U0107

U0107 is a generic OBD-II diagnostic trouble code indicating a lost or no communication with the engine control module (ECM) or powertrain control module (PCM) over the vehicle’s data network, typically the CAN bus. The code is defined under the U (network) category and is commonly described as “Lost Communication with ECM/PCM ‘Internal Control Module’ – Bus A” though exact wording can vary by vehicle.

Cause and scope

The code is usually triggered when the vehicle’s network cannot exchange data between the ECM/PCM and one or more other control modules. Common causes include a faulty ECM/PCM or other connected module, damaged or corroded wiring and connectors, blown fuses or poor power and ground supply, battery voltage irregularities, recently replaced or reflashed control units, or loose connections. Because modern vehicles rely on multiple modules communicating over CAN or similar networks, a problem anywhere on the bus can set U0107.

Symptoms

A vehicle displaying U0107 may have the check engine light illuminated, and related vehicle systems (transmission, anti-lock braking, body control, or infotainment) may show intermittent behavior due to lost data. Some vehicles may run normally until prompted to exchange data with the ECM/PCM, at which point problems become evident.

Diagnostic and repair approaches

Diagnosis typically begins with a scan for all stored and pending codes and then inspection of the CAN (or other bus) network wiring, connectors, and power/ground supplies to the ECM/PCM and related modules. Check fuses, battery condition, and voltage stability. Verify termination resistors and inspect for damaged insulation, pin corrosion, or bent pins. If wiring and power are sound, the issue may reside in a faulty ECM/PCM or another module, which may require replacement, reprogramming, or software updates followed by code clearing and a road test to confirm resolution.

See also: OBD-II codes, CAN bus, vehicle diagnostics.