What it means
Open circuit on input power line D of the control module (fourth supply rail). A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.
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 D is a fourth supply path to a control module. U3014 sets when the module detects that this line is open, which can interrupt module operation or communication and affect functions that rely on its data.
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 the reporting module and any related communication or supply faults.
- Check live data for the module's line D supply status and compare it with its other power inputs when possible.
- Inspect the line D fuse, fuse contacts, module connector, and harness for a blown fuse, corrosion, loose terminals, or damage.
- With the circuit isolated according to the manufacturer's procedure, test continuity on line D from its supply point to the module.
- If continuity is good, measure voltage drop under load and compare the line D supply at the module with the manufacturer's specification.
Common fixes
- Replace a blown line D fuse after finding and addressing the reason it opened.
- Clean and secure line D fuse or module connector contacts.
- Repair an open, damaged, or high-resistance section of the line D wire.
- Repair or replace the module if its line D input is correct at the connector but the fault persists.
Can I keep driving?
The lost fourth supply can make the module or dependent functions unavailable, so avoid driving if this affects powertrain control or a safety system. Stop if warning lights are accompanied by limp mode, shutdown, or abnormal vehicle behaviour.
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.