P1686 — No SKIM Bus Message Received

Causes

• SKIM module failure or no power/ground to SKIM module
• Open, shorted or damaged SKIM data/communication wiring or connectors
• Blown fuse supplying SKIM or related modules
• Weak or low vehicle battery voltage during cranking or module wake-up
• Faulty ignition key transponder or key not learned to vehicle
• PCM/BCM or other gateway module communication fault

Symptoms

• Engine will not crank or will crank but not start
• Security/immobilizer or KEY/PRNDL indicator lamp illuminated or flashing
• No SKIM-related messages in scan tool module list or SKIM not responding
• Intermittent start problems
• DTC P1686 stored in PCM/ECM

What to check

• Verify vehicle battery voltage is within specification (12.4–12.8 V at rest). Recharge or load-test battery if low.
• Use a factory-level scan tool to read PCM, SKIM, BCM and any security module DTCs and modules present on the network.
• Check for blown fuses supplying SKIM, PCM and BCM (consult fuse chart).
• Inspect SKIM, PCM and BCM connectors for corrosion, bent pins, or water intrusion.
• Verify ground connections for SKIM, PCM and chassis/body grounds are clean and tight.
• Attempt to communicate with the SKIM module using scan tool; note any communication errors.

Signal parameters

• SKIM/immobilizer bus: periodic serial data messages expected from SKIM to PCM/BCM when ignition/key present (message frequency and IDs are vehicle-specific).
• Expected: SKIM module should appear on module list and respond to scanner requests; no response = communication fault.
• Battery voltage should remain above ~12 V during key-on and crank for reliable module communication (exact threshold varies by model).
• Security lamp status: lamp should flash during system check and extinguish when key recognized (behavior varies by model).

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