Code U0604 indicates a loss of communication between the vehicle's primary control module and a secondary fuel pressure sensor (Sensor B) on the Controller Area Network (CAN) bus. This specific code suggests the network is active, but the designated sensor is not responding to data requests. The issue typically stems from a faulty sensor, wiring defects, or network configuration errors rather than a failure of the main engine computer.
The internal electronics of the sensor itself have failed, preventing it from transmitting data onto the network despite having power. This is the most frequent cause for a single-node communication loss.
Damage to the CAN high or CAN low wires, or the power and ground circuits leading specifically to Sensor B, will interrupt communication. Corrosion at the connector or chafed wires near moving components are common culprits.
Loose pins, corrosion, or moisture intrusion within the sensor's electrical connector can prevent the establishment of a stable network link. This often occurs after recent service work or due to environmental exposure.
If a sensor was recently replaced with an incorrect part number or if the control module software is outdated, the network may fail to recognize the node. This can also happen if the vehicle battery was disconnected improperly during repairs.
While possible, an internal failure within the main computer preventing it from reading one specific sensor while others function is statistically rare. This should only be considered after all external wiring and the sensor itself have been ruled out.
No, in the vast majority of cases, this code is caused by a failed sensor or wiring issue, not the computer. Replacing the PCM is rarely the correct fix and should only be considered after exhaustive testing of the sensor and its circuit proves they are functional.
Driving is not recommended as the engine control system may not have accurate fuel pressure data, potentially causing poor performance, stalling, or inability to start. If the vehicle enters limp mode, it should be towed to a repair facility.
Multiple codes often indicate a problem with the network wiring itself, such as a short circuit or a bad ground, rather than multiple failed components. A single break in the CAN bus loop can prevent several modules from communicating simultaneously.
Clearing the code will turn off the light temporarily, but if the underlying communication fault (bad sensor or wire) remains, the code will return once the vehicle completes a drive cycle and the computer fails to receive data from the sensor again.