U011A – Lost Communication With Drive Motor Control Module “B”

System: Network | Standard: ISO/SAE Controlled | Fault type: General | Location: Designator B

Definition source: SAE J2012/J2012DA (industry standard)

DTC U011A indicates that one or more control modules on the vehicle network have detected a loss of communication with Drive Motor Control Module “B”. This is a network-level fault, meaning the problem is typically related to how modules exchange messages rather than a single sensor value being out of range. Depending on vehicle design, the drive motor control function may be split across multiple modules, and “B” identifies a specific module instance used by that platform. Because module naming, network layout, and monitoring strategy vary by vehicle, always confirm the exact module location, connector views, power/ground distribution, and diagnostic routines using the appropriate service information before testing or replacing parts.

What Does U011A Mean?

U011A – Lost Communication With Drive Motor Control Module “B” means the vehicle’s communication network is not receiving the expected messages from Drive Motor Control Module “B”, or other modules cannot establish/maintain valid communication with it. The code does not, by itself, prove the drive motor control module has failed; it only indicates that communication has been lost as detected by the network monitoring logic. In practice, this can occur if the module is unpowered, has a poor ground, is disconnected, has network circuit faults, or is present but unable to communicate due to internal or software-related issues. Diagnosis should focus on verifying module power/grounds and network integrity first.

Quick Reference

  • Subsystem: Vehicle network communications involving Drive Motor Control Module “B”
  • Common triggers: Module “B” stops transmitting required messages; network bus disrupted; module resets or powers down unexpectedly
  • Likely root-cause buckets: Power/ground to module, wiring/connector issues, network bus faults, module internal fault, configuration/software (varies by vehicle)
  • Severity: Often high; may cause reduced propulsion capability, no-start, warnings, or protective shutdown depending on system strategy
  • First checks: Scan for companion U-codes; confirm module “B” is present on the scan tool; check fuses/feeds/grounds; quick harness and connector inspection
  • Common mistakes: Replacing the module before verifying power/ground and network wiring; ignoring other network DTCs that point to the true fault location

Theory of Operation

Modern vehicles use a shared communication network so control modules can exchange status and commands. Drive Motor Control Module “B” typically broadcasts periodic messages such as operational state, self-diagnostics, and requested/actual control information. Other modules monitor these messages to coordinate propulsion functions and to verify that the module is alive and communicating correctly.

The loss-of-communication monitor generally sets when expected messages from module “B” are missing for a calibrated time, or when the network reports an error state that prevents message reception. The root cause is commonly that the module is not powered up, has unstable power or ground, or that the network circuits (including connectors, splices, and terminals) are open/shorted/high resistance. Less commonly, the module may be present but unable to communicate due to internal faults or configuration issues.

Symptoms

  • Warning lights: Malfunction indicator or system warning messages related to propulsion/network
  • Reduced power: Limited acceleration or a restricted operating mode
  • No-start: Vehicle may not enable drive/ready mode depending on architecture
  • Intermittent operation: Symptoms may come and go with vibration, temperature, or harness movement
  • Multiple codes: Additional network U-codes or module-specific communication faults stored in other modules
  • Inoperative functions: Features relying on drive motor control status may be disabled
  • Cluster messages: Communication or system fault notifications displayed to the driver

Common Causes

  • Open circuit, short-to-power, or short-to-ground on the network communication wiring between modules (network topology varies by vehicle)
  • High resistance in network wiring due to corrosion, damaged insulation, pin fit issues, or partially backed-out terminals at a connector
  • Poor power feed to Drive Motor Control Module “B” (blown fuse, faulty relay, weak splice, or excessive voltage drop under load)
  • Poor ground path for Drive Motor Control Module “B” (loose fastener, corroded ground eyelet, damaged ground wire, or excessive ground-side voltage drop)
  • Connector problems at Drive Motor Control Module “B” (water intrusion, bent pins, fretting, or improper seating/lock engagement)
  • Drive Motor Control Module “B” not booting or resetting due to internal fault or software/calibration issue (confirm only after power/ground and network checks pass)
  • Another module or network component degrading bus integrity (a single faulty node, connector, or harness section can disrupt communication and trigger “lost communication” codes)
  • Recent repairs or modifications that disturbed harness routing, shielding, or connectors (pinched harness, swapped connectors, incorrect terminal repair)

Diagnosis Steps

Tools typically needed include a scan tool capable of reading network DTCs and module status, a digital multimeter for power/ground and voltage-drop testing, and access to vehicle-specific wiring diagrams and connector views. A breakout lead set or back-probing tools can help avoid terminal damage. If available, use a data logger function on the scan tool to capture intermittent communication dropouts.

