This bulletin applies to 2014-2020 Chevy Impala vehicles. The hood ajar message may be displayed when the hood is completely closed. The check engine light jay be on and DTC P257D (engine hood switch performance) may be set.
Inspect for coolant leaking from the coolant temperature sensor connector wicking up circuits 410 and 2761 from the coolant temp sensor to the ECM connector X3 at pins 7, 8, 23 and 24. This may cause a short across circuits 5350 and 470 at pins 7 and 23, which is the hood open switch signal and sensor low reference.
Disconnect the ECT sensor and inspect for internal coolant leakage. Trace the circuits back to te X3 connector at the ECM and inspect for coolant contamination/corrosion. If coolant corrosion or discoloration is found, replace circuits 410 and 2761 from the engine coolant temp sensor to ECM connector X3 at the ECM.
