  3. Start the engine.
  4. Operate the vehicle with in the Conditions for Running the DTC. You may also operate the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?		 - Go to Step 2  Go to Step 11 
11 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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