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DTC codes / Chrysler codes / P1518

P1518 · ChryslerThrottle Actuator Control (TAC) Module Serial Data Circuit

P1518 on Chrysler vehicles means the Throttle Actuator Control (TAC) module has lost or corrupted the serial data circuit it uses to communicate with the Powertrain Control Module (PCM). The PCM sets this code when it detects a missing, intermittent, or invalid message from the TAC module over the dedicated serial data line, so the fault is in the communication path rather than in the throttle motor or pedal sensor itself.

SystemPowertrain
Code typeChrysler specific
SeverityHigh
Fix difficultyProfessional
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • The electronic throttle control warning light or the check engine light illuminates steadily.
  • The engine may enter limp-home mode with limited power and a maximum engine speed of about 1,500 rpm.
  • The accelerator pedal may feel unresponsive or delayed when pressed.
  • In some cases the engine may crank but fail to start because the PCM refuses to authorize throttle operation.
  • Often no symptoms besides the warning light, especially if the serial data fault is intermittent.
  • A stored P1518 may be accompanied by other throttle actuator codes such as P2135 or P2100.

Common causes, most likely first

  1. Damaged, chafed, or corroded wiring in the TAC module serial data circuit between the TAC module and the PCM.
  2. Loose or contaminated connector terminals at the TAC module or PCM, often caused by water intrusion or road salt.
  3. A failed TAC module that no longer transmits or receives serial data reliably.
  4. A faulty PCM that cannot process the serial data message, though this is less common than wiring faults.
  5. Poor ground connection at the TAC module or PCM, which corrupts the serial data signal.
  6. Aftermarket electronic throttle controllers or piggyback tuners that splice into the serial data line and disturb the signal.
  7. Battery voltage irregularities or a weak battery that causes the TAC module to drop offline intermittently.

How to diagnose and fix it

  1. Scan all modules for stored codes and record freeze-frame data to confirm P1518 is active and not a historical ghost code.
  2. Inspect the TAC module and PCM connectors for corrosion, pushed pins, or loose terminals, and clean or repair as needed.
  3. Perform a voltage drop and continuity test on the serial data circuit between the TAC module and the PCM, wiggling the harness to catch intermittent faults.
  4. Check the TAC module and PCM ground circuits for excessive resistance and repair any corroded ground points.
  5. If wiring and grounds are good, substitute a known-good TAC module and clear the code to see whether it returns.
  6. Verify battery condition and charging system output, since low voltage can cause the TAC module to drop serial communication.
  7. After repairs, clear codes and perform a throttle relearn or idle relearn procedure with a scan tool, then road test to confirm the code does not reset.

What the serial data circuit really means

  • P1518 is a communication code, not a throttle motor or pedal sensor code, so replacing the throttle body or accelerator pedal assembly without testing the serial data line is a common and expensive misdiagnosis.
  • The TAC module serial data circuit is a dedicated low-speed data line, and a single chafed wire behind the engine or near the pedal assembly can set this code intermittently without any driveability complaint.
  • Water intrusion into the TAC module connector, often from a clogged cowl drain or a missing connector seal, is a frequent cause on older Chrysler vehicles and is easily overlooked during a visual inspection.
  • Aftermarket remote starters, alarm systems, or throttle controllers that tap into the serial data line can corrupt the signal and set P1518 even though the factory wiring is intact.
  • A weak or failing battery can cause the TAC module to reset mid-drive, setting P1518 along with other communication codes, so always check charging system health before condemning the module.

Can I keep driving with P1518?

Do not continue driving normally when P1518 is active, because the vehicle may enter limp-home mode without warning and lose throttle response in traffic. If the engine starts and idles, drive only a short distance to a safe repair location at low speed, and avoid highways or heavy traffic until the fault is repaired.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Chrysler vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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