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Home / DTC / B2797 — Transponder Key Antenna Circuit Malfunction

B2797 — Transponder Key Antenna Circuit Malfunction

Detailed page for trouble code B2797.

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Code

B2797

Generic B — Body

Transponder Key Antenna Circuit Malfunction

Brand: Generic
Type: B — Body
Views: UK: 10 EN: 9 RU: 6
AI status
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Page language: EN

Causes

  • Damaged or open antenna coil (for transponder/key detection)
  • Broken, shorted or corroded wiring or connector to the antenna
  • Poor or missing power supply or ground to the antenna/reader
  • Faulty immobilizer / body control module or antenna driver circuit
  • Faulty or non-programmed key/transponder
  • Interference from aftermarket alarms, stereo, or shielding

Symptoms

  • Key not recognized or intermittent recognition
  • No-start or engine disabled by security system
  • Security/immobilizer indicator lamp stays on or flashes
  • Unable to program or re-learn keys
  • Intermittent faults that clear then return
  • Push-button start unresponsive if transponder not detected

What to check

  • Read all stored codes and freeze-frame data with a scan tool; note related body or communication codes
  • Visually inspect antenna, connector(s), wiring harness, and nearby components for damage or corrosion
  • Check fuses and chassis ground points related to the immobilizer/antenna circuit
  • Verify key battery and try a known-good programmed key
  • Measure supply voltage to the antenna connector with ignition ON
  • Check continuity/resistance of antenna coil and wiring to the immobilizer module

Signal parameters

  • Supply voltage: battery voltage (~12 V) present at antenna power feed with ignition ON (verify exact circuit in manufacturer's manual)
  • Ground: good low-resistance chassis ground at antenna/reader connector
  • Antenna coil resistance: manufacturer-specific; typically a low-ohm value (tens to a few hundred ohms) — compare to service spec
  • RF detection frequency: transponder systems commonly use ~125 kHz low-frequency carrier (check OEM spec)
  • Data: low-frequency modulation/pulses when a valid transponder is present; may be observed with a scope or specialized tester
  • CAN/serial: immobilizer module should communicate on vehicle bus; loss of comm can accompany antenna faults

Diagnostic algorithm

  1. Retrieve current and historic DTCs and freeze-frame; note any related body or communication codes.
  2. Confirm symptom with vehicle: attempt start with each key and observe security lamp behavior.
  3. Inspect fuse(s), antenna connector, and harness for corrosion, damage, or water ingress; repair as needed.
  4. Verify power and ground at the antenna/reader connector with ignition ON; if missing, trace and repair supply or ground.
  5. Measure antenna coil resistance and continuity to the immobilizer/BCM; compare to service spec. Replace coil/antenna if open or out-of-spec.
  6. Use an oscilloscope or dedicated transponder/antenna tester to check for LF carrier and modulation when key is present; if absent, suspect driver or wiring.
  7. Wiggle test harness and connectors while monitoring for code set to find intermittent faults.
  8. If wiring and antenna check OK, check immobilizer/BCM communications and outputs; swap with known-good module only if supported and after proper security procedures.
  9. Consider interference sources: test after disconnecting aftermarket devices that could affect LF signals.
  10. After repair or replacement, clear codes and verify proper key recognition and no return of fault; perform key re-learn if required.

Likely causes

  • Open or high-resistance antenna coil
  • Loose/corroded connector at the antenna or immobilizer module
  • Missing 12 V supply or poor ground to the antenna circuit
  • Intermittent wiring short to chassis or other circuits
  • Failed immobilizer/BCM driver for the antenna

Fault status

⚠️ Status
Transponder key antenna circuit malfunction detected. Check antenna coil, wiring, power/ground, and immobilizer module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3 hours

Similar codes

B2796 B2798 B2799 B2780 B2835
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