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P0623 Generic (SAE) Basic entry

Generator Lamp Control Circuit

Updated 2026-10-02 · Computer & output circuits

Severity
Low
Typical repair cost
60 – 500 EUR
System
Powertrain

What it means

P0623 is defined as "Generator Lamp Control Circuit". the engine control module stores it when the monitored condition for this component or system is outside the limits programmed by the manufacturer.

This entry is compiled automatically from the standard definition and typical diagnostic practice for this type of fault. A detailed, reviewed article is in preparation.

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Symptoms

  • Check engine light on
  • Engine may not start or runs in limp mode
  • Several unrelated codes stored at once
  • Erratic gauge or warning light behaviour

Common causes

  1. Generator Lamp Control Circuit worn, contaminated or out of calibration
  2. Mechanical problem in the system the sensor measures
  3. Air, vacuum or exhaust leak influencing the reading
  4. Wrong or low-quality replacement part
  5. Wiring resistance causing a small voltage offset

How to diagnose

  1. Compare the live Generator Lamp Control Circuit reading with a known-good value or a second sensor at idle and at 2500 rpm
  2. Check for air, vacuum or exhaust leaks that could skew the reading
  3. Inspect the component for contamination and clean it if the design allows
  4. Verify the part number is correct for the engine
  5. Replace the Generator Lamp Control Circuit if the reading remains out of specification

Frequently asked questions

Can I keep driving with P0623?

Yes. The fault does not affect safety or driveability, but it will keep the warning light on and may fail an inspection.

Will clearing P0623 fix it?

No. Clearing only erases the stored code; it returns as soon as the monitor runs again unless the cause is repaired.

Related codes

P0621P0622P0624P0625

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