OBD-II Code U1624: Lost Communication With Telematics Control Module

What Does U1624 Mean?

Code U1624 means your vehicle's main computer lost its communication link with the Telematics Control Module (TCM). The TCM is the central hub for external communication, running services like OnStar, emergency calling, GPS navigation, and in-vehicle Wi-Fi. When this data connection drops, these features fail and the U1624 code stores in other network modules.

Technical definition: The SAE/ISO definition for U1624 is 'Lost Communication with Telematic Control Module on Ethernet B'. This indicates a data network failure linking the telematics unit to other critical computer modules, such as the image processing module or main gateway.

Can I Drive With U1624?

Yes, But With Caution. From a mechanical standpoint, the vehicle is safe to drive; core functions like steering, braking, and acceleration remain unaffected. However, critical features like automatic emergency calling (OnStar, eCall) and real-time GPS location services will be inoperative. In a crash, your vehicle cannot automatically summon help, and advanced driver-assistance systems like GM's Super Cruise are disabled.

Common Causes

• Telematics Control Module Software/Firmware Glitch (Very Common) — On 2024+ General Motors vehicles, a known software bug prevents the module from communicating. Manufacturers issued multiple technical service bulletins (TSBs) advising dealerships to perform a software update rather than replace hardware.
• Failed Over-the-Air (OTA) or Mapping Update (Common) — A map or system OTA update failing to install correctly crashes the telematics module. This often happens if the vehicle battery voltage drops too low during the update process.
• Temporary Head Unit Freeze/Crash (Common) — The infotainment or telematics system crashes like a personal computer. A 'soft reset' of the head unit often restores communication and clears the code without parts replacement.
• Faulty Telematics Control Module (TCM) (Common) — The module fails internally due to a short circuit or component degradation, permanently severing its network connection.
• Low Battery Voltage or Poor Ground Connection (Less Common) — Computer modules require stable voltage. A weak battery (under 12.4V) or failing alternator causes unpredictable communication errors across the network.
• Damaged Wiring or Loose Connectors (Less Common) — Vibration, moisture, or physical impact damages the automotive Ethernet wires connecting the TCM. Loose connectors cause intermittent communication loss.
• Blown Fuse for TCM (Rare) — A blown dedicated power fuse completely kills power to the TCM, triggering U1624 in other modules trying to reach it.

Symptoms

• 'Super Cruise Unavailable' or 'Adaptive Cruise Unavailable' Message — For GM vehicles, this warning appears immediately on the driver information center.
• Loss of OnStar, Wi-Fi, GPS, and App Features — The OnStar status light turns red or off, the Wi-Fi hotspot drops, navigation loses GPS lock, and remote smartphone apps fail to connect.
• 'Service Emergency Calling' Message — A dashboard warning indicates the automated eCall system is offline.
• Check Engine Light is On — The Malfunction Indicator Lamp illuminates to alert the driver of the stored network fault.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this code.

Common Fixes & Costs

• Dealership Software Update — Parts: $0, Labor: $150-$300, ~1.5 hr book time (Professional)
• Perform Head Unit 'Soft Reset' — Parts: $0, Labor: $0, ~0.1 hr book time (DIY)
• Clean or Tighten Battery Connections — Parts: $0-$10, Labor: $0, ~0.2 hr book time (DIY)
• Replace Telematics Control Module (TCM) — Parts: $500-$800, Labor: $200-$500, ~2.5 hr book time (Professional)
• Repair Damaged Network Wiring — Parts: $5-$20, Labor: $200-$600, ~4.0 hr book time (Professional)

Used vs. New Parts: Buying Guide

When a used part is worth it: Consider a used TCM only if the vehicle is out of warranty, the budget is tight, and a new part is on long-term backorder.

Donor-vehicle mileage cap: roughly under 60000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Match the part number exactly.
• Verify the used part is not from a flood-damaged vehicle.
• Ensure the seller has a return policy for programming failures.

Decision logic:

• If Vehicle is under warranty → Use a new OEM part installed by the dealer. The repair is free.
• If The known fix is a software update → A used part will not help. The vehicle needs the dealership software service.
• If Vehicle is out of warranty and a new part is over $700 → A used part is a high-risk option. You must find a shop willing to program a used module.

