Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
- The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
- Commanding the EGR valve open determines whether the EGR system is totally restricted or partially restricted.
- Visually and physically inspect the EGR passages and valve for excessive carbon deposits or damage.
- Be sure all gasket material is removed from the EGR mounting surface. Even a small amount of material may cause a DTC P0401 to set.
- This step verifies if the fault is present and also verifies if a repair corrected the problem. If the EGR Deceleration Filter value stays near 0 or a positive number after several tests have been run, then a small restriction may still exist. Be sure to check the EGR pipe for damage or dents and the EGR valve for any excessive carbon build up. Only 1 test per ignition cycle will run unless a DTC P0401 has been cleared or the battery has been disconnected.
- Clearing DTCs is a very important step for this diagnostic. The clearing function allows the EGR valve to relearn a new pintle position as the old pintle position was inaccurate due to the failure that caused the DTC. The DTC must be cleared with the ignition ON, engine OFF or when the engine is idling. If the ECM sees a EGR command, the new pintle will not be learned.