What it means
Wake-up signal B voltage above expected range. 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
How it works
Wake-up circuit B is the second path that signals a control module to become active. The module monitors its voltage and sets U3020 when circuit B rises above the expected range, consistent with a short to power. This abnormal signal can keep the module from waking or communicating correctly.
Common causes
Most likely first.
- Wiring shorted to battery
- 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
- Save freeze-frame data and scan all modules for communication faults to see which module is affected and when circuit B went high.
- Compare circuit B status or voltage in live data, if available, with the ignition state and expected wake sequence.
- Inspect the second wake-up path and its connectors for damage or contact with a battery or ignition power wire.
- With the circuit isolated as directed by the manufacturer, test for a short from wake-up circuit B to a power feed.
- If circuit B wiring passes, check gateway routing and CAN network termination against the manufacturer's specification.
Common fixes
- Repair circuit B wiring that is shorted to battery or another power feed.
- Repair connector damage or bridging terminals on the second wake-up path.
- Correct gateway routing or configuration if it is causing the abnormal signal.
- Repair the CAN network or replace a terminating resistor only after confirming it is out of specification.
Can I keep driving?
The module may fail to wake or communicate, disabling functions that depend on it. Limit driving if those functions are needed for safe control, and stop if a safety-related system is affected.
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.