U0103: Lost Communication With Gear Shift Control Module A
What to do
The car will hold whichever gear it is in and may refuse to accept a new selection.
Take the parking situation seriously if this is a car with a small lever, dial or buttons rather than a traditional gearstick. On those, park is not a mechanical position you push the lever into — it is a request that an actuator carries out — so it may not engage when you expect it to. Use the parking brake every time you leave it, and check the dashboard actually shows P before you get out. On a slope, apply the parking brake before releasing the footbrake.
Get it recovered rather than driven far. As with all network codes, this rarely means the module itself has failed — its wiring, its connector and its power supply come first.
What this code means
The gear shift module has stopped being heard from. The general reasoning is at U0100.
On a shift-by-wire vehicle this module is the only thing that knows what the driver asked for, because there is no mechanical link between the selector and the gearbox — the point made at P0820, and its consequence arrives here in full. The lever, dial or buttons report to this module, and the module tells the transmission. Break that conversation and the request never reaches anything.
So the vehicle holds the gear it is in and will not accept a new selection, including park. That is worth stating plainly: park is an actuator carrying out a request, not a mechanical fact, so a vehicle that cannot be shifted out of drive also may not reliably go into park when the driver expects.
The parking brake is mechanically independent on most vehicles and is the thing to rely on, which is the same practical advice P0820 gives and the reason it is repeated here.
On vehicles with a conventional mechanical lever the consequences are milder — the gearbox still receives the lever's position through the transmission range sensor — and the complaint is usually a display showing the wrong gear or refusing to allow manual mode.
Likely causes
Start here
- Corroded or loose connector · easy
- Damaged data bus wiring · moderate
- Failed power or earth supply to the module · moderate
Less common
- Water ingress into connector · moderate
- Faulty gear shift module · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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