  1. Confirm the complaint and capture a full scan: Perform a complete vehicle scan and record all DTCs, including pending and history. Save freeze-frame or event data where available. Note which modules report U011A and whether the Drive Motor Control Module “B” appears in the module list.
  2. Check whether the module is reachable: Attempt to communicate directly with Drive Motor Control Module “B” using the scan tool. If it will not connect, treat the issue as a potential power/ground/module offline condition or a network physical-layer problem. If it connects, treat it as intermittent or network quality related.
  3. Assess related network and power DTCs first: Look for other communication, bus-off, voltage supply, or ignition feed codes. Diagnose those that indicate a broader network or power supply problem before focusing narrowly on U011A, since multiple modules can be affected by one root cause.
  4. Perform a visual inspection of the most likely areas: With the ignition off and key removed as required by the service procedure, inspect the Drive Motor Control Module “B” connector(s), nearby harness routing, and known flex points. Look for loose locks, water intrusion, corrosion, chafing, pinch points, or evidence of prior repairs.
  5. Check fuses/relays feeding the module: Using service information, identify all battery, ignition, and wake-up feeds to Drive Motor Control Module “B”. Verify fuses are intact and that relays operate correctly. Do not rely on visual inspection alone—confirm the circuit can carry load per the service procedure.
  6. Verify power and ground integrity with voltage-drop testing: Back-probe the module power and ground circuits (or use approved test points). Measure voltage drop on the power feed(s) and ground return(s) while the circuit is loaded (varies by vehicle; follow service info). Excessive drop indicates resistance in wiring, connections, splices, fuse/relay contacts, or grounds.
  7. Inspect and test the network wiring to the module: Identify the communication pair/wires used by the vehicle’s network for this module. Check for opens and shorts between the module connector and the next junction/connector. If service information allows, check for shorts to power/ground and wire-to-wire shorts. Repair any wiring damage using approved terminal and splice methods.
  8. Wiggle test for intermittents: With the scan tool monitoring module communication status and network-related PIDs, gently wiggle the harness and connectors along the route to Drive Motor Control Module “B” and at intermediate connectors. Watch for communication dropouts, status changes, or new DTC setting that correlates with movement.
  9. Evaluate network stability using live data/logging: If the module is intermittently reachable, run a drive/idle test while logging network health indicators available on the scan tool (module online status, communication error counters, or bus state where supported). Correlate any dropouts with conditions such as vibration, temperature, or electrical loads.
  10. Isolate the fault if the network is being pulled down: If symptoms suggest a network integrity issue, follow the vehicle’s network isolation procedure (varies by vehicle). This may involve disconnecting suspected nodes/sections one at a time to identify whether a specific connector, harness segment, or module is disrupting communication. Always power down and observe required wait times before disconnecting modules.
  11. Confirm the fix and prevent repeat failures: After repairs, clear DTCs and repeat a full scan. Verify Drive Motor Control Module “B” remains consistently online through multiple key cycles and under similar conditions that originally triggered the code. Recheck connector seating, harness retention, and routing to prevent chafe and strain.

Professional tip: If Drive Motor Control Module “B” is not reachable, prioritize power/ground voltage-drop testing before deeper network diagnostics. A module that is undervoltage, losing ground, or repeatedly resetting can mimic a network failure and trigger “lost communication” across multiple controllers. Proving stable power and grounds under load often prevents unnecessary network disassembly and avoids incorrect module replacement.

Need network wiring diagrams and module connector views?

Communication stop and network faults require module connector pinouts, bus wiring routes, and power/ground diagrams. A repair manual helps you trace the exact circuit path before replacing any ECU.

Factory repair manual access for U011A

Check repair manual access

Possible Fixes & Repair Costs

Repair costs for U011A vary widely because the fix depends on which part of the communication path failed and how accessible components are. Accurate diagnosis first helps avoid unnecessary module replacement, repeat failures, and additional labor from rechecks.

