Diagnostic Aids
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If DTC cannot be duplicated and is determined to be intermittent, reviewing freeze frame/failure records can be useful in determining when DTC was last set. Also, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.
A short to voltage in pump relay control circuit can result in AIR pump running continuously with ignition off by backfeeding to ground. This will eventually result in pump failure.
An AIR pump that had become inoperative and had shown indications of having exhaust gases in outlet port would indicates check valve failure.