Chrysler SKIM Anti-Theft System (Sentry Key)

SKIM operates as a three-component system: the Sentry Key (transponder chip in the key), the SKIM module (usually mounted to the ignition housing and containing the antenna ring coil), and the PCM (Powertrain Control Module). The authentication sequence at startup is a three-way handshake: 1. Key insertion: the SKIM module's antenna ring energizes the Sentry Key's transponder chip at 125 kHz. 2. Key response: the Sentry Key chip transmits its rolling-code response back to the SKIM module. 3. SKIM-to-PCM authorization: the SKIM module, having validated the key response, sends an encrypted authorization message to the PCM over the vehicle's serial data bus (typically the PCI bus on older Chryslers, CAN bus on 2007+ vehicles). 4. PCM decision: the PCM receives and validates the SKIM authorization. Only with a valid authorization does the PCM enable fuel injector pulses and ignition coil firing. This architecture means the PCM itself never communicates with the key -- it relies entirely on the SKIM module for key validation. If the SKIM module is removed and a bypass is attempted at the PCM's authorization input, the PCM detects the absence of valid SKIM communication and continues to prevent engine running.

Programming a Sentry Key to a SKIM module requires the SKIM's unique security PIN. This PIN is a four-character hex code stored in the SKIM module's EEPROM memory, generated at the factory and unique to each module. To program a new key, the technician must provide this PIN to the programming tool, which then establishes a programming session with the SKIM module and instructs it to add the new transponder chip's ID to its authorized list. The SKIM PIN can be obtained in several ways: from the vehicle's original documentation (some dealers provide the PIN with the vehicle at purchase), from a Chrysler dealer with access to the SKIM PIN database (obtainable via VIN from Stellantis's dealer portal), or extracted directly from the SKIM module via OBD-II using a professional programmer with appropriate access (Autel, AVDI, Lonsdor, etc.) or via EEPROM read of the module's memory chip. All-keys-lost for SKIM vehicles follows the same PIN approach: the PIN is obtained or extracted, the programming tool establishes a secure session with the SKIM module, and new keys are enrolled. The SKIM module can typically hold up to 8 Sentry Key IDs in its memory. During AKL programming, the technician can optionally erase all previously enrolled keys and enroll only the new ones, effectively invalidating any lost or stolen keys.

SKIM failures manifest as engine crank-and-die sequences (similar to other immobilizer failures) accompanied by specific warning indicators. The 'SENTRY KEY' indicator light (or padlock icon on newer vehicles) illuminates and flashes a coded sequence indicating the specific fault. Common SKIM fault codes accessible via scan tool include: P1684 (battery disconnect detected within last 50 engine starts -- informational), P1685 (invalid key or unprogrammed key in ignition), P1686 (SKIM module communication fault with PCM), P1687 (no SKIM bus message), B1003 through B2xxx range codes for SKIM module internal faults, and P0513 (invalid SKIM key -- most common). Antenna ring failure is a frequent SKIM failure mode on Chrysler products. The antenna ring is pressed over the ignition cylinder and held by two clips; it contains a coiled wire and small circuit board. Physical impacts to the steering column, heavy key chains that put lateral force on the ignition, or water intrusion from a sunroof or cabin leak can damage the antenna ring wiring. A broken antenna ring presents as P0513 with a valid, enrolled key -- the key is fine, but the SKIM module cannot read it because the antenna field is absent.

The 2019 Ram 1500 (DT platform) and 2020 Jeep Grand Cherokee L introduced the Hitag AES transponder chip to the Chrysler product line. This is a quantum leap in security over the previous Philips 46 chips. Hitag AES uses 128-bit AES symmetric encryption with a dynamic rolling counter, making brute-force attacks computationally infeasible and clone attacks impossible. Programming Hitag AES keys requires a programmer with active AES key calculation capability (Autel IM608 Pro with relevant token package, AVDI with AES module, or equivalent). The programming session involves a seed-key exchange where the programmer requests a seed from the SKIM module, sends it to an online calculation server for the AES response derivation, and returns the response to the SKIM module to authenticate the programming session. Without active internet access to a valid calculation server, Hitag AES programming is not possible with any commercial tool currently available -- emphasizing why professional, properly licensed programming equipment is required for these vehicles.