OBD-II code · Network (extended)
U301B Control Module Wake-up Circuit A Low
Wake-up signal A voltage below expected range — short to ground. 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.
Is it safe to drive with U301B?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyWiring shorted to ground
- Less likelyGateway module routing CAN messages incorrectly
- Less likelyCAN 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
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.5–2 h
- Emissions test
- Usually unaffected
- Parts involved
- Wakeup Circuit A, Wakeup Wiring
Related codes
- U301FControl Module Wake-up Circuit B Low
- U3018Control Module Input Power Circuit A/B Correlation
- U3019Control Module Input Power Circuit B/C Correlation
- U301AControl Module Wake-up Circuit A/Open
- U301CControl Module Wake-up Circuit A High
- U301DControl Module Wake-up Circuit A Performance
- U301EControl Module Wake-up Circuit B/Open
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.