2023 Rivian R1T

Rivian R1T U0073 CAN Bus Off — Moisture in Underbody Gateway Module

U0073 U0100 U0121 Published 2025-05-06 Updated 2025-05-06
Rivian R1T U0073 CAN bus gateway moisture underbody communication

2023 Rivian R1T presented with multiple U-codes and random ADAS and powertrain communication faults after river crossing during off-road use. Water entered the underbody gateway module housing, causing CAN bus termination failure and widespread network communication faults.

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The Problem
2023 Rivian R1T Adventure (22,500 miles) presented after a controlled river crossing (approx 600mm depth) during an overlanding trip. After crossing, multiple warning lights appeared: lane keep, ACC, powertrain caution. U0073 (CAN Bus Off), U0100 (Lost Communication with BMS), U0121 (Lost Communication with ABS) stored.
Diagnostic Procedure
  1. 1. Confirm U-codes. All intermittent but U0073 most persistent — points to network-level fault rather than individual module failure.
  2. 2. CAN bus resistance test on chassis CAN. Normal should be 60 ohms (two 120-ohm termination resistors in parallel). Reads 38 ohms — lower than spec, indicating a third termination path (moisture bridging CAN H and CAN L inside a module).
  3. 3. Rivian R1T has an underbody gateway module mounted low on the left frame — specifically engineered for off-road but sealed to 600mm water wading depth only with a fully intact seal.
  4. 4. Remove underbody gateway cover. Visible moisture inside. Condensation on internal PCB. Two CAN termination resistors showing corrosion on solder joints.
  5. 5. Water entry point: rear seal on gateway housing shows a small crack — likely from a rock impact on the trail prior to the river crossing.
  6. 6. Dry module thoroughly with controlled heat (45°C for 4 hours). Treat corroded solder joints.
  7. 7. Replace gateway housing (seal kit). Reinstall.
  8. 8. CAN resistance: 61 ohms. All U-codes clear. ADAS and powertrain communication fully restored. No fault return on 50-mile test including water splash test.
Resolution & Root Cause
Underbody gateway module dried, corroded joints treated, housing seal replaced. CAN bus restored, all communication faults resolved.
💡 Key Lesson
Rivian R1T underbody gateway is rated to 600mm wading but requires an intact housing seal. Rock damage to the gateway housing before a water crossing eliminates the water protection. U0073 with a low CAN bus resistance (below 60 ohms) indicates moisture inside a module adding a parasitic termination. Measure resistance, identify the module, dry and reseal before condemning any control module.
About This Case

This case was solved remotely by an HVDesk specialist with 15+ years of hands-on experience across major EV platforms including Tesla, Hyundai/Kia, Volkswagen ID series, BMW i-series, and Ford EVs. The procedure was provided as structured remote support to an independent auto repair shop.