Conditions for Clearing the MIL/DTC

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.

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.

DTC P0404

Step	Action	Values	Yes	No
Schematic Reference: Engine Controls Schematics or Emission Hose Routing Diagram 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	Start the engine. Using the EGR System Seal Output Control function, command the EGR Solenoid to 100 percent with the scan tool. Observe the EGR Vacuum Sensor parameter with a scan tool. Is the vacuum less than the specified value?	35 kPa	Go to Step 3	Go to Step 4
3	Observe the Freeze Frame/Failure Records for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition?	-	Go to Step 4	Go to Intermittent Conditions
4	Disconnect the vacuum line from the EGR vacuum sensor. Connect a vacuum gage to the vacuum line. Start the engine. Allow the engine to reach operating temperature. Using the EGR System Seal Output Control function, command the EGR Solenoid to 100 percent with a scan tool. Observe the vacuum gage. Does the vacuum measure more than the specified value?	15 in Hg	Go to Step 10	Go to Step 5
5	Turn OFF the engine. Disconnect the vacuum line from the vacuum pump. Install a vacuum gage on the vacuum pump with a short piece of vacuum line. Start the engine. Observe the vacuum gage. Does the vacuum measure more than the specified value?	15 in Hg	Go to Step 6	Go to Step 9
6	Test all of the EGR system vacuum lines for leaks and for restriction. Did you find and correct the condition?	-	Go to Step 12	Go to Step 7
7	Connect a hand held vacuum pump to the following components to determine if they can hold 15 Hg of vacuum for 30 seconds: The EGR valve vacuum diaphragm The EGR throttle valve vacuum diaphragm If a problem is found, refer to Exhaust Gas Recirculation (EGR) Valve Replacement or Air Intake Pipe Replacement . Did you find and correct the condition?	-	Go to Step 12	Go to Step 8
8	Connect a hand held vacuum pump to the following components to determine if they can hold 15 Hg of vacuum for 30 seconds: The EGR valve control solenoid The EGR throttle valve control solenoid If a problem is found, refer to Exhaust Gas Recirculation (EGR) Valve Solenoid Replacement or Exhaust Gas Recirculation (EGR) Valve Throttle Solenoid Replacement . Did you find and correct the condition?	-	Go to Step 12	Go to Step 11
9	Replace the vacuum pump. Refer to Exhaust Gas Recirculation (EGR) Valve Vacuum Pump Replacement . Did you complete the replacement?	-	Go to Step 12	-
10	Replace the EGR vacuum sensor. Refer to Exhaust Gas Recirculation (EGR) Valve Vacuum Sensor Replacement . Did you complete the replacement?	-	Go to Step 12	-
11	Replace the EGR vacuum vent solenoid. Refer to Exhaust Gas Recirculation (EGR) Valve Vent Solenoid Replacement . Did you complete the replacement?	-	Go to Step 12	-
12	Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition?	-	Go to Step 2	Go to Step 13
13	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