P1638

DTC P1638 (76): MCM Internal Circuit Malfunction
1. Reset the MCM.
2. Turn the ignition switch OFF.
3. Turn the ignition switch ON (II).
Is DTC P1638 indicated?
YES-Update the MCM if it does not have the latest software, or substitute a known-good MCM, then recheck. If the symptom/indication goes away with a known-good MCM, replace the original MCM.
NO-Intermittent failure, system is OK at this time.