P1690

P1690 on Hyundai/Kia is Immobilizer Lamp Circuit Malfunction — the body control module or engine ECU couldn't communicate with the immobilizer/transponder system, the dash lamp circuit shorted, or the transceiver coil around the ignition lock cylinder failed. This is an anti-theft fault: the car may start once and stall after 2-3 seconds (Hyundai's anti-theft startup-and-die behavior), or fail to crank at all. Cheapest-first ladder: scan with a scan tool that can talk to the SMARTRA/immobilizer module (cheap generic OBD scanners often can't read these) and check for related codes like B1670/B2799 alongside P1690. Try a known-good spare key — if the spare starts the car cleanly, the original key's transponder chip is dead and needs to be re-coded or replaced. Measure the transceiver coil (the ring antenna around the ignition cylinder) for continuity — typical spec is 1-3 ohms; an open coil means a new antenna ring. Inspect the dash immobilizer lamp circuit for a shorted bulb or LED driver. Don't go straight to ECM/SMARTRA replacement — these modules are $400-$900 and have to be coded to the VIN by a dealer or capable locksmith; the fault is usually a $30 transponder chip or a $80 antenna ring.

Vehicle-specific patterns: 2007-2012 Hyundai Elantra / Kia Forte with the Nu 2.0L is one of the most common P1690 platforms — the antenna ring inside the steering column fails from heat and vibration. 2006-2010 Sonata 2.4L Theta and 2011-2015 Sonata Theta II both throw P1690 from SMARTRA module failure after long-term battery drain events (a dead battery left for weeks can corrupt the SMARTRA pairing). 2010-2014 Kia Soul / Hyundai Accent / Kia Rio show P1690 from transponder chip failure in the key itself — common when the key has been dropped on a hard surface repeatedly. 2014+ vehicles with proximity smart-key (push-button start) throw P1690 less often, but when they do, the fix involves the smart-key control unit, not the column antenna. Estimated repair: $80 (transponder key DIY) to $700 (SMARTRA module + dealer coding).