OBD2 Code U300F: ACC Circuit Input Fault
The U300F code indicates a problem with the accessory (ACC) position signal from the ignition switch to the control module. This circuit tells the module when the key is in the ACC position, powering accessories like the radio and windows without the engine running. The fault means the module sees an inconsistent, out-of-range, or missing signal on this circuit, which can disrupt systems that rely on knowing the ignition state. Per SAE J2012, U3000-U3FFF codes cover data network communication and input signal issues. The module compares the ACC logic state with other parameters to verify consistency, and a detected fault may trigger fail-safe modes in modules needing ignition position info.
1. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.
2. Most Common Causes
- Faulty or worn ignition switch in the ACC position
- Damaged, corroded, or high-resistance wiring in the ACC circuit
- Loose or corroded ignition switch connector
- Blown or poor-contact ACC circuit fuse
- Control module with internal signal detection failure
- Aftermarket electrical modification altering the ACC circuit signal
- Weak battery or charging system with voltage below specification
3. Symptoms You Will Notice
- Accessories (radio, windows) not working or intermittent
- Engine may not start or start in wrong key position
- Warning lights on dash related to ignition or communication
4. Step-by-Step Diagnosis
Check for blown ACC fuse and replace if needed
Inspect ignition switch connector for corrosion or looseness
Test ACC circuit wiring for continuity, shorts, or high resistance
Verify battery voltage and charging system output
If wiring and switch are good, suspect control module fault
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, but accessories may not work and the engine may not start properly. It's best to diagnose and fix soon to avoid being stranded.
How much does it cost to fix?▼
Typically $100-$400, depending on whether it's a fuse ($10-$20), wiring repair ($100-$200), ignition switch ($150-$300), or control module ($300-$800).