Check for the following,
Excessive deposits on the EGR valve pintle or seat. Remove the EGR valve and check for deposits that may interfere with the EGR valve pintle extending completely or cause the pintle to stick.
Poor connections at PCM or EGR valve. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Damaged harness. Inspect the wiring harness for damage. If the wiring appears to be OK, connect multi meter and check circuit continuity while moving connectors and wiring harnesses related to the EGR valve. A change in the meters display will indicate the location of the malfunction.
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