  • Restore power and ground to Drive Motor Control Module “B” by repairing the affected feed, fuse, relay, ground point, or high-resistance connection found during testing
  • Repair CAN/network wiring faults (open circuit, short-to-ground, short-to-power, or excessive resistance) between the module and the network backbone
  • Clean, reseat, or replace damaged connectors/terminals (spread pins, corrosion, moisture intrusion, weak pin fit) at the module or network junction points
  • Repair harness routing issues (chafing, pinch points, heat damage) and add proper protection/retention to prevent recurrence
  • Perform required module setup actions after repairs when applicable (configuration, relearn, or initialization varies by vehicle and service information)
  • Update or reprogram control modules only if service information confirms a software-related communication concern and power/network integrity is verified
  • Replace Drive Motor Control Module “B” only after confirming power/ground integrity and network wiring are correct and communication remains lost

Can I Still Drive With U011A?

U011A indicates lost communication with Drive Motor Control Module “B,” so drivability impact can range from minimal to severe depending on vehicle design and what functions that module supports. If the vehicle enters reduced-power mode, will not start, stalls, or shows warnings related to propulsion, braking, or steering, do not continue driving—have it inspected and towed if needed. If it drives normally, limit use, avoid high-demand conditions, and verify the fault does not return while you arrange diagnosis.

What Happens If You Ignore U011A?

Ignoring U011A can lead to intermittent or worsening loss of propulsion-related functions, unexpected reduced power, recurring warning indicators, and repeated communication dropouts that may affect other modules on the network. A progressing wiring or connection issue can become a no-start condition, increase diagnostic complexity, and potentially cause secondary faults as modules lose data needed for coordinated control.

Compare nearby lost drive trouble codes with similar definitions, fault patterns, and diagnostic paths.

  • U011E – Lost Communication With Motor Control Module "E"
  • U011D – Lost Communication With Motor Control Module "D"
  • U017D – Lost Communication With Control Module “M”
  • U017C – Lost Communication With Control Module “L”
  • U017B – Lost Communication With Control Module “K”
  • U017A – Lost Communication With Control Module “J”

Key Takeaways

  • U011A means the vehicle detected lost communication with Drive Motor Control Module “B,” not a confirmed failed module.
  • The most common fault areas are power/ground feeds, connectors/terminals, and CAN/network wiring integrity.
  • Diagnose with test-driven checks: verify power/grounds, inspect connectors, and prove network continuity before replacing modules.
  • Severity varies by vehicle; reduced power, stalling, or no-start conditions warrant stopping driving and arranging service.
  • Fix the verified cause, then confirm stable communication by clearing codes and rechecking under similar operating conditions.

Vehicles Commonly Affected by U011A

  • Vehicles equipped with multiple drive motor control modules (for example, dual-motor or multi-axle propulsion architectures)
  • Hybrid and electric vehicles that rely heavily on network messaging for propulsion coordination
  • Vehicles with complex CAN network topologies and multiple gateways
  • Vehicles operated in high-vibration environments that can stress harness routing and connector pin fit
  • Vehicles exposed to moisture, road spray, or temperature cycling that can accelerate connector corrosion
  • Vehicles with prior collision or underbody repairs where harness routing or retention may have been disturbed
  • Vehicles with recent electrical work (battery service, harness repairs, module replacement) where connectors may be partially seated
  • High-mileage vehicles where harness insulation and terminal tension may degrade over time

FAQ

Does U011A automatically mean Drive Motor Control Module “B” is bad?

No. U011A only indicates that communication with Drive Motor Control Module “B” was lost. The root cause is often power/ground loss, connector/terminal problems, or a network wiring fault. Replace the module only after those fundamentals test good and communication is still missing.

Why does U011A come and go?

Intermittent U011A is commonly caused by marginal connections: loose or contaminated terminals, harness chafing that occasionally shorts or opens with movement, or unstable power/ground. Heat, vibration, and moisture can change resistance enough to make the fault appear and disappear.

Can a weak battery or poor ground cause U011A?

Yes. If module supply voltage drops or a ground path develops high resistance, the module may reset or drop off the network, which other modules can interpret as lost communication. Confirm battery condition and perform voltage-drop testing on the module’s power and ground circuits per service information.

Will clearing the code fix U011A?

Clearing codes only removes stored fault memory; it does not repair the underlying cause. If the communication problem is still present, U011A will typically reset quickly or after a similar drive cycle. Use clearing only after completing repairs and then verify the fix with a recheck.

What should be checked first for U011A?

Start with the basics: verify module power and ground integrity, inspect and reseat connectors at Drive Motor Control Module “B,” and check the network wiring near common stress points for damage or corrosion. If those checks pass, move to deeper network diagnostics and confirm whether communication is missing at the scan tool.

For any repair, confirm the fix by verifying stable communication with Drive Motor Control Module “B,” clearing stored codes, and rechecking after an operating period similar to when U011A originally set.