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Home / DTC / U1124 — Fault: absence of communication with the pneumatic suspension ECU: No signal

U1124 — Fault: absence of communication with the pneumatic suspension ECU: No signal

Detailed page for trouble code U1124.

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Code

U1124

PEUGEOT U — Network/User

Fault: absence of communication with the pneumatic suspension ECU: No signal

Brand: PEUGEOT
Type: U — Network/User
Views: UK: 2 EN: 7 RU: 8
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Page language: EN

Causes

  • Loss of CAN/LIN communication with the pneumatic suspension ECU
  • Faulty pneumatic suspension ECU (power or internal failure)
  • Blown fuse or interrupted power/ground to the suspension ECU
  • Broken, shorted or corroded wiring/connectors between ECU and network
  • Network bus fault (open, short to battery/ground, missing termination)
  • ECU in sleep mode or not woken by wake-up signal/software issue

Symptoms

  • Suspension warning lamp or message on dash (e.g., 'suspension fault')
  • Incorrect ride height, vehicle sagging or inability to adjust level
  • Automatic height control disabled or stuck in limp/lowest mode
  • Unresponsive suspension controls via menu or switches
  • Other modules reporting related network errors or loss of function

What to check

  • Read and record all stored DTCs from all modules (full network scan)
  • Check battery voltage (key on and cranking) and condition
  • Inspect fuses and relays supplying the suspension ECU
  • Visual inspection of ECU connector(s) for corrosion, bent pins, water ingress
  • Measure power and ground at the pneumatic suspension ECU connector
  • Measure CAN_H and CAN_L voltages at the ECU with ignition ON

Signal parameters

  • CAN idle (recessive) voltages: approximately 2.4–2.6 V on CAN_H and CAN_L (both near mid-rail)
  • CAN dominant state: CAN_H rises (~3.5V) and CAN_L falls (~1.5V); dominant differential typically ~2V–3V
  • Expected bus termination: ~60 ohms total (two 120-ohm terminators in parallel)
  • Typical CAN bit rates used on vehicles: common values 125 kbps, 250 kbps or 500 kbps (confirm from wiring diagram)
  • Message frequency: suspension module messages typically periodic (tens to hundreds of ms) — verify with oscilloscope/scan tool
  • No responses or missing arbitration IDs for the suspension ECU indicates absent transmission

Diagnostic algorithm

  1. Verify the fault: clear codes, cycle ignition, re-scan to confirm U1124 reappears.
  2. Check vehicle battery voltage (≥12.4 V static) and charging system. Low voltage can cause modules to shut down.
  3. Inspect fuses/relays for the pneumatic suspension ECU circuit; replace if blown and re-test.
  4. Visually inspect and reseat the suspension ECU connector(s). Look for bent pins, corrosion, water ingress or damage.
  5. With ignition ON, measure power supply and ground at the ECU harness. If supply or ground missing, trace and repair wiring to source.
  6. Measure CAN_H and CAN_L at the ECU with a multimeter (recessive ~2.5 V). If voltages out of range, isolate wiring for short to battery/ground or open circuit.
  7. Measure termination resistance across CAN_H and CAN_L with battery disconnected or ignition OFF; expect ~60 Ω. If open or much lower, investigate wiring/connectors/terminators.
  8. Use a scan tool to request data from the suspension ECU. If no response, use an oscilloscope or CAN bus diagnostic tool to look for activity and differential signals.
  9. If another module is available, check whether it can see the suspension ECU ID on the bus. Check for bus-off frames or error counters.
  10. Repair wiring faults, corroded connectors, or replace faulty terminators. After repairs, clear codes and verify restoration of communication.
  11. If wiring and power/ground are good but no communication, suspect a failed pneumatic suspension ECU. Confirm by substitution with known-good unit or bench test per manufacturer procedures.
  12. After repair, perform function tests (ride height adjustment, recalibration/adaptation procedures) and confirm no further communication faults.

Likely causes

  • Disconnected or corroded connector at the pneumatic suspension ECU
  • Blown fuse or loss of power/ground to the suspension ECU
  • CAN bus short (CAN_H to battery or CAN_L to ground) or open circuit
  • Faulty pneumatic suspension ECU
  • Module in bus-off due to repeated errors (requires diagnosis with scope/scan tool)

Fault status

⚠️ Status
No communication with pneumatic suspension ECU: No signal
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

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