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P1245

Alternator Load Input Failed Low.

  • Other
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
2
AreaFuel and air metering (injector circuit)
45
FaultThe specific fault in that area

What it means

P1245 is a manufacturer-specific code, and its meaning differs between makes. On the definition used here, 'Alternator Load Input Failed Low', the engine control unit monitors a load signal from the alternator or its regulator and saw it stay below the expected range. The control unit uses this signal to adjust idle speed and torque as electrical load changes. Confirm the manufacturer's definition for the exact vehicle before diagnosing.

Symptoms

  • Charging system or battery warning light on
  • Idle speed unstable, hunting or dipping when electrical loads are switched on
  • Engine stalling or near-stalling at idle
  • Flat or weak battery
  • Dim headlights or sluggish electrical accessories
  • Engine management light on with no other obvious symptom

Possible causes

  • Open circuit, short to ground or poor connection in the alternator load signal wire between the alternator and control unitlikely
  • Corroded, loose or damaged alternator connector or terminalslikely
  • Faulty alternator or internal regulator not sending the load signal correctlylikely
  • Low battery voltage or poor earth and power connections affecting the signal referencepossible
  • Worn or slipping drive belt or a failing alternator pulley reducing outputpossible
  • Fault inside the engine control unit input circuitrare
  • Outdated control unit software, where the manufacturer has issued a fix for this faultrare

How to diagnose

  1. Confirm the vehicle make, model and engine, and check the manufacturer's definition of P1245 for it
  2. Read freeze frame data and any other stored codes, especially charging, battery voltage or idle control faults
  3. Check battery condition and resting voltage, then charging voltage at idle and with loads on
  4. Inspect the alternator connector, wiring loom and earth straps for damage, corrosion, chafing or heat damage
  5. Check the drive belt condition, tension and pulley operation
  6. Using the wiring diagram, test the load signal wire for continuity, short to ground and short to supply between the alternator and control unit
  7. With a scope or suitable meter, check that the alternator load signal changes as electrical loads are switched on and off
  8. Check for relevant software updates or technical bulletins for the model before condemning the control unit

How to fix

  • Repair or replace damaged wiring and fix any open circuit or short to ground in the load signal circuit
  • Clean, repair or replace corroded or loose connectors and terminals, and restore good earth connections
  • Replace the alternator or regulator if the signal or charging output is faulty
  • Charge or replace a weak battery once the cause of the low charge is found
  • Replace or retension a worn drive belt or faulty pulley
  • Update the control unit software only if the manufacturer lists this as a fix, and replace the unit only if the fault is confirmed in it

Can I keep driving?

Medium severity

Short journeys are usually possible, but the charging system may be failing and the battery could go flat, causing stalling or loss of electrical systems. Get it checked soon and avoid long trips or heavy electrical loads until then.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

This code for other makes

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