P0452 code set. on 1999 Chevrolet 1500 Pickup

MIL on code PO452 set. Clear with scan tool and it resets immediately. Evap sensor replaced with fuel pump, no better. What needs to be done next.

Asked by for the 1999 Chevrolet 1500 Pickup
clearing code never fixes it. you need a diag from a shop that knows what to look for. you need a scanner tool, vaccuum pump, meter and voltage source to properly test to find defective part

what is code452.and what should i look for