What it means
Open circuit on input power line C of the control module (third supply rail, e.g. for redundant power on safety-critical modules).
At a glance
- Usually lights the warning light of the system that lost communication
- The engine or gearbox may go into limp mode
How it works
Input power line C is a third supply path to a control module, which may provide a separate or redundant feed. U3013 sets when that line is open and the module cannot detect the expected power through it; the module or dependent functions may become unavailable.
Common causes
Most likely first.
- Supply fuse blown
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules and save freeze-frame data to identify which module reports the open line C fault and what functions are affected.
- Check the live supply status for line C, if available, and compare it with the module's other power inputs.
- Inspect the line C fuse, fuse contacts, connectors, and harness for a blown fuse, corrosion, looseness, or damage.
- With the circuit safely isolated as specified by the manufacturer, test line C continuity from its fuse or supply point to the module.
- If continuity is present, check for voltage drop under load and verify the module connector pin and supply against the manufacturer's specification.
Common fixes
- Replace a blown line C fuse after checking for a short or overload.
- Clean and secure corroded or loose line C fuse and connector contacts.
- Repair an open or damaged wire in the line C supply circuit.
- Repair or replace the module only if line C power reaches its connector correctly but the fault remains.
Can I keep driving?
Because a third module supply is lost, dependent functions may shut down or enter limp mode; avoid driving if the affected module controls a safety or powertrain system. If the vehicle's behaviour changes or a critical warning appears, stop somewhere safe and arrange diagnosis.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.