P2508: Ford internal ECU five-volt supply is too high

P2508 is broadly titled ECM/PCM power input signal high. Ford's 2015 diesel monitor gives it a precise internal context: the ECU's five-volt supply is above 5.5 volts. That threshold must not be applied to the vehicle's battery or alternator output.

Internal supply versus external charging voltage

The controller must be energized, which can include key-on, engine running or the post-drive interval before shutdown. The monitor is continuous and has a typical five-second duration. A fault recorded after engine shutdown can therefore still fit the published operating context.

The neighboring P2507 entry checks the low side of the same internal supply. Other reference-supply codes in the table monitor distinct sensor supplies, so their thresholds and circuit identities should not be merged with P2508.

Bound the diagnostic conclusion

Preserve when the event occurred and any other supply or controller faults. The source identifies an internal monitored condition but does not provide a component-level repair verdict or an external terminal where 5.5 volts should be measured. Use the correct ECU power and internal-fault diagnostic procedure. Do not open the controller or condemn the charging system solely because the generic code title contains power input high.

Source and applicability

Ford 2015 model-year diesel OBD system operation summary, revision December 22, 2014; the cited monitor only, without blanket model or engine applicability. Ford source, physical PDF pages 151, 152, 153. The documented monitor explains the fault decision; vehicle-specific service information is still needed for connector identification and a complete repair procedure.