Powertrain, generic (extended)

P2502 Charging System Voltage

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P2502 is the general charging-system code: the engine module compares the voltage the generator actually delivers with what it has requested and finds a mismatch that it does not classify as simply too low or too high. Mazda uses it as a malfunction in the voltage produced by the generator. On 2022–2023 Mazda2 mild hybrids built in Mexico the charge lamp came on while driving; Mazda traced it to resistance at the ground terminal of the DC-DC converter under heavy current and replaced the converter with revised software. Ford lists P2502 for the 2014 BOSS 302S module. CARB lets makers pause other monitors at low or high system voltage, which is why charging faults matter for the OBD system. Directional faults are P2503 and P2504.

Likely causes

Alternator or regulator not reaching the requested voltage
High resistance at ground or B+ connections (Mazda mild hybrid DC-DC converter)
Slipping drive belt or worn tensioner
Battery with internal fault distorting the charging voltage

Symptoms

  • Charge warning lamp on while driving
  • Fluctuating battery voltage, flickering lights
  • Battery not fully charged

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–900
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

alternatorvoltage regulatorbattery

Related codes

P2503P2504P0620P0562

References: static.nhtsa.gov, performanceparts.ford.com, law.cornell.edu.