U0174 – Lost Communication With Control Module “D”

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

Definition source: SAE J2012/J2012DA (industry standard)

U0174 indicates the vehicle network has detected a loss of communication with Control Module “D.” In plain terms, one or more other modules expected to see messages from that module over the communication network, but those messages were missing for longer than the monitor allows. Because network architecture, module naming, and monitoring strategy vary by vehicle, the exact identity and role of “Control Module D” can differ, as can the conditions that set the code and what features are affected. Use the scan tool’s module list, network topology information, and the factory service information for your specific vehicle to confirm which module is designated “D,” which network it’s on, and what prerequisites must be met for U0174 to run and fail.

What Does U0174 Mean?

U0174 – Lost Communication With Control Module “D” means the vehicle has logged a network communication fault where Control Module “D” is not communicating as expected. The code is set when other modules (or a central gateway, depending on design) do not receive required periodic messages from that module on the vehicle communication bus. SAE J2012 defines the standardized DTC structure, and for this DTC the fault is specifically about missing network communication—not a direct sensor “high/low” signal condition. The underlying reason can range from the module being offline (power/ground issue) to a network wiring/connector problem or an internal module/network interface fault.

Quick Reference

• Subsystem: Vehicle communication network (module-to-module data bus) involving Control Module “D”
• Common triggers: Module “D” stops transmitting, bus disruption, intermittent connection, or network isolation by a gateway
• Likely root-cause buckets: Wiring/connector issues, bus short/open, power/ground to module “D,” module fault, configuration/software issues (varies by vehicle)
• Severity: Varies; may be minimal or may disable features that depend on module “D” and can trigger warning indicators
• First checks: Verify which module is “D,” confirm if it’s online in the scan tool, check related fuses/power/grounds, and inspect network connectors for looseness/corrosion
• Common mistakes: Replacing the suspected module before confirming power/ground integrity and verifying the network is healthy at the connector

Theory of Operation

Modern vehicles use a shared communication network so control modules can exchange data and coordinate functions. Each module typically transmits identification and operating messages at defined intervals. Other modules may require these messages to operate correctly, and a gateway (if equipped) may route messages between network segments.

U0174 sets when expected messages from Control Module “D” are not received within an allowed time window. The monitoring module may also use additional criteria—such as ignition state, wake-up status, or network sleep/awake transitions—before it declares the loss of communication. If the module is powered down, has a poor ground, is disconnected, or if the network wiring is shorted/open, the message stream can stop or become unreadable, leading to a logged loss-of-communication fault.

Symptoms

• Warning lights illuminated on the instrument cluster (varies by vehicle and affected system)
• Multiple DTCs including other U-codes that indicate broader network communication issues
• Feature loss of functions that depend on Control Module “D” (capabilities vary by vehicle)
• Intermittent operation where symptoms appear during vibration, bumps, or temperature changes
• No communication with Control Module “D” when attempting to access it with a scan tool
• Reduced functionality such as limited mode operation if a dependent module defaults due to missing data

Common Causes

• Open circuit, short-to-ground, or short-to-power on the network communication lines between modules
• High resistance or intermittent connection at network-related connectors (loose terminal fit, fretting, pin damage, incomplete seating)
• Poor power feed to Control Module “D” (blown fuse, faulty relay, high resistance in the power supply circuit)
• Poor ground path for Control Module “D” (loose ground fastener, corrosion at ground point, damaged ground wire)
• Network backbone or splice/junction fault (damaged splice pack, bent pins at a gateway/junction, compromised harness segment)
• Control Module “D” reset/brownout due to unstable supply voltage (intermittent power/ground causing repeated reboots)
• Internal fault in Control Module “D” (hardware failure) after power/ground and network integrity are confirmed
• Configuration/software issue or incorrect module setup after replacement/programming (varies by vehicle; verify with service information)

Diagnosis Steps

Tools typically needed include a scan tool capable of full-network scans (and viewing module status), a digital multimeter, and access to vehicle-specific wiring diagrams and connector views. Helpful extras include back-probing leads, terminal test probes, and a battery support/charger for stable voltage during testing. If available, use a breakout/junction test method approved by service information to avoid terminal damage.

