U0304 code meaning
Software Incompatibility With Gear Shift Control Module
What U0304 means
U0304 is stored when a control unit, usually the transmission controller, finds that the software or calibration identity of the gear shift control module does not match what it expects. GM's generic U03xx procedure (Saab 9-5, 2011) treats such codes as configuration faults: checked at 9-16 V with normal bus traffic, no circuit test, cured by setup or programming. Allison uses U0304 for its 6th-generation controls as Gear Shift Module 1 Incompatible: a 6th-generation push-button selector does not work with a 5th-generation TCM, and the selector must match the TCM calibration; U0333 covers selector 2. U0103 means lost contact, U0404 invalid data from the same module. The driver may be unable to select a range.
U0304 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0304
- Gear ranges cannot be selected or the selector does not respond
- Transmission warning or code shown on the selector display
- Code appears right after a selector or TCM was replaced
Common causes of U0304
- Most likelyShift selector generation or type does not match the TCM calibration (e.g. after replacement)
- PossibleShift module or TCM replaced or flashed without setup
- Less likelySoftware update aborted, wrong file loaded
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Gear shift moduleTransmission control moduleControl module software
What each part of U0304 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 04 | The exact fault in that area. |
What to do next
- Note U0304 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 U0304
What does U0304 mean?
U0304 means "Software Incompatibility With Gear Shift Control Module". U0304 is stored when a control unit, usually the transmission controller, finds that the software or calibration identity of the gear shift control module does not match what it expects. It is a generic code, so it means the same on every make.
Is it safe to drive with U0304?
Drive gently and only to a workshop. With U0304 the car can go into limp mode (reduced power) to protect itself.
Will U0304 fail an emissions test?
U0304 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 U0304 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 2 hours of work. This is a job for a workshop.
Will U0304 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.