The P0624 code in your 2019 Buick Enclave indicates that the ECM has detected higher than expected voltage on the generator lamp L terminal control circuit. This is the opposite of P0623—instead of low voltage, the circuit shows elevated voltage that exceeds normal operating parameters.
High Voltage on the L Terminal
High voltage on the L terminal typically indicates the circuit isn't completing to ground properly. When the alternator is charging normally, the L terminal voltage should drop as current flows through the lamp circuit. If the circuit is open or has high resistance, voltage readings appear elevated because no current is flowing to pull the voltage down.
Common Causes
An open circuit in the L terminal wiring prevents proper current flow, resulting in high voltage readings. A failed indicator lamp (if traditional bulb type) opens the circuit. Disconnected or corroded connectors create high-resistance connections. Alternator internal issues, including a failed lamp driver or regulator problems, can cause this condition.
What This Means for Your Enclave
The charging indicator light may not illuminate during key-on (bulb check) or may never turn off regardless of charging status. Actual charging may function normally, but warning capability is compromised. The check engine light illuminates with P0624 stored.
Diagnostic Procedure
Using GM GDS2 or a compatible scanner, check L terminal voltage readings. With key on engine off, measure voltage at the L terminal—it should show a specific voltage indicating the lamp circuit is complete. Trace wiring for opens and high resistance. Check the instrument cluster for indicator lamp function. Inspect alternator connector and internal connections.