P2505

ECM/PCM Power Input Signal Low

P2505 is a generic OBD-II powertrain diagnostic trouble code: ECM/PCM Power Input Signal Low. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P2505
Group
Powertrain
System
Powertrain
Severity
Critical (limp mode / no-start)
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What P2505 means

P2505 is set when the ECM/PCM detects that its primary power supply input voltage is below the acceptable operating threshold. The module continuously monitors the voltage on its main power supply pins; when this voltage drops below a calibrated minimum, the code is stored to indicate inadequate supply to the control module itself. This is a fundamental electrical fault rather than a system-specific emission fault.

Low ECM supply voltage can result from a weak or failing battery, a high-resistance connection in the main power feed circuit (corroded fuse holders, loose battery terminals, degraded wiring), or a failing charging system that cannot maintain adequate voltage. In some architectures, the code may be set transiently during a low-voltage event such as a hard engine crank.

This fault can have wide-ranging effects on all engine management functions since every output and calculation depends on stable supply voltage. Misfire, incorrect fuel trim, sensor errors, and erratic transmission behaviour may all occur alongside P2505. Resolving the supply voltage issue is prerequisite to diagnosing any other concurrent codes reliably.

Common causes

Most-frequently reported root causes when P2505 is logged.

  • 1
    Discharged or internally failing battery providing insufficient voltage under load.
  • 2
    Corroded or loose battery terminals increasing resistance in the main supply path.
  • 3
    High-resistance main fuse, fuse holder, or fusible link in the ECM power feed.
  • 4
    Failing alternator unable to maintain charging voltage during engine operation.
  • 5
    Corroded or loose ECM power supply connector pins.
  • 6
    Damaged main wiring from the battery or PDC to the ECM with elevated resistance.
  • 7
    Faulty body control module or IPDM affecting switched power feeds to the ECM.

Symptoms drivers notice

MIL illuminated, possibly alongside multiple additional DTCs.
Hard start or no-start condition if voltage is very low.
Erratic or unresponsive engine management behaviour.
Possible transmission shift faults or ABS/stability system warnings if battery is severely discharged.
Scan tool may report communication errors with the ECM.

How to diagnose P2505

A typical diagnostic flow when this code is present.

  1. 1
    Record all DTCs; note that multiple codes may be present as secondary effects of the low-voltage condition.
  2. 2
    Measure battery voltage at rest (should be approximately 12.6 V fully charged) and under crank load.
  3. 3
    Inspect and clean battery terminals and ground straps; measure voltage drop across the main positive and ground circuits.
  4. 4
    Test the charging system output voltage at idle and with electrical load applied.
  5. 5
    Check the ECM main power and ground fuses, fusible links, and fuse holders for corrosion or high resistance.
  6. 6
    Inspect the ECM power supply connector for corroded pins or intermittent contact.
  7. 7
    Address any charging system or battery fault first, then recheck for remaining codes.

Vehicles where we've handled P2505

Platforms in our catalogue with confirmed P2505 coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Can P2505 be caused by a short-duration low-voltage event like a dead battery jump-start?

Yes. A very low battery voltage during cranking can transiently drop the ECM supply below threshold, setting P2505. If the battery and charging system are healthy, the code may not return after clearing.

Should I replace the ECM if P2505 is set?

Rarely. P2505 almost always reflects an external power supply issue. Rule out battery, charging system, and wiring faults before considering ECM replacement.

Can P2505 cause other codes to appear?

Yes. Low supply voltage corrupts sensor readings and module communication, generating numerous secondary codes. Always repair the supply fault first and recheck which codes remain.

What voltage range does the ECM typically require?

Most automotive ECMs operate correctly between approximately 9 V and 16 V. Below roughly 9 V, module operation becomes unreliable and P2505 may be set.

Disabling P2505 in software

RaceTune can permanently disable P2505 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

ECUs with a P2505 disable in our catalogue

Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.

  • Bosch EDC17C50 verified 1 software version

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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