Is It Safe to Drive With a P2504 Code?
Common Symptoms of a P2504 Fault
P2504 Symptoms at a Glance
Battery warning light
EML on
Electrical components failing
Bulbs blowing
Battery overcharging
Possible Causes of P2504
A P2504 code can be triggered by faults across several systems. Identifying the exact root cause requires proper diagnostic equipment and live data — not just reading the code.
Common Causes of P2504
Alternator Voltage Regulator Failure
Voltage regulator in alternator failed causing overcharging.
Charging Circuit Fault
Wiring fault causing voltage to rise.
Battery Monitoring Fault
Battery sensor giving incorrect readings.
ECU Charging Control Fault
ECU not correctly controlling alternator output.
Why we don't list the exact part: A P2504 code tells you what's happening but not why. Replacing parts based on the code alone is the most common way drivers waste money. A proper diagnosis identifies the specific cause first.
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P2504 and Your MOT
A stored P2504 fault code will cause your car to fail its MOT. The engine management light will be illuminated during the test — an automatic failure under current MOT standards. Even if the light temporarily clears, the code remains in ECU memory and can be read by testers.
Get the fault diagnosed and repaired first, then have the code cleared and confirm the light stays off before booking your MOT.