U1309

Code

DS U — Network/User

Fault: absence of communication with the automatic gearbox ECU: No signal / ECU absent

Brand: DS

Type: U — Network/User

Views: UK: 2 EN: 5 RU: 2

AI status

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Page language: EN

Causes

Blown fuse or relay supplying gearbox ECU
Loss of power or ground at gearbox ECU
Damaged or corroded connector at gearbox ECU
Open, shorted or high-resistance CAN bus wiring between gearbox ECU and gateway/BCM
CAN bus terminated incorrectly (missing or wrong termination)
Gateway/module configuration or programming issue (module not registered)

Symptoms

Transmission indicator or gearbox warning lamp illuminated
Instrument cluster message: gearbox not detected / check gearbox
Transmission may default to limp mode or not shift correctly
No transmission data (gear, range, torque converter lockup) visible on diagnostic tool
Related systems may flag communication faults (engine, ABS, traction)
Possible inability to engage drive/reverse or erratic behavior

What to check

Read all stored DTCs and freeze frame data; note time-stamps and ignition state
Scan network to view list of detected modules — confirm gearbox ECU is absent
Check battery voltage (key on) and ensure stable power supply (>12V)
Inspect and test gearbox ECU supply fuse(s) and related relays
Visually inspect gearbox ECU connector and wiring for corrosion, bent pins, water entry or damage
Check chassis ground(s) and ECU ground continuity to body/negative battery

Signal parameters

Typical CAN idle voltages at ECU connector (ignition ON): CAN_H ≈ 2.4–3.6 V, CAN_L ≈ 0.8–2.6 V; dominant (recessive) idle ≈ 2.5 V each
Dominant (bus active) voltages typically ~CAN_H 3.5 V and CAN_L 1.5 V (differential ~2.0 V)
Typical CAN data rates used on powertrain networks: commonly 500 kbps (some systems 250 or 125 kbps) — confirm for vehicle
Expected behavior: periodic gearbox status/heartbeat messages while ignition ON; absence = no transmit from ECU or bus open
Short to battery or ground will pull both lines away from expected voltages; open bus may show both lines stuck at supply or ground level

Diagnostic algorithm

Verify vehicle-specific documentation and wiring diagrams before starting. Note safety precautions for airbags and immobilizer.
Confirm the U1309 is current (not historic). Record freeze-frame and note when code set (key state, engine on/off).
Use a scan tool to enumerate modules on the vehicle CAN/gateway. Confirm gearbox ECU is not present and check for other network faults (U0100, U0073, U1000 etc.).
Check battery voltage and condition. Charge or connect a stable supply if voltage is low. Re-scan after stable voltage restored.
Inspect fuses/relays for gearbox ECU power circuits and replace if blown. Verify presence of ignition/switched 12V at ECU power pin with meter.
Disconnect battery per OEM procedure if required for connector inspection. Visually inspect gearbox ECU connector and harness for corrosion, bent pins, water, or rodent damage. Repair as required.
With ignition ON (engine off) measure CAN_H and CAN_L at gearbox ECU connector and at gateway/BCM CAN splice points. Compare voltages and watch for correct recessive/dominant behavior with an oscilloscope if available.
Perform continuity and short-to-ground/battery checks on CAN pair between gearbox ECU and gateway/BCM (with battery disconnected where required by procedure).
If wiring, connectors, fuses and grounds are good but no communication, check gateway/BCM configuration — confirm gearbox ECU ID and that it is expected on that bus. If module was replaced recently, check programming/parameterization steps.
If ECU receives power and bus is healthy at the harness but still does not communicate, consider ECU internal fault — consult manufacturer procedures for ECU replacement and required programming/security matching.
After repairs, clear codes, perform key cycles and road test to verify gearbox ECU appears and related faults do not return. Re-scan and monitor live data for stability.

Likely causes

Blown ECU supply fuse or faulty ignition feed
Corroded/loose ECU connector pins or water ingress in junctions
Broken or chafed CAN pair in harness near gearbox or harness junction
Ground lead corrosion or high-resistance ground at gearbox mounting point
Gateway/module reset or software mismatch after replacement or battery disconnect
Gearbox ECU failure (electronic fault)

Fault status

⚠️ Status

No communication received from automatic gearbox ECU. Possible causes: ECU absent/unpowered, connector/wiring fault, CAN bus issue, gateway/configuration or ECU internal failure.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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