U0285

Code

Generic U — Network/User

Lost Communication With Active Grille Air Shutter Module B

Brand: Generic

Type: U — Network/User

Views: UK: 33 EN: 100 RU: 64

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Page language: EN

Causes

Open or shorted wiring on the module communication bus (CAN/LIN)
Faulty connector or poor terminal contact at the Active Grille Air Shutter Module B
Module power or ground supply failure
Module hardware/software fault (module internal failure)
Bus termination or wiring short to battery/ground causing network error
Intermittent connection due to corrosion, moisture, or damaged harness

Symptoms

Malfunction indicator lamp or message related to grille shutter or emissions airflow control
Active grille shutter(s) stuck open or closed, reduced grille shutter operation or incorrect shutter position
Reduced engine or cooling system efficiency in some vehicles (possible increased fan activity)
Related HVAC or aero-control system warnings on cluster
Other modules reporting communication errors or multiple U0xxx communication codes

What to check

Read all stored DTCs and freeze frame data with a capable scan tool; note ignition state and timestamps
Verify whether the Active Grille Air Shutter Module B appears in the scan tool’s module list and if it responds to requests
Scan for other U0xxx codes — determine if a wider bus problem exists
Visually inspect the module connector and nearby harness for damage, corrosion, push/pull retention, or signs of water intrusion
Check relevant fuses and relays for the module’s power feed
Check battery voltage and bulk ground condition (engine off and key on)

Signal parameters

Presence of periodic CAN frames from the Active Grille Air Shutter Module B (module-specific PGNs/IDs — should be present when module awake)
CAN bus idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (or 2.5 ± 0.5 V) with key on and module present
Differential CAN voltage during activity ≈ 1.0–3.0 V depending on TX state
Supply voltage at module Vbatt with ignition on (expected near battery voltage)
Ground continuity from module chassis/ground pin to vehicle ground (low ohms)
Bus termination resistance ~60 ohms across CAN_H and CAN_L (two 120 ohm in parallel)

Diagnostic algorithm

Use a scan tool to read U0285 and any related codes; record conditions (key on, engine running).
Confirm whether the grille shutter module B is present in the tool’s ECU list and attempt to communicate; note if it is completely non-responsive or intermittently responding.
Inspect the module and connector for corrosion, bent pins, water damage, or poor latch. Repair or reseat connector if needed and re-scan.
Verify fuses and measure supply voltage at the module power pin with ignition ON. Repair wiring or replace fuse if no battery voltage present.
Check ground: measure resistance between module ground pin and vehicle chassis ground (should be low,
Backprobe CAN_H and CAN_L at the module connector. With ignition ON, check idle voltages and observe differential signal with a scope or lab tool while polling the module. Look for bus-off, stuck dominant, or no activity.
If the bus shows no activity or abnormal voltages, inspect wiring harness between module and nearest junction/connector for opens or shorts; perform wiggle test to reproduce intermittent faults.
Check termination resistors and isolation of the CAN pair; disconnect the module and measure termination across the CAN bus to confirm ~60 ohms total.
If wiring and power/ground are good but no communication, attempt to communicate with the module while supplying a known-good supply (bench test) only if procedures and safety allow, or consult OEM module bench/test procedures.
Repair wiring, connector, or replace the module only after confirming failure. Clear codes and perform functional test and road or activation test to confirm repair.
If multiple modules show comms loss, investigate main gateway or bus power/termination and perform full network diagnostics.

Likely causes

Loose or corroded connector at the active grille shutter module B
Blown fuse or loss of module supply voltage/ground
Broken or chafed CAN high or CAN low conductor between the module and the rest of the network
CAN bus shorted to battery or ground causing node suppression or bus-off condition
Module failed after water intrusion or mechanical damage