P2506: Engine Control Module Power Input Signal Range/Performance
What to do
Expect intermittent oddities rather than a consistent fault — occasional rough running, warning lights that come and go, sometimes a stall. Ask specifically for a voltage drop test under load on the module's supply and earths, not just a continuity check. A corroded joint passes continuity and still sags whenever something switches on, which is exactly what this code describes.
What this code means
The module's supply is present but not within the range it expects, or not behaving as it should under changing load.
The distinction that matters is between continuity and quality. A supply can be perfectly continuous and still be poor: a corroded joint or an undersized repair adds resistance, and resistance only shows itself when current is drawn. So a circuit that passes a continuity test can sag whenever the fuel pump, the fans or the injectors switch on.
That is why the measurement to ask for is a voltage drop under load rather than a continuity check. It is a different test with different equipment, it takes longer, and it is the one that finds these. A workshop reporting the circuit as good on a continuity test has not disproved this code.
Likely causes
Start here
- High resistance in the module supply · moderate
- Corroded earth connection · moderate
- Failing battery · easy
Less common
- Failed ECM power relay · easy
- Faulty alternator · moderate
- Corroded battery terminals · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
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