U0284: Lost Communication With Active Grille Shutter Module A (Meaning, Causes, Fixes)

What U0284 means

Many newer cars and trucks have an active grille shutter (GM calls it the Aero shutter): a set of motor-driven louvers behind the grille that the engine computer opens and closes. The shutter's actuator talks to the engine computer over a communication line. Subaru's service procedure describes it as a LIN communication link, and Mitsubishi calls it the engine communication signal. Mitsubishi's service information says U0284 sets with the ignition on when the ECM cannot receive the communication signal from the active grille shutter, and lists two possible causes: the harness and connectors (communication line open or shorted) and the active grille shutter itself. Vehicles with two shutters can also set U0285 for the second (lower) shutter, as GM's bulletin 21-NA-077 shows. GM also notes that on its trucks and SUVs a shutter performance problem will always set P059F together with U0284 for the upper shutter (P05AE and U0285 for the lower one), so don't be surprised to see them together. The sources differ on how to repair wiring damage: Subaru bulletin 07-140-18 (2017-2019 Impreza) says not to repair the wiring or clean the terminals, and to replace both the bulkhead wiring harness and the shutter assembly if corrosion or an open circuit is found. GM's bulletin 21-NA-077 says to repair the engine wiring harness if it is corroded or damaged, but to replace the shutter (not the wiring) if corrosion is found in the shutter's jumper harness. Follow the procedure for your make. The bulletins cited are for specific models (listed in the sources), so check whether one applies to your vehicle.

Severity: can I keep driving?

Drive with caution, fix soon

Get it diagnosed soon. None of the sources below gives U0284 a severity rating or says the car is unsafe to drive. GM says drivers usually notice a check engine light, and Mitsubishi's service information lists no fail-safe mode for this code. It is an electrical communication fault with the grille shutters, so until it is fixed, keep an eye on the temperature gauge and stop driving and get help if the engine starts to overheat or other warning lights come on.

Common symptoms

• Check engine light on (GM bulletin 21-NA-077, GM TechLink)
• Other communication or shutter codes set at the same time, such as U0285, U1345 or P059F (GM TechLink, GM bulletin 21-NA-077)
• Often no other noticeable symptom; Mitsubishi's service information lists no fail-safe mode for U0284

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

1. An open or shorted communication wire between the engine computer and the shutter (Mitsubishi service information)
2. Water getting into the shutter harness or connector and corroding the wires or terminals; Subaru bulletin 07-140-18 describes this at connector B63 on 2017-2019 Imprezas
3. Shutter wiring pinched at the radiator support (GM TechLink, citing GM bulletin 22-NA-252)
4. The in-line connector between the engine harness and the shutter not fully connected, not held by its clip, or grounded on the radiator (GM TechLink)
5. A loose fuse for the shutter, or a soft (poorly seated) connection at the shutter actuators (GM bulletin 21-NA-077)
6. High resistance in the engine harness or the shutter jumper harness (GM bulletin 21-NA-077)
7. A failed active grille shutter assembly or actuator (Mitsubishi service information, Subaru and GM bulletins)

Diagnostic steps you can do

1. Read all codes first. Mitsubishi's procedure says if U0284 shows up with another U-code, diagnose that other code first.
2. Check that the battery voltage is at least 10 volts with the ignition on before testing (Mitsubishi service information).
3. Check the fuse for the shutter and make sure it is not loose (GM bulletin 21-NA-077).
4. Find the shutter connector behind the grille, disconnect it and look for corrosion, green crust or water on both sides; Subaru says to do this before any other electrical testing.
5. Follow the shutter wiring and look for pinched, chafed or broken wires, especially where it passes the radiator support (GM TechLink).
6. Make sure the in-line and shutter connectors are fully seated and held by their clips (GM TechLink, GM bulletin 21-NA-077).
7. Check for technical service bulletins for your vehicle that mention U0284.

Typical fixes

• Reseat a loose connector or fuse (GM TechLink, GM bulletin 21-NA-077)
• Repair pinched or damaged wiring in the engine harness, as GM's bulletins direct
• On models covered by Subaru bulletin 07-140-18, replace the bulkhead wiring harness and the shutter assembly if corrosion or an open circuit is found, rather than repairing the wires
• Replace the shutter assembly when its own jumper harness is corroded (GM bulletin 21-NA-077) or when wiring and power checks pass and it still does not communicate (Mitsubishi service information)
• If connectors show water but no corrosion and the seals are intact, GM's bulletin says to apply dielectric grease to the connector

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

Related codes

• U0155 Lost Communication With Instrument Panel Cluster (IPC) Control Module
• U0140 Lost Communication With Body Control Module (BCM)
• U0121 Lost Communication With ABS Control Module
• U0109 Lost Communication With Fuel Pump Control Module (FPCM)
• U0401 Invalid Data Received From ECM/PCM A

Also listed in this guide:

All Network communication codes (U0xxx) →

FAQs

Sources

1. Mitsubishi service information: DTC U0284 Lost communication with active grille air shutter module A (detection logic and possible causes)
2. Subaru of America service bulletin 07-140-18: DTC U0284, Additional Diagnostics Added (2017-19 Impreza), via NHTSA
3. GM service bulletin 21-NA-077: Information on Aero Shutter Related Diagnostic Codes (2019-2021 Silverado, Sierra, Tahoe, Suburban, Yukon, Escalade), via NHTSA
4. GM TechLink, mid-December 2022: Communication DTCs Set (U0284 and U0285, citing bulletin 22-NA-252)