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2016 Ram 1500 - ABS & Traction Control Lights On, U0121 Code

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Mike T. · rep 0 · May 22, 3:30 AM · 1 replies · solved · Question

Vehicle: 2016 Ram 1500 Outdoorsman 5.7L Hemi

Hey guys,

My 2016 Ram 1500 (Outdoorsman trim, 5.7L Hemi) just lit up my dashboard like a Christmas tree. The ABS light and the Traction Control light are both on. I used my scanner and pulled a U0121 code, which points to 'Lost Communication with Anti-Lock Brake System (ABS) Control Module'.

I've tried disconnecting the battery for 15 minutes to reset things, but the lights came right back on after starting. The brakes feel normal, no weird noises or anything, but I'm concerned about driving without ABS or traction control. What should I be looking for here? Could it be a bad sensor, or something more serious with the ABS module itself? I'm at about 110,000 miles.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:30 AM

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ClearTheCode admin answer:

The U0121 code, 'Lost Communication with Anti-Lock Brake System (ABS) Control Module,' is a critical diagnostic trouble code indicating that the Powertrain Control Module (PCM) or another control module is not receiving data from the ABS module. This will almost always trigger both the ABS and Traction Control lights.

Here's a breakdown of common causes and diagnostic steps:

  1. Faulty ABS Module:

    • Cause: The ABS control module itself can fail internally, leading to a loss of communication. This is a common point of failure, especially as vehicles age.
    • Action: If all other checks are clear, the ABS module is a strong suspect. A professional diagnostic tool can attempt to communicate directly with the ABS module. If it cannot, the module is likely faulty.

  2. Wiring and Connectors:

    • Cause: Damaged, corroded, or loose wiring and connectors between the ABS module and other vehicle systems (like the PCM or the CAN bus) can interrupt communication.
    • Action: Visually inspect the wiring harness leading to the ABS module for any signs of damage, fraying, or corrosion. Check the main connector to the ABS module for a secure fit and clean pins. A multimeter can be used to check for continuity and proper voltage/ground at the module's connector.

  3. Blown Fuse:

    • Cause: The ABS module requires power to operate. A blown fuse in the ABS circuit will cut power, resulting in a loss of communication.
    • Action: Check all fuses related to the ABS system in both the under-hood and interior fuse boxes. Refer to your owner's manual for the exact fuse locations and ratings.

  4. Wheel Speed Sensors (Indirect Cause):

    • Cause: While a direct wheel speed sensor fault usually triggers specific wheel speed sensor codes (e.g., C0031), a severe or multiple sensor failure could potentially confuse the ABS module to the point of causing a communication error, though this is less direct for a U0121.
    • Action: It's worth checking for any other related codes. If you have a scanner that can read live data, check the wheel speed sensor readings.

When to See a Shop: Because the ABS system is critical for vehicle safety, and diagnosing communication issues can be complex, it's highly recommended to take your Ram to a qualified mechanic or dealership. They have specialized diagnostic equipment that can communicate with individual modules, test wiring harnesses, and accurately pinpoint the root cause of the U0121 code, ensuring your braking system is fully functional and safe.

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