OBD-II code · Network (extended)
U300F Ignition Input Accessory
Fault on the ignition ACC (accessory) input. 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 U300F?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyIgnition switch contacts worn
- 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
- Ignition Input, Wiring
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.