MCM/ECM Power Supply Voltage Out of Range
The engine control module detected a power supply voltage issue.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The engine control module (ECM) isn't getting the right voltage it needs to work properly. It should see around 12 volts, but it's either too high or too low, causing it to throw this code.
What the computer is actually seeing
The ECM is monitoring its own power supply voltage. If it sees a voltage below 9 volts or above 16 volts, it will set this fault code.
What a healthy reading looks like
Normal voltage range for the ECM should be between 9 to 16 volts.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check battery voltage with a multimeter; it should read between 12.4 to 12.8 volts (engine off). If not, replace the battery.
- 2Inspect the alternator output while the engine is running; it should be between 13.5 to 14.5 volts. If it's out of range, check alternator or charging system.
- 3Examine all connections and wiring to the ECM for corrosion or damage. Clean or repair as needed.
- 4If battery and alternator are good and wiring is intact, swap ECM with a known good unit to eliminate ECM failure.
Common causes
- Bad battery
- Faulty alternator
- Corroded or loose connections
- Damaged wiring harness
- Faulty ECM or MCM
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's not recommended to drive long distances until diagnosed, as it can lead to engine performance issues.
Will this code come back after clearing?
If the underlying issue is not resolved, the code will likely return after clearing.
Why does this code paired with SPN 100 sometimes?
SPN 100 indicates a generic data communication fault, often caused by poor power supply to the ECM leading to erratic behavior.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
Start guided diagnostic →