U1117 — Fault: no communication with the intelligent hydraulic unit ECU: No signal

Causes

• Power or ground missing to the IHU ECU (blown fuse, disconnected connector, poor ground).
• Open, short or high resistance in CAN bus (or vehicle network) wiring to the IHU.
• Faulty or corroded connector at the IHU or along the bus.
• Missing or incorrect bus termination (open/removed or shorted termination resistor).
• Low vehicle battery voltage or intermittent supply.
• IHU ECU internal failure or stopped/crashed application software.

Symptoms

• U1117 stored in vehicle ECU memory; unable to communicate with IHU via a scan tool.
• Warning lamp or message related to hydraulic/ABS/ESP/leveling/suspension systems (depends on vehicle configuration).
• Related hydraulic functionality reduced, limited, or disabled (system enters limp or fail‑safe mode).
• Intermittent or permanent loss of the functions controlled by the IHU.
• Multiple network communication errors or other U‑codes present.

What to check

• Record all stored codes, freeze frame data and any additional U‑ or U0xxx codes before clearing.
• Verify battery voltage with ignition ON and engine OFF (>12.2 V recommended); check charging system.
• Visually inspect IHU connectors and wiring for corrosion, water ingress, bent pins, or physical damage.
• Check fuses and relays for the IHU power/ignition supply; verify presence of supply and ground at the ECU connector.
• Attempt to communicate with the IHU using a diagnostic tool; confirm module not present or not responding.
• Measure CAN bus idle voltages and resistance across CAN_H and CAN_L; check for proper termination (~60 Ω).

Signal parameters

• CAN bus idle (recessive): both CAN_H and CAN_L sit near vehicle reference midpoint (~2.5 V).
• CAN bus dominant state: CAN_H typically rises and CAN_L falls (examples: CAN_H ~3.5–4.0 V, CAN_L ~1.0–1.5 V).
• Differential signaling: expect usable dominant/recessive voltage swings on scope; absence indicates open/short.
• Termination: approximately 60 Ω measured between CAN_H and CAN_L with ignition ON (two 120 Ω resistors in parallel).
• Typical CAN data rates for body networks: common values 250 kbps or 500 kbps — confirm rate from factory documentation.
• No periodic messages from IHU on the bus (no TX frames from module) is consistent with a 'no signal' failure.

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