Powertrain, generic · Computer and auxiliary outputs

P0648 Immobilizer Lamp Control Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

The engine module switches this hard-wired output with its own driver and checks the circuit electrically (open, short to ground or voltage) – it cannot see whether the lamp lights; on CAN-based cars such faults appear as U codes. P0648 concerns the immobiliser or security lamp where the engine module drives it directly by wire – on GM and Saab systems this lamp shows the immobiliser learn mode and faults. No manufacturer document available to us uses this code; the description follows CARB and the component. The lamp then does not show the immobiliser status, or shows it permanently; the immobiliser itself keeps working, because start authorisation is separate (key faults are P0513/P0633). The immobiliser is not an emission component, so no check engine light is expected.

Likely causes

Wire or connector between module and receiver open, corroded or shorted
Bulb/LED or instrument cluster faulty
Instrument cluster (board, connector) faulty
Output driver in the module faulty

Symptoms

  • Immobiliser lamp off, permanently on or flashing wrongly
  • Code stored
  • Engine start normally not affected

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–400
Time0.5–2 h

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

Parts involved

immobilizer lampinstrument clusterlamp control circuit

Related codes

P0513P0633P0650P0649U0155

References: law.cornell.edu, saabwisonline.com.