U0149 indicates that a control module on the vehicle network has lost communication with a Gateway Module D. The gateway module acts as a router between different vehicle communication networks, and this code means the expected data exchange is not happening. It is a network/communication fault, not a direct engine performance code.
The gateway module itself has failed internally and is no longer transmitting or receiving network data. This is the most direct cause of a dedicated lost-communication code.
An open circuit, short to power/ground, or corroded/poor terminal contact on the serial data bus can prevent the gateway from communicating with other modules.
If the gateway module is missing battery voltage, ignition voltage, or ground due to a blown fuse, relay, or wiring fault, it will not power on and communication will be lost.
A shorted or failed module on the shared communication network can pull the bus down and cause a loss of communication with the gateway, even though the gateway itself is functional.
Extremely unlikely as a cause. The reporting module would only be the source if its own transceiver circuit has failed, which is rare. Investigate all other causes first.
It depends on the symptoms. If the vehicle starts and drives normally and no safety-critical systems are affected, limited driving may be possible. However, because this is a communication fault, certain subsystems may be in a default or inoperative state, so diagnosis should not be delayed.
No. Replacing the PCM/ECM is almost never the correct fix for U0149. The code indicates a loss of communication with a gateway module, and the root cause is far more commonly a wiring fault, power/ground issue, or the gateway module itself. The PCM should be considered only after every other possibility has been definitively ruled out.
Because the gateway module routes data between networks, a failure of the gateway or a disruption on its bus can cause multiple modules to report lost communication. The presence of several U-codes often points to a shared network problem rather than each module being individually faulty.
No. U0149 is a network communication code, not an emissions code. It will not cause a vehicle to fail an emissions test on its own, though it may illuminate a warning lamp depending on the vehicle.