U300D code meaning
Ignition Input On/Start
What U300D means
U300D concerns the line that should be live in On and Start only, which GM calls Run/Crank Ignition 1; in GM's 2012 truck wiring manual it is active in run and crank and inactive in off and accessory. A module sets the code when this line and the power mode on the bus disagree. GM's PIT5817A for 2020–2021 Envision, CT4, CT5, Escalade, Corvette, Tahoe, Suburban and Yukon shows the typical case: the instrument cluster stores U300D while the ECM, TCM and brake module log P2535, often after remote start, and the customer finds a dead battery and a service engine lamp. The BCM's driver for the ignition main relay stays on after key-off and keeps circuit 5199 powered, so the line remains live with the car off; the fix is a new BCM. The cluster's code itself is the witness, not the cause.
U300D at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U300D
- Battery repeatedly discharged after the car was parked
- Service engine lamp at start-up with P2535 in other modules
- Cluster or other modules staying awake with the ignition off
Common causes of U300D
- Most likelyBody control module keeping the run/crank relay energized after key-off
- PossibleRun/crank relay sticking closed or failing to close
- PossibleBlown fuse or open wire in the run/crank feed to the module
- Less likelyBackfeed from an aftermarket device tapped into the run/crank circuit
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Ignition inputIgnition relayBody control moduleIgnition wiring
What each part of U300D means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 0D | The exact fault in that area. |
What to do next
- Note U300D and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U300D
What does U300D mean?
U300D means "Ignition Input On/Start". U300D concerns the line that should be live in On and Start only, which GM calls Run/Crank Ignition 1; in GM's 2012 truck wiring manual it is active in run and crank and inactive in off and accessory. It is a generic code, so it means the same on every make.
Is it safe to drive with U300D?
U300D does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U300D fail an emissions test?
U300D is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U300D to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U300D clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.