U025F

Code

Generic U — Network/User

Lost Communication With Electronic Brake Booster Control Module B

Brand: Generic

Type: U — Network/User

Views: UK: 22 EN: 66 RU: 28

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Page language: EN

Causes

Faulty or disconnected connector at Electronic Brake Booster Control Module B
Damaged wiring or short/open on CAN High/CAN Low between the module and the network
Blown fuse or switched power feed to the brake booster control module
Poor or intermittent ground at the module
Failed Electronic Brake Booster Control Module B
CAN bus bus termination problem (open or wrong resistance)

Symptoms

Communication-related warning lights illuminated (ABS, BRAKE, ESC/VDC, or general warning lamp)
Brake assist not functioning as expected or reduced pedal assist (depending on vehicle design)
Loss of certain electronic brake features (auto-hold, regen braking coordination, hill assist)
Possible diagnostic trouble codes relating to other modules that rely on brake booster data
Erratic or no data from brake booster in scan tool

What to check

Connect a capable scan tool and confirm U025F and any related codes; note if module appears in network scan
Attempt to communicate with Electronic Brake Booster Control Module B (identify presence and live data)
Check for additional U-codes or B/C/P codes that indicate shared bus issues
Inspect fuses and relays that supply the brake booster control module
Visually inspect module connector and wiring for corrosion, bent pins, damage or water intrusion
Back-probe module power and ground pins with key ON; verify battery voltage and ground continuity

Signal parameters

CAN bus idle voltages (typical): CAN High ≈ 2.5 V, CAN Low ≈ 2.5 V (recessive state); dominant state: CANH ~3.5 V, CANL ~1.5 V
Termination resistance between CANH and CANL ≈ 60 Ω (two 120 Ω terminators in parallel)
Module supply voltage: battery voltage (~12–14 V) present at module power pin with key ON
Module ground continuity: low resistance to chassis ground (typically
Expected CAN message presence: brake booster should transmit periodic frames (typically several Hz to tens of Hz depending on vehicle); absence indicates no transmission

Diagnostic algorithm

Retrieve and record all codes and freeze frame data with a scan tool. Note whether module B is listed on the network scan.
Clear codes and attempt to re-establish communication. Re-check if U025F returns immediately or intermittently.
Inspect connector at Electronic Brake Booster Control Module B for corrosion, bent pins, water, or heat damage; repair as needed.
Verify power: back-probe the module power feed(s) with key ON; check fuses/relays that supply the module.
Verify ground: measure resistance from module ground pin to chassis/power negative; repair high-resistance grounds.
Check CAN physical layer: measure CANH and CANL voltages at the module connector and compare to a known-good node.
Check termination: measure DC resistance between CANH and CANL; replace missing/failed terminators or repair wiring if not ~60 Ω.
Monitor CAN traffic with a scan tool or oscilloscope while actuating wiring and connectors (wiggle test) to find intermittent opens/shorts.
If physical layer is OK but no module frames are present, try swapping or connecting to a known-good spare module (if available) or check upstream modules that wake/route messages.
Check for software updates or reprogramming requirements for the brake booster module and related network ECUs; perform reflash if manufacturer bulletins advise.
If wiring, power, ground, and bus are verified good and communication is still absent, consider replacing the Electronic Brake Booster Control Module B following proper programming and calibration procedures.
After repair, clear codes and perform a road test / function test to confirm the fault does not return.