P1633moderate severityPowertrain
Keep Alive Power Voltage Too Low
on 2021 Ford Mustang Mach-E Standard Range Dual Motor AWD · RWD
What this code means
The PCM has detected that the Keep Alive Power (KAPWR) voltage is too low. This immediately illuminates the MIL and means the PCM cannot maintain its adaptive learning values. The KAM circuit should maintain battery voltage at all times.
Symptoms
- Check Engine Light (immediately on)
- Engine may not start
- Poor idle quality
- Harsh transmission shifts
- Loss of all adaptive values
Common causes
- Corroded battery terminals or cables
- Faulty PCM power relay
- Blown KAM fuse
- Discharged battery
- Excessive parasitic draw depleting battery
- Wiring issue in KAPWR circuit
Diagnostic steps
- Check battery voltage (should be >12.4V key off)
- Inspect battery terminals for corrosion
- Check KAPWR fuse
- Test PCM power relay
- Test KAPWR circuit voltage at PCM connector
- Check for parasitic battery draw
Repair notes
Clean battery terminals. Replace KAPWR fuse. Replace battery if discharged. Repair wiring.
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