Warranty tradeoff: Used parts typically have a 30-day warranty covering the part only. New OEM parts installed by a dealer come with a 12-24 month parts and labor warranty.

Worst-case if a used part fails: $500-$1000 if a used module cannot be programmed or fails after installation.

What Happens If You Wait — Timeline

1. Immediate: Code U1624 is stored. 'Super Cruise Unavailable' and 'Service Emergency Calling System' messages appear. Check Engine Light illuminates. (MPG impact: 0%% · Added cost: $0)
2. First week: All telematics-based features are confirmed inoperative, including automatic crash response, remote start via app, and real-time GPS navigation. (MPG impact: 0%% · Added cost: $0)
3. 1-3 months: The vehicle fails its annual state emissions/safety inspection due to the illuminated Check Engine Light, preventing registration renewal. (MPG impact: 0%% · Added cost: $50-$300 in potential fines, late fees, or re-inspection costs.)
4. 3+ months: The fault becomes a permanent condition, significantly reducing the vehicle's resale or trade-in value due to a known, unresolved electronic fault. (MPG impact: 0%% · Added cost: $1000+ in diminished resale value.)

Cost of Not Fixing It

• Immediate: Loss of Automatic Crash Response and Super Cruise. (Added cost: $0)
• 0-3 months: Failure to pass state emissions/safety inspections due to the active Check Engine Light. (Added cost: $50-$300 in potential fines, late fees, or re-inspection costs.)
• 3+ months: Permanent loss of built-in features and significant reduction in vehicle resale value. (Added cost: $1000+ in diminished resale value.)

Diagnosis Steps

1. Check for Technical Service Bulletins (TSBs)
   Search online for TSBs related to your vehicle's year, make, model, and U1624. For 2024+ GM vehicles, reference TSBs like PIT6186E or PIC6557D to confirm a software update is the required fix.
   Tools: Computer with internet access (Beginner)
2. Read All Stored Trouble Codes
   Use a full-system OBD-II scanner to read codes from all modules. A solitary U1624 points to the TCM; multiple 'U' codes (like U023B) confirm a wider network software bug.
   Tools: Professional OBD-II Scanner (Beginner)
3. Inspect Battery Voltage
   Check the main battery voltage with a multimeter. A healthy battery reads 12.4-12.6 volts with the engine off, and 13.7-14.7 volts running. Voltages below these ranges trigger random communication codes.
   Tools: Multimeter (Beginner)
4. Perform Head Unit Soft Reset
   Hold the radio power button for 15 seconds or press the recessed reset pinhole. This forces the telematics system to reboot and clears temporary software freezes.
   Tools: Paperclip (optional) (Beginner)
5. Locate and Inspect the TCM
   Find the TCM (often behind the glove box or headliner). Unplug and replug the connectors to ensure a solid connection and check for corroded pins.
   Tools: Trim removal tools, flashlight (Intermediate)
6. Check Power and Ground
   Using a wiring diagram, probe the TCM's power and ground pins. Verify 12V+ with the key on and less than 0.5 ohms of resistance on the ground circuit.
   Tools: Multimeter, vehicle-specific wiring diagram (Advanced)
7. Monitor Live Data PIDs
   Navigate to the Gateway Module live data on a scan tool. Check the TCM 'Module Status'. If it reads 'Offline' despite having good power and ground, the module or network wiring has failed.
   Tools: Professional OBD-II Scanner (Advanced)
8. Check Network Activity
   Connect an oscilloscope to the Ethernet B data lines. A distinct square wave proves the network is physically intact, while a flat line indicates a broken wire or dead module.
   Tools: Oscilloscope, back-probe connectors (Professional)

When This Code Triggers (Freeze-Frame Conditions)

• System Voltage: 13.5-14.5V (Engine running, stable charging system)
• Vehicle Speed: 35-65 mph (Steady highway or city driving)
• Engine RPM: 1200-2500 RPM (Cruise or steady throttle application)
• Time Since Engine Start: > 5 minutes (Vehicle has been running long enough for network self-tests to complete)

Related Codes

• U023B — Lost Communication with Image Processing Module B. Often appears with U1624 during system-wide Super Cruise software crashes.
• U053C — Invalid Data Received from Image Processing Module. Indicates the module is online but sending corrupt data; treat as a system-wide software fault if paired with U1624.
• U3000 — Control Module Failure. Stored inside the TCM itself, confirming internal hardware failure rather than a network issue.
• U164E — Lost Communication with GPS Module. Points specifically to the GPS partition of the telematics unit failing.

