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P1666 fault code: what it means

P1666: Engine anti-theft (immobiliser) signal circuit fault. The engine may not start.

Engine and gearbox (powertrain) · Costly if missed

Usual causes, most likely first

  1. immobiliser (BCU) fault
  2. wiring fault between BCU and ECM

P1666 by make

Land Rover

Engine anti-theft (immobiliser) signal circuit fault. The engine may not start.

Usual causes: immobiliser (BCU) fault; wiring fault between BCU and ECM

Not sure what P1666 means on your car? Ask Credov.

Before you clear it

Write the code down or photograph the scanner first. A code that comes straight back after clearing points to a fault that is still there. A car whose codes were cleared just before you arrived may be hiding one: the scanner's readiness monitors show "not ready" for a while after codes are cleared.

Researched by Credov from manufacturer and workshop sources. A fault code points to where a fault may be; a workshop confirms it with a diagnosis. Browse all fault codes.