P2509

ECM/PCM Power Input Signal Intermittent

Q: Is it safe to drive with P2509?

Not reliably — losing power to the ECM can stall the engine without warning or leave you stranded. Have it diagnosed before depending on the car.

Q: Can I just clear P2509?

Clearing it won't fix the intermittent power or ground fault; it will return, often alongside other codes, until the connection is repaired.

Powertrain control (ECM power) Generic OBD-II High

What it means

P2509 means the engine control module is seeing its own power supply drop out or fluctuate intermittently. Because the ECM runs the engine, unstable power can cause stalling, hard starting, or a no-start, and often sets several other codes at once. The usual culprits are the battery, grounds, power relay, or corroded wiring.

High

Can I keep driving? Risky — the engine computer is losing power intermittently, which can cause sudden stalling, hard starting, or no-start. Diagnose before relying on the vehicle.

Real-world scan data

Seen in

scans in the past year

Found in

<0.1%

of scans

<0.1%

of scans that found faults

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

Common symptoms

What you'll notice

Check-engine light on
Intermittent stalling or the engine cutting out
Hard starting or no-start
Erratic running and multiple unrelated codes setting together
ECM resets losing learned settings (idle, adaptations)

Common causes

Most likely first

Weak or failing battery, or loose/corroded battery terminalsLikely
Poor engine or chassis ground connectionCommon
Faulty ECM power relay or a loose/blown power fuseCommon
Open, chafed, or intermittent wiring in the ECM power feedLess often
Faulty ECM (less common)Less often

How to diagnose & fix

Work through it in order

Load-test the battery and clean/tighten both battery terminals.
Inspect and clean the main engine and chassis ground straps.
Check the ECM power relay, fuses, and their sockets for looseness or corrosion.
Back-probe ECM power and ground pins and wiggle-test the harness for voltage dropouts.
Repair the wiring or connection found; replace the ECM only after power and grounds are confirmed good.

FAQ

Quick answers

Is it safe to drive with P2509?+

Not reliably — losing power to the ECM can stall the engine without warning or leave you stranded. Have it diagnosed before depending on the car.

Can I just clear P2509?+

Clearing it won't fix the intermittent power or ground fault; it will return, often alongside other codes, until the connection is repaired.

Read & clear P2509 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX