U0033 indicates that the vehicle’s high‑speed communication bus (commonly a Controller Area Network) has been detected in an open condition. This means one or more modules cannot send or receive data, usually because a wire, connector, or bus component is broken. The malfunction triggers the MIL and can affect multiple vehicle systems.
The CAN bus wires may be broken, cut, chafed, or the connector pins may be bent, corroded, or loose, creating an open circuit that prevents communication.
A defective ECU or control module that drives the bus can fail internally, leaving the bus without a transmitter and causing an open condition.
Proper bus termination is required; resistors that are open, shorted, or out of specification can make the bus appear open.
A module lacking proper voltage may stop communicating, which can manifest as an open bus condition.
An improperly installed device that taps into the bus can disrupt communication or create an open.
In very rare cases the engine computer itself may malfunction, but this is seldom the root cause of an open bus.
No, the PCM is rarely the cause. Most often the problem lies in wiring, connectors, or a failed module on the bus.
You may be able to drive, but loss of communication with critical modules can cause reduced performance, stalling, and safety‑system warnings.
Battery replacement itself does not cause the code, but disturbing wiring during the job could expose an existing open circuit.
Measuring the resistance across the CAN high and CAN low lines at the DLC should be about 60 Ω; a reading far from this indicates a termination problem.