Powertrain, generic · Computer and auxiliary outputs

P0623 Generator Lamp Control Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P0623 concerns the control of the battery warning lamp by a module's output driver, not the alternator itself. Traditionally the regulator switches the lamp through terminal L; where a module switches it instead – GM's Saab 9-4X turns the lamp on 15 s after a charging code – it can monitor its lamp output for open or short circuits. No manufacturer document available to us uses P0623, so the description follows the principle of other lamp outputs. Under CARB a pure indicator lamp needs the check engine light only if other diagnostics depend on it, which is rarely the case. The lamp then never lights (not even at the bulb check) or stays on, and real charging faults may go unnoticed. The L line itself is P0621; the fuel cap lamp P0624 belongs to a different system.

Likely causes

Wire or connector to the lamp or instrument cluster
Bulb/LED or instrument cluster faulty
Output driver in the module
Ground fault

Symptoms

  • Battery lamp never lights (not even at bulb check) or stays on
  • Real charging faults may not be displayed
  • Otherwise usually no driving symptoms

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€30–400
Time0.5–2 h

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

Parts involved

battery warning lampinstrument clusterlamp control circuit

Related codes

P0620P0621P0622P0624

References: law.cornell.edu, saabwisonline.com, pmmonline.co.uk.