What Does U300E Mean?
DTC U300E indicates that a control module has detected a fault with the ignition switch input for the On (Run) position specifically. Unlike U300D which covers On/Start, this code isolates the Run-only signal. The Run position input tells modules that the engine should be operating and all run-dependent systems should be active. A fault here means the module is not reliably receiving the run-position signal from the ignition switch.
Common Causes
35%
Ignition switch Run contact worn or failed — the switch does not reliably provide signal when in the Run detent position
25%
Wiring fault in the Run-position signal circuit — open conductor, chafed wire, or poor splice between the switch and the module
20%
Corroded or loose connector terminal on the Run-position input at the BCM or affected module
20%
Ignition relay failure or ignition fuse contact degradation on the Run circuit power feed
Diagnostic Steps
1
Step 1: Monitor the scan tool for ignition switch Run position — with the key in the Run position, verify the signal is stable and does not flicker; gently wiggle the key in the cylinder while monitoring.
2
Step 2: Measure voltage at the module's Run input pin with the key in Run — should read a stable 12V or battery voltage; any instability or voltage below 10V indicates a circuit problem.
3
Step 3: Test the ignition switch in isolation — disconnect the switch connector and measure continuity on the Run-position contact; rotate the key through all positions to verify the Run contact closes only in the correct position.
4
Step 4: Check the ignition relay (if the Run circuit is relay-fed) — verify it clicks on when the key is turned to Run, and check output voltage at the relay under load.
5
Step 5: Trace the Run signal wire from the ignition switch through the harness to the module — check for any inline connectors, splices, or junction points that could be causing resistance or intermittent contact.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
DTC U300E indicates that a control module has detected a fault with the ignition switch input for the On (Run) position specifically. Unlike U300D which covers On/Start, this code isolates the Run-only signal. The Run position input tells modules that the engine should be operating and all run-depen...
The most common cause of U300E (Ignition Input On) is: Ignition switch Run contact worn or failed — the switch does not reliably provide signal when in the Run detent position
Typical repair costs for U300E range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Loss of the Run-position signal can cause the vehicle to stall or fail to recognize that the engine should be running, potentially disabling fuel injection, ignition, or other critical run-dependent systems. Do not drive if stalling is occurring.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U300E 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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