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DTC codes / U00xx · Network wiring and bus faults / U0037

U0037Vehicle Communication Bus B

U0037 is a generic network communication code indicating that the vehicle's communication bus B, a dedicated data link between control modules, has failed or is unreliable. The computer detected that messages expected on this bus are missing, corrupted, or that the bus voltage is outside its normal operating range, which prevents modules from sharing critical information.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaNetwork wiring and bus faults

Symptoms you may notice

  • Multiple warning lights illuminated simultaneously, often including the check engine light, ABS, and traction control
  • Intermittent or complete failure of dashboard gauges and warning indicators
  • The engine may start but run poorly or stall because the powertrain control module cannot receive sensor data from other modules
  • Transmission may default to limp mode or refuse to shift normally
  • Accessories such as power windows, radio, or climate control may operate erratically or not at all
  • Often no symptoms besides the warning light if the fault is intermittent and non-critical modules are affected

Common causes, most likely first

  1. Damaged or chafed wiring in the bus B harness, often where it passes through a door jamb or near a sharp metal edge
  2. Corroded or loose connector pins at any module attached to bus B, especially in areas exposed to moisture
  3. A failed control module that is shorting the bus B data lines to ground or power
  4. Open circuit in the bus B wiring caused by a broken wire or a disconnected inline connector
  5. Electrical interference from a failing alternator or ignition component that corrupts bus B signals
  6. Water intrusion into a module connector or harness splice pack that serves bus B
  7. A faulty termination resistor inside one of the modules on bus B, which upsets bus voltage levels

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes in every module to confirm U0037 is current and identify which modules are not communicating
  2. Inspect the bus B wiring and connectors at each module for corrosion, loose pins, or physical damage, starting with the modules that are offline
  3. Measure bus B voltage with a digital multimeter at the data link connector and compare it to the manufacturer's specification to check for a short or open
  4. Perform a resistance check across the bus B data lines to verify termination resistor integrity and rule out an open circuit
  5. Disconnect modules one at a time to see if bus communication returns, isolating a module that is shorting the bus
  6. Repair or replace the damaged section of harness or the faulty connector, then clear codes and verify communication with all modules
  7. If a module is confirmed faulty, replace and reprogram it according to the manufacturer's procedure, then road test to confirm the repair

What most technicians miss on bus B faults

  • A single failed module can bring down the entire bus B network, so disconnecting modules one by one is often faster than chasing wiring through the whole harness.
  • Bus B is frequently confused with the main high-speed CAN bus, but it may be a separate low-speed or dedicated network, so always consult the wiring diagram for the specific vehicle before probing.
  • Intermittent U0037 codes often set only when a particular accessory is used, such as a power seat or door lock, which points to a chafed wire in that circuit's harness.
  • Aftermarket electronics spliced into bus B wiring, such as alarm systems or dash cameras, are a common cause of communication faults that owners overlook.
  • A weak battery or failing alternator can cause bus B voltage to drop below the threshold for reliable communication, setting U0037 without any wiring fault at all.

Can I keep driving with U0037?

If the vehicle starts and runs normally, you can drive it cautiously to a repair shop, but avoid long trips and expect that other systems may behave unpredictably. If the engine stalls, the transmission will not shift, or multiple safety systems are disabled, stop driving and have the vehicle towed.

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 all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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