U0100

• Several warning lights come on at once, or dashboard information disappears
• The function of the sending system (e.g. cruise control, instruments, sensor data) stops working
• Codes may appear and disappear when the battery is weak or during cranking

• Blown fuse, broken power supply or ground for the sending unit
• Chafed or broken CAN-High / CAN-Low wires or connector corrosion
• Weak battery or voltage drop during cranking
• Missing coding / software mismatch after a unit was replaced

1. Scan all modules: note which unit the code is read from and which unit it points to.
2. Measure battery voltage (≥12.4 V engine off, 13.8–14.7 V running); with a weak battery, communication codes can be false.
3. Check the fuse, power supply and ground of the unit that should be sending the message.
4. Measure CAN resistance at the OBD socket: with the ignition off, about 60 Ω is expected between CAN-H and CAN-L.
5. Clear the code and start the car; if it returns immediately, the unit or wiring is likely, if it comes and goes, a connector or poor contact is likely.

1. Repair a blown fuse, loose ground or corroded connector.
2. Repair a damaged CAN wire while keeping its twisted-pair structure.
3. If a unit was newly fitted, code it to the car / update its software.
4. If the unit itself is faulty, replace it and code it.

• Kia: Lost Communication With Engine Control Module/Powertrain Control Module

• U0101Lost Communication with TCM
• U0102Lost Communication with Transfer Case Control Module
• U0103Lost Communication With Gear Shift Module
• U0104Lost Communication With Cruise Control Module
• U0105Lost Communication With Fuel Injector Control Module
• U0106Lost Communication With Glow Plug Control Module

This page is general information; an exact diagnosis needs measurements and a technician’s check.