U0140 — Lost Communication with Body Control Module (BCM)

What it means

U0140 is a generic network DTC (second digit 0) that indicates one or more controllers stopped receiving the required messages from the Body Control Module (BCM). On many platforms the BCM sits on the body network (e.g., Ford MS-CAN ~125 kbps or GM Low-Speed GMLAN single-wire ~33.3 kbps) and may also act as a gateway to HS-CAN (~500 kbps) where the ECM/PCM, TCM, ABS/EBCM, EPAS/PSCM, IPC/cluster live. Which module logs U0140 varies by OEM—e.g., Ford shows TPMS, ABS, RFA, PAM setting U0140 when BCM messages are missing. In short: a supervising node or gateway timed out waiting for BCM data. Charm+3OBD-Codes.com+3Charm+3

Typical symptoms

  • Warning lamps/messages (security/anti-theft, TPMS, ABS/ESC, “Service” or body-system messages)
  • Loss of body functions: power locks/windows, exterior lighting logic, keyless entry/remote start, wipers, interior lighting, horn, etc.
  • Scan tool shows U-codes across several modules; BCM offline or intermittently not enumerating on the network/topology map
  • In some cases: no-start/crank-no-start if the BCM is part of the immobilizer/gateway path. RepairPal.com+1

Why it sets (representative OEM logic)

  • Message timeout from BCM. Controllers that depend on BCM data (e.g., TPMS, ABS, RFA, PAM, IPC) set U0140 when required BCM status frames are not received within calibrated timers (“Missing Message” / “No Subtype Info” variants appear in OEM charts). Charm+2Charm+2
  • Network/physical-layer degradation. Opens/shorts, termination faults, or a noisy/failed node drive up error rates so BCM frames aren’t delivered. GM HS-LAN guidance anchors diagnostics with ≈60 Ω ±5 Ω total at rest on HS-CAN (two 120-Ω ends in parallel) and structured isolation of branches. (Low-speed body networks have different physical layers/expectations.) NHTSA
  • OEM nuance (GM). PIT4730B documents intermittent “BCM offline” cases where all other HS-GMLAN modules still communicate during that ignition cycle—illustrating that U0140 can be a transient gateway/body-bus issue rather than a hard HS-CAN failure. NHTSA

Common root causes

  1. Power/ground loss at the BCM (blown fuse, poor ground, low system voltage)
  2. Body-network wiring faults (opens/shorts, corroded splices/connectors; door/rocker/A-pillar harnesses)
  3. Gateway or termination issues (esp. on platforms where BCM is a gateway between body CAN and HS-CAN)
  4. Connector pin tension/corrosion; water intrusion at BCM or junction blocks
  5. Internal BCM/transceiver failure causing intermittent error-passive/bus-off behavior
  6. Aftermarket device interference (remote starts, alarms, trackers, audio/telemetics) tied into body or HS networks. RepairPal.com+1

Professional diagnostics (step-by-step)

Network overview & scan strategy

  • Run a global scan. Note every U-code and which modules are offline. Use the scan tool’s topology/gateway map to see if the BCM is enumerating and which network it rides on (MS-CAN/Low-Speed vs HS-CAN). On Ford, you’ll often see TPMS/ABS/RFA logging U0140 when BCM messages are missing. Charm+1

Power/ground checks at the BCM

  • Verify B+, IGN, and grounds under load at the BCM (target ground drop ≤100–200 mV). A powered-down BCM looks like a network failure to the rest of the car. Correct battery/charging/ground issues first. RepairPal.com

Bus integrity tests (match the physical layer)

  • HS-CAN (if BCM/gateway has HS legs): Key-off ≈60 Ω ±5 Ω across CAN-H/CAN-L; key-on at rest ~2.5 V common-mode with small/ opposite deviations on H/L. Abnormal resistance/voltage suggests open/short or termination faults; proceed with branch isolation per OEM HS-LAN procedure. NHTSA
  • Low-Speed body nets: Expect different specs. Ford MS-CAN is two-wire (~125 kbps) with 60-Ω pair checks at the correct splice/connector (often not at DLC). GM Low-Speed GMLAN is single-wire (~33.3 kbps) (no “60 Ω pair” check); evaluate for clean 0–5 V signaling and proper load/termination per OEM. (Use platform SI while testing.) RepairPal.com

Segment isolation

  • If the BCM is intermittently offline while other modules communicate, follow OEM isolation steps: depower/unplug branches at junction blocks or pull fuses to sub-nets while watching when communications recover. PIT4730B specifically addresses intermittent BCM offline behavior during an ignition cycle. NHTSA

Connector/terminal inspection

  • Perform pin-drag tests at the BCM and nearby junctions; look for backed-out pins, water/corrosion, poor splices, and chafe in door/rocker/A-pillar runs. Repair and restore proper twist/routing where applicable. RepairPal.com

Aftermarket device audit

  • Temporarily remove alarms/remote starts/trackers/DLC dongles tied into body or HS networks and retest. Many lost-comms clusters trace to add-ons. RepairPal.com

Module actions (last)

  • Only after wiring, network integrity, and power/grounds are proven: apply software updates if available; then replace/initialize the BCM or gateway per OEM programming requirements. (Some platforms require PATS/immobilizer parameter resets and key relearns.) RepairPal.com

Verified fixes

  • Restore BCM power/grounds; correct low-voltage and ground-eyelet issues
  • Repair body-network wiring and splices; clean/repin connectors; seal water ingress paths
  • Resolve termination/gateway faults; correct star-point/junction issues
  • Remove/rewire interfering aftermarket devices
  • Reflash when calibration updates address network robustness; replace/initialize BCM only after proving the network healthy
  • Clear codes, drive cycle, and re-scan to confirm. NHTSA+1

Sources

  • OBD-Codes – U0140 (Lost Communication with Body Control Module) — generic definition and detection-time example. OBD-Codes.com
  • Ford OEM service (charm.li mirrors) — U0140 set by TPMS/ABS/RFA/PAM when BCM messages are missing (“:00 No Subtype” / “:87 Missing Message”). Charm+2Charm+2
  • GM/ACDelco via NHTSA — “Diagnosing High-Speed LAN Concerns” — OEM HS-CAN resistance (≈60 Ω) and isolation strategy. NHTSA
  • GM PIT4730B (2017) — Diagnostic Tip for U0140 or U0073; intermittent “BCM offline” behavior and ignition-cycle nuance. NHTSA
  • RepairPal — U0140 — plain-language overview; BCM role and gateway context for body features. RepairPal.com