U0046 indicates a communication fault on the vehicle's Controller Area Network (CAN) Bus C, which is the high-speed data network that allows the engine/powertrain control module and other modules to exchange information. The code sets when a module detects that Bus C is open, shorted, or otherwise unable to pass messages reliably. It is a network code, not a sensor or emissions-component failure.
Open, short-to-power, short-to-ground, pinched, corroded, or poorly seated harness connectors on the high-speed CAN C network are the most common cause. This includes damage at splices, pass-through connectors, and module pins.
High-speed CAN buses require two 120-ohm termination resistors, one at each end, giving a measured resistance near 60 ohms across the bus. A missing, open, or shorted resistor can prevent message exchange and set U0046.
A control module connected to Bus C can fail internally and disrupt the entire network by shorting the CAN high or low lines or transmitting invalid messages. Identifying the offending module often requires selective isolation.
Low battery voltage, weak alternator output, poor module ground points, or blown fuses can cause modules to drop off the bus and store communication codes even when the wiring is intact.
Although U0046 may point to the PCM as the module reporting the fault, an actual PCM failure causing this code is uncommon and should only be considered after wiring, termination, power/ground, and other modules have been ruled out.
It can be. Because Bus C is the high-speed network used by powertrain modules, a fault can cause warning lights, loss of module communication, and in some cases drivability or starting problems. It should be diagnosed rather than cleared and ignored.
If the vehicle starts and runs normally, short trips may be possible, but communication faults can worsen or cause unexpected warning-lamp behavior. Diagnosis is recommended as soon as practical.
Usually no. U0046 is most often caused by wiring, connector, termination-resistor, power/ground, or another module issues. PCM failure is genuinely uncommon for this code, so the PCM should be the last component suspected, not the first.
When a CAN bus stops communicating, multiple modules lose contact with each other and each one stores its own communication-fault code. The root cause is typically a single wiring or module fault on the shared bus, not several independent failures.