U0103

Code

HYUNDAI U — Network/User

Lost Communication With Gear Shift Module | Lost Communication With Gear Shift Control Module “A”

Brand: HYUNDAI

Type: U — Network/User

Views: UK: 15 EN: 37 RU: 30

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open, shorted, or high-resistance wiring on CAN bus between modules
Corroded, loose, or damaged connector at Gear Shift Control Module
Blown fuse or loss of module power/ground
Failed Gear Shift Control Module
Faulty ABS/TCM/ECM/BCM or other module on same CAN circuit interfering with bus
Intermittent connection due to water intrusion or damaged harness

Symptoms

Gear selector not responding or limited shift functionality
Transmission may default to limp/limited mode
MIL or transmission warning light illuminated
Inability to perform certain shift-by-wire functions (Park, Neutral detect)
Stored U0103 and possibly other U0xxx network codes
Intermittent or no communication with the shift module on a scan tool

What to check

Scan vehicle with a bidirectional scan tool and record all U0xxx and transmission related codes
Verify module presence on network (attempt to communicate with Gear Shift Control Module)
Check battery voltage and charging system; low voltage can cause network faults
Inspect fuses and relay(s) for the shift module circuit
Visually inspect connectors and wiring to the Gear Shift Control Module for corrosion, damage, or loose pins
Measure CAN bus voltages and continuity at the shift module connector

Signal parameters

CAN bus idle voltage: approx. CAN_H ~2.5 V and CAN_L ~2.5 V (each to chassis ground)
Dominant state on CAN: CAN_H ~3.5 V, CAN_L ~1.5 V (differential ~2.0 V)
Typical battery supply to module: ~12 V with key ON/crank
Module ground resistance: low ohms to chassis (
No short between CAN_H and CAN_L (should show high resistance except through transceivers)

Diagnostic algorithm

Read and record all DTCs and freeze frame data. Clear codes and attempt to reproduce; note persistence.
Verify vehicle battery condition and system voltage under load. Recharge or replace if low.
Check fuses and power/ground circuits for the Gear Shift Control Module. Back-probe module supply pin with key ON to confirm approx. battery voltage and good ground.
Inspect connector and wiring to the shift module for corrosion, bent pins, or damage. Repair any visible issues.
Attempt communication with the module using a factory scan tool. If no response, check for other modules on same CAN network to see if multiple modules are non-communicative.
Measure CAN_H and CAN_L at the shift module connector with key ON using a digital multimeter and then with an oscilloscope if available. Look for the idle voltages and proper differential waveform. Check for shorts to ground or battery.
If bus idle voltages are abnormal, disconnect the shift module and re-measure the bus. If the bus returns to normal with module disconnected, suspect the module is pulling the bus low (module fault).
Perform a wiggle test on the harness while monitoring communication to locate intermittent failures. Inspect routing where harness flexes or passes through body seams.
If wiring and bus are good, consult manufacturer procedures for reprogramming or initializing the Gear Shift Control Module. Reflash or update software if recommended.
If available, substitute a known-good shift module or have the module bench-tested by a qualified repair facility before replacement.
After repair, clear codes and verify normal operation and communication. Road test to confirm issue resolved.

Likely causes

Loose or corroded connector at the Gear Shift Control Module
Power or ground fault to the Gear Shift Control Module
Short between CAN_H and CAN_L or to battery/ground
Failure of the Gear Shift Control Module
Another module driving the bus incorrectly (stuck dominant)
Damaged CAN wiring at harness chafe points

Fault status

⚠️ Status

Lost communication between the vehicle network and the Gear Shift Control Module (Gear Shift Control Module “A”). Module not responding on CAN bus.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-4 hours

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U0103 — Lost Communication With Gear Shift Module | Lost Communication With Gear Shift Control Module “A”