U0115

Code

HYUNDAI U — Network/User

Lost Communication With ECM/PCM “B”

Brand: HYUNDAI

Type: U — Network/User

Views: UK: 38 EN: 36 RU: 21

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Page language: EN

Causes

Open, shorted or intermittent CAN/LIN wiring between ECM/PCM B and network
Faulty ECM/PCM B (power, ground, internal failure)
Poor or corroded connector or pin at ECM/PCM B or network junctions
Failed termination resistor or improper bus termination
Other module on same network creating bus fault (short to battery/ground)
Blown fuse or loss of module supply/ignition power

Symptoms

MIL/DTC illuminated for communication fault
No engine/vehicle data from ECM/PCM B on a scan tool (missing PID groups)
Multiple modules show related U-codes or loss of data from ECM/PCM B
Possible no-start, limp-in mode, or reduced drivability if critical signals absent
Certain vehicle functions tied to ECM/PCM B may be inoperative (cruise, emissions systems, gauge/cluster data)
Intermittent faults or modules appear/disappear with ignition cycles or vibration

What to check

Read all stored U- and P-codes from every module; note freeze frame and occurrence count
Attempt to communicate with ECM/PCM B using a capable scan tool; verify which messages/PIDs are missing
Visually inspect ECM/PCM B connectors and nearby junctions for corrosion, bent pins, water intrusion, or damage
Check fuses and relays that supply ECM/PCM B power and ignition circuits
Check for TSBs, software updates, or module reprogramming notes from Hyundai
Check for recent repairs or aftermarket installations that may have disturbed wiring harnesses

Signal parameters

CAN bus (typical values): Recessive state — CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both lines near midrail)
Dominant state — CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ~2.0 V)
Measured idle differential voltage (CAN_H minus CAN_L) should be near 0 V with both ≈2.5 V; differential when active typically 1.5–2.5 V
Expected bus termination resistance with two 120 Ω terminators in parallel ≈60 Ω (measure between CAN_H and CAN_L with key off)
ECM/PCM B should transmit periodic heartbeat/engine messages — absence of those messages is the condition triggering U0115

Diagnostic algorithm

Verify the customer concern and retrieve all codes from all modules. Record freeze frame and occurrence counts.
Attempt communication with ECM/PCM B using a master-level scan tool. Note whether module responds to diagnostics or is completely non-responsive.
Visually inspect ECM/PCM B connectors, harness runs, and splice/junctions for damage, corrosion, moisture, or pin push-out. Repair any physical issues.
Check ECM/PCM B battery power and ground circuits: measure key-on battery presence at the module, and verify a good ground (low resistance to chassis). Repair any supply faults.
With ignition ON (engine off), measure CAN_H and CAN_L voltages at the ECM/PCM B connector. Compare to typical values (recessive ≈2.5 V). If voltages abnormal, trace for short to Vbatt or ground.
Measure resistance between CAN_H and CAN_L with key off — expected ≈60 Ω (verify terminators). If open/high, locate open terminator or disconnected module.
Use a scan tool or oscilloscope to monitor CAN traffic at several network nodes. Identify if ECM/PCM B messages ever appear or if bus noise/voltage spikes occur. Perform wiggle test on wiring to reproduce intermittent faults.
Isolate segments: disconnect suspected modules or branches (with precautions) to see if bus communication restores. Repair any shorted branches or replace damaged connectors.
If wiring and power/ground are confirmed good and the module still does not communicate, consult Hyundai service data for reprogramming/initialization procedures. Consider replacement of ECM/PCM B only after confirming module wiring and bus are good.
Clear codes and test drive to confirm whether U0115 returns. If intermittent, monitor for patterns (temperature, vibration, doors, accessory use).

Likely causes

Disconnected or corroded ECM/PCM B connector
Damaged CAN_H or CAN_L wiring from ECM/PCM B to junctions or gateway
Failed ECM/PCM B supply or ground circuit
Failed network termination (open 120Ω resistors or connector issue)
Short to battery or ground on one of the bus lines caused by chafed harness

Fault status

⚠️ Status

DTC U0115 set when the vehicle network diagnostic detects ECM/PCM 'B' is not responding or its expected messages are not present on the communication bus. The code indicates a communication fault (missing heartbeat or timed-out responses) and may be stored as active or intermittent depending on conditions.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 4.0 hours

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U0115 — Lost Communication With ECM/PCM “B”