What does this code mean?
The wording below belongs to the named make and communication. Match the complete code, reporting module, model year and engine before applying it.
A code identifies a detected condition, not a part that must automatically be replaced.
Manufacturer communications
7Original wording in English
CADILLAC, CHEVROLET, GMC
Reported code forms U0121
This Preliminary Information communication provides information to the technician about vehicle with Service ABS and/or Traction control lights/message on, Service Power Steering System, Service Suspension System, and…
CADILLAC, CHEVROLET, GMC
Reported code forms U0121
This Preliminary Information communication provides information to the technician for a reduced power message, steering assist, engine stall or the instrument panel, radio, and or Heater-Vent-Air Conditioning go blank…
CADILLAC, CHEVROLET, GMC
Reported code forms U0121
This Preliminary Information communication provides information to the technician about vehicle with Service ABS and/or Traction control lights/message on, Service Power Steering System, Service Suspension System, and…
CADILLAC, CHEVROLET, GMC, HUMMER
Reported code forms U0121
This technical bulletin provides repair information to correct customer concerns of loss of high speed GMLAN communications, intermittent no crank, IP gauge fluctuation, intermittent door lock cycling /chime operation,…
CADILLAC, CHEVROLET, GMC
Reported code forms U0121
This Preliminary Information communication provides information to the technician for a reduced power message, steering assist, engine stall or the instrument panel, radio, and or Heater-Vent-Air Conditioning go blank…
CADILLAC, CHEVROLET, GMC
Reported code forms U0121
GMC: UNABLE TO COMMUNICATE WITH THE EBCM DTC U0121. *NJ VEHICLES EQUIPPED WITH JL4. UPDATED 9/30/08. *PE UPDATED 6/27/11. *PE UPDATED 4/6/12. *PE
Check vehicle applicability
13A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.
| Make | Model | Model year |
|---|---|---|
| GMC | SIERRA 2500 | 2019 |
| GMC | SIERRA 2500 | 2018 |
| GMC | SIERRA 2500 | 2017 |
| GMC | SIERRA 2500 | 2016 |
| GMC | SIERRA 2500 | 2015 |
| GMC | SIERRA 2500 | 2014 |
| GMC | SIERRA 2500 | 2013 |
| GMC | SIERRA 2500 | 2012 |
| GMC | SIERRA 2500 | 2011 |
| GMC | SIERRA 2500 | 2010 |
| GMC | SIERRA 2500 | 2009 |
| GMC | SIERRA 2500 | 2008 |
Historical records · 243 · Historical vehicle association; OBD-II compatibility is not established by this record.
Before replacing a part
Record codes and freeze-frame data. Check battery condition, related codes and visible wiring or hose damage. Follow the vehicle's diagnostic procedure and test results before replacing parts.
Can I keep driving?
A code alone cannot establish whether driving is safe. A flashing malfunction light, severe shaking, overheating, oil-pressure warning or loss of braking or steering needs prompt attention. Stop in a safe place and seek assistance when control or engine safety is affected. Follow the vehicle handbook.