What Does U300C Mean?
DTC U300C indicates that a control module has detected a fault with the ignition switch input for the Off/On/Start positions. The module monitors the transition from Off to On (Run) and On to Start, and this code sets when the signal for these positions is out of specification. This could mean the switch is not cleanly transitioning between Off, On, and Start, or the signal levels are incorrect for those positions.
Common Causes
35%
Worn ignition switch internal contacts causing signal overlap or dropout between the Off, On, and Start detent positions
25%
Faulty ignition switch wiring — open or shorted conductor in the Off/On/Start signal wire
20%
Ignition lock cylinder mechanical wear causing the switch not to fully engage the correct detent position
20%
BCM input circuit failure or connector issue on the Off/On/Start signal pin
Diagnostic Steps
1
Step 1: Monitor ignition switch position on the scan tool — turn the key from Off to On to Start and back, verifying each position registers correctly without showing an incorrect state during transitions.
2
Step 2: Check the ignition lock cylinder for mechanical wear — verify the key rotates smoothly through all detents and that the switch fully engages each position; a sloppy or binding cylinder can prevent proper switch contact.
3
Step 3: Backprobe the Off/On/Start signal wire at the BCM connector — measure voltage in each key position and compare to wiring diagram specifications; look for incorrect or floating voltage levels.
4
Step 4: Disconnect the ignition switch connector and test the switch in isolation — measure continuity through the switch contacts in each detent position per manufacturer specifications.
5
Step 5: If the switch and wiring test good, verify the BCM connector pin for the Off/On/Start input is not corroded or loose — clean and reseat the connector; if the code persists, the BCM may need replacement.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
DTC U300C indicates that a control module has detected a fault with the ignition switch input for the Off/On/Start positions. The module monitors the transition from Off to On (Run) and On to Start, and this code sets when the signal for these positions is out of specification. This could mean the s...
The most common cause of U300C (Ignition Input Off/On/Start) is: Worn ignition switch internal contacts causing signal overlap or dropout between the Off, On, and Start detent positions
Typical repair costs for U300C range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A faulty Off/On/Start signal can cause the vehicle to not properly recognize key-on or key-start commands, potentially resulting in no-start conditions or failure to cut off fuel/ignition when the key is turned off. Diagnose promptly for safe operation.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U300C to identify the root cause.
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Quick Info
Category
Network
System
Ignition Switch / Power Distribution System
Difficulty
Type
Generic (SAE)
Recommended Tools
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