P1251
Manufacturer-specific Basic entry
Alternator Load Input Failed
Severity
Medium
Typical repair cost
40 – 350 EUR
System
Powertrain
This is a manufacturer-specific code. Its exact meaning can differ between makes; the definition below follows the most common usage.
What it means
P1251 is a general fault for the Alternator Load Input Failed circuit: the engine control module has detected a condition it cannot classify as low, high or open, often because the fault changes during the test.
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Symptoms
- Check engine light on
- Rough or unstable idle
- Hesitation or poor acceleration
- Increased fuel consumption
- Possible limp mode with reduced power
Common causes
- Damaged, chafed or corroded wiring in the Alternator Load Input Failed circuit
- Corroded, loose or water-damaged connector terminals
- Failed Alternator Load Input Failed component (sensor, solenoid or actuator)
- Poor ground connection for the module or component
- Faulty control module driver (rare, confirm all else first)
How to diagnose
- Read freeze frame data and note when the code set (cold start, under load, after rain)
- Inspect the Alternator Load Input Failed connector for bent pins, corrosion and water; wiggle the harness with the engine running and watch live data
- Measure supply voltage and ground at the connector with the key on
- Check the signal wire for shorts to ground or battery and for continuity to the control module
- Test or substitute the Alternator Load Input Failed only after wiring and connectors are confirmed good
- Clear the code and complete a drive cycle to confirm the repair
Frequently asked questions
Can I keep driving with P1251?
Usually yes for a short time, but expect reduced performance or higher fuel use. Have it diagnosed within a few days.
Will clearing P1251 fix it?
No. Clearing only erases the stored code; it returns as soon as the monitor runs again unless the cause is repaired.