Low Voltage at Engine Control Module (ECM) Power Supply
Indicates low voltage detected at the ECM power supply.
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What it means (plain English)
The ECM isn't getting enough voltage, likely below 10 volts, which means it's not working correctly. Think of it like a phone not charging properly; if the battery is low, it won't operate as it should.
What the computer is actually seeing
The ECM expects a steady voltage supply between 10 to 16 volts for normal operation. When it reads below that threshold, it triggers the SPN 1690 code.
What a healthy reading looks like
ECM power supply should be between 10 to 16 volts during engine operation and at least 12 volts with the key on, engine off.
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.
- 11. Start by checking the battery voltage; should be 12.6 volts or higher with the engine off.
- 22. If voltage is low, check the battery condition and connections for corrosion or looseness. Repair as necessary.
- 33. With the engine running, check the voltage at the ECM power supply terminal; it should be between 13.5 to 14.5 volts. If not, proceed to the next step.
- 44. Inspect the wiring harness and connectors from the battery to the ECM for any damage or shorts. Repair any found issues.
- 55. Test the alternator output; should produce at least 13.5 volts. If the output is low, replace the alternator.
Common causes
- Bad battery connection or corrosion on terminals
- Faulty alternator not providing adequate charge
- Damaged wiring or connectors in the ECM power supply circuit
- Weak battery not holding proper voltage under load
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's not recommended to drive with this code as it can cause engine performance issues.
Will this problem come back after I fix it?
If the underlying electrical issues are not resolved, it is likely to return.
Why does this code pair with others?
Related codes may indicate similar electrical or grounding problems affecting the ECM.
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