1. Verify the code and capture context: perform a full DTC scan of all modules, record U0174 and any companion network, power-supply, or ignition-related codes, and save freeze-frame or event data if the platform provides it.
2. Confirm which module is “Control Module ‘D’” for this vehicle: use service information to identify the physical location, connector IDs, and which network (or networks) it communicates on. Do not assume the module’s identity varies by vehicle.
3. Check whether the scan tool can communicate with Control Module “D”: attempt a direct connection to that module. Note whether it is completely non-responsive, intermittently present, or present with limited data, since each pattern points to different failure modes.
4. Assess network health at a high level: use the scan tool network topology/status (if supported) to identify additional modules reporting “lost communication” or “bus off” conditions. Multiple modules offline often indicates a backbone, power distribution, or gateway issue rather than a single module fault.
5. Perform a basic power supply inspection first: with key off, check fuses feeding Control Module “D” (both constant and switched, if applicable) and inspect related relays for signs of overheating or poor contact. Replace only if testing indicates an open or high resistance condition.
6. Verify power and ground at the module connector: using wiring diagrams, test for the presence of required power feeds and ground integrity at the correct pins. Use voltage-drop testing on grounds and on the power feed under load (as directed by service information) to detect hidden resistance that a simple continuity test can miss.
7. Inspect connectors and harness routing: disconnect the module connector(s) as appropriate and inspect for corrosion, moisture intrusion, bent or backed-out terminals, spread terminals, and damaged seals. Confirm connectors are fully seated and latched; correct any pin-fit issues found.
8. Check the communication circuit integrity: with the module disconnected (and following service information precautions), test the network circuits for opens/shorts between the module connector and the next harness junction/splice/gateway. Look for shorts to ground, shorts to power, and opens/high resistance in each communication line.
9. Perform a wiggle test with live monitoring: reconnect components, then monitor network status/PIDs and module presence on the scan tool while gently flexing the harness, tapping connectors, and moving harness segments near known stress points. If U0174 or module dropouts correlate with movement, isolate the exact segment/connector causing the interruption.
10. Isolate by segment if needed: if the network architecture allows, disconnect suspect branches one at a time (per service information) to see whether bus stability returns. This can help distinguish a harness/connector fault from a module that is loading the network or intermittently dropping offline.
11. Confirm the repair with a controlled drive cycle: clear DTCs, then perform an ignition cycle and road test while logging module communication status and relevant network PIDs. Re-scan all modules afterward to ensure U0174 and any related codes do not return.

Professional tip: Treat U0174 as a communication symptom, not a parts verdict. Prioritize proving stable power and ground to Control Module “D” and verifying network circuit integrity before considering module replacement. Intermittent U-codes are often caused by small voltage drops at grounds, poor terminal tension, or harness movement; live-data logging during a wiggle test is one of the fastest ways to turn an intermittent “lost communication” into a repeatable, measurable fault.

Possible Fixes & Repair Costs

Repair cost can vary widely because U0174 is a network communication fault and the correct fix depends on confirming where communication is being lost, whether power/ground is stable, and whether the issue is wiring, connectors, or the Control Module “D” itself.

• Repair or replace damaged wiring in the network circuits to Control Module “D” after pinpoint testing confirms opens, shorts, or high resistance.
• Clean, tighten, and reseat connectors at the module and any in-line junctions; repair poor pin fit, corrosion, or fretting only where verified.
• Restore module power and ground integrity by repairing blown feeds, loose grounds, poor splices, or high-resistance connections confirmed by voltage-drop testing.
• Address network backbone issues (e.g., faulty junction/connector points, damaged harness sections) when multiple modules show related communication DTCs.
• Update or reprogram a module only if service information indicates a calibration-related communication issue and testing shows wiring and power/grounds are stable.
• Replace Control Module “D” only after confirming correct power/ground, intact network wiring, and no external network fault pulling the bus down.

Can I Still Drive With U0174?

Sometimes the vehicle may still be drivable, but U0174 means a control module is not communicating, and the impact depends on what functions are managed by Control Module “D” (varies by vehicle). If you have warning indicators related to braking, steering, stability control, shifting, reduced power, stalling, or a no-start condition, do not continue driving; have the vehicle inspected and repaired. If drivability feels normal and no safety-related warnings are present, drive cautiously and avoid long trips until the communication fault is diagnosed.

What Happens If You Ignore U0174?

Ignoring U0174 can lead to intermittent or progressive loss of features controlled by the non-communicating module, unpredictable warning lights, degraded driver-assistance or stability functions (if equipped), and potential no-start events if communication becomes completely unavailable. A network fault can also complicate future diagnostics because multiple modules may set secondary codes when they lose data they expect to receive.

Last updated: March 17, 2026

Vehicles Commonly Affected by U0174

• Vehicles with multiple networked control modules where critical functions depend on shared data messages.
• Vehicles using a high-speed communication backbone with multiple branches to distributed modules.
• Vehicles with modules located in moisture-prone areas (low mounting points, wheelhouse areas, or near body seams) depending on design.
• Vehicles with prior electrical repairs where harness routing, splices, or connector pin fit may have been disturbed.
• Vehicles with recent battery events (low voltage, jump starting, battery replacement) that can expose weak connections.
• Vehicles used in harsh environments where vibration, heat cycling, or contamination can accelerate connector/wiring wear.
• Vehicles with add-on electrical loads that may introduce wiring stress or poor grounding if not integrated correctly.
• High-mileage vehicles where harness flex points and ground connections are more likely to develop resistance.

Always verify connector condition, power/ground stability, and network integrity with service information for the specific vehicle before considering programming or module replacement.