U0103
Lost Communication With Gear Shift Control Module A
Communication / transmission
Generic OBD-II
High
What it means
U0103 sets when a module (usually the ECM/PCM or TCM) stops receiving messages from the gear shift control module, which manages gear selection — critical on shift-by-wire transmissions. The transmission may drop into a failsafe mode, refuse to shift, or misread the selected gear, so the car often becomes hard to drive normally until it's repaired.
High
Can I keep driving? Limited — losing the shift control module can force the transmission into a failsafe (limp) mode or prevent gear selection; drive gently and get it fixed soon.
Common symptoms
What you'll notice
- Transmission stuck in one gear or in limp/failsafe mode
- Gear selector reads wrong or won't select a gear (shift-by-wire)
- Check-engine and/or transmission warning light on
- Harsh, delayed, or no shifting
- No-crank or no-start on some shift-by-wire systems if Park/Neutral can't be confirmed
Common causes
Most likely first
- Damaged wiring or connector at the gear shift control moduleLikely
- Loss of power or ground to the shift moduleCommon
- CAN bus wiring fault between the shift module and the ECM/TCMCommon
- Failed gear shift control moduleLess often
- Corrosion or water intrusion at the shifter/module connectorLess often
How to diagnose & fix
Work through it in order
- Scan all modules and check whether the shift module responds at all.
- Inspect the shift module's connector, power, and ground for damage or corrosion.
- Check the CAN bus wiring between the shift module and the ECM/TCM for opens or shorts.
- Verify the module has proper power and ground with a meter.
- If wiring and power are good, the gear shift control module likely needs replacement and programming. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with U0103?+
Not really — a transmission that drops into limp mode or can't confirm gear position is unpredictable. Drive only as far as needed to get it repaired.
Can I just clear U0103?+
It'll clear but returns immediately if the module is still offline. This one needs the wiring or module fixed.
Related codes
Often seen with U0103
Read & clear U0103 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX