P2509
ECM/PCM Power Input Signal Intermittent
The ECU detects sporadic interruptions of its supply voltage. The fault is set when supply drops below a threshold for short periods, often during cranking or due to a poor connection.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Poor battery cable connectionCommon
- Intermittent main relayPossible
- Connector with intermittent contact under vibrationLess likely
Parts involved
- ECU Power Supply
- Main Relay
- Battery Terminals
P2509 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.