P2506
ECM/PCM Power Input Signal Range/Performance
The switched-battery input to the ECM/PCM is present, but the level or transient behaviour is out of plausibility — sagging during cranking, slow ramp-up after main-relay close, or noisy. Often caused by aged main relay contacts or a weak battery feed under load.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Aged main relay contacts with rising contact resistanceCommon
- Weak battery sagging during crankPossible
- Sensor element aged beyond calibration windowLess likely
Parts involved
- Main Relay
- Power Distribution
- Battery Cables
P2506 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.