Climate & Environmental Factors

• High Humidity: Accelerates corrosion on the TCM's external connectors and internal circuit board traces, leading to short circuits.
• Extreme Cold: Reduces battery efficiency, causing low system voltage during startup which triggers temporary communication errors.
• Extreme Heat: Causes thermal stress on internal TCM solder joints, creating microscopic cracks and intermittent open circuits.

How to Talk to a Mechanic About This Code

Say this: "I'm scheduling a diagnostic appointment for a U1624 code on my [Year, Make, Model]. I've read this is frequently caused by a software issue on these vehicles, so could you please check for any relevant Technical Service Bulletins, like PIC6557D or PIT6186E, as a first step?"

This signals you are an informed customer, directs the technician to the most probable solution first, and prevents an immediate recommendation for an expensive module replacement.

Avoid saying:

• 'Just fix whatever's wrong'
• 'My check engine light is on, can you look at it?'
• 'Whatever you recommend'

Questions to ask before authorizing the repair:

• Did you find any Technical Service Bulletins (TSBs) for this code on my vehicle's VIN?
• If you're recommending a module replacement, what specific test confirmed the hardware has failed? Did you find a U3000 code in the module itself?
• Is this repair covered under the bumper-to-bumper or any other active warranty?
• If the fix is a software update and the vehicle is out of warranty, what is the estimated labor time and cost?

Where to Take It: Dealer vs Independent vs Chain

• Dealer: Strongly Recommended. The most common fix for U1624 on newer cars is a software update that only a dealer can perform.
  Best for: Vehicles under warranty (the repair will be free), 2022+ GM, Ford, or other modern vehicles where a software update is the most likely fix, Complex network diagnostics requiring proprietary manufacturer software
  Downsides: Higher labor rates (typically 1.5-2x vs. independent shops), May suggest module replacement if not prompted to check TSBs first (Typical cost: +50% vs. baseline)
• Independent Shop: Acceptable for initial diagnosis on older vehicles. A good independent shop diagnoses power and wiring faults but sends you to the dealer if a software update is needed.
  Best for: Out-of-warranty vehicles where a wiring or connector issue is suspected, Older vehicles (pre-2018) where a software bug is less likely to be the cause
  Downsides: Cannot perform manufacturer-specific software updates., Lacks access to the very latest TSBs or advanced network diagnostic tools. (Typical cost: +0% vs. baseline)
• Chain Shop: AVOID. This type of fault is far outside the scope of work for a typical chain repair shop.
  Best for: Simple, unrelated maintenance like oil changes or tires
  Downsides: Not equipped for complex electronic or network diagnostics, Technicians lack the specialized training for this type of repair (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the estimated out-of-warranty repair cost exceeds 40-50% of the car's private-party value, seriously consider not fixing it.

• Car worth $45000, fix is $0: Fix it. The repair is covered under the new vehicle warranty.
• Car worth $20000, fix is $1300: Fix it. The repair cost is only 6.5% of the vehicle's value and restores critical safety and convenience features.
• Car worth $6000, fix is $1300: Borderline. The repair is ~22% of the car's value. Get a second opinion to confirm a module replacement is truly needed before proceeding.

What Scan Tool You Need for This Code

Minimum: A tool that performs a 'full system scan' to read codes from all vehicle modules, not just the engine computer.

A basic $20 code reader only checks the Engine Control Module. U1624 is a network fault seen by many modules. Seeing if other codes like U023B are present is critical for diagnosis.

Budget: Autel MaxiAP AP200 or OBDLink MX+ (~$80) — These Bluetooth dongles connect to your smartphone and scan all vehicle systems to give you a complete list of codes.

Mid-range: Foxwell NT510 Elite or similar (~$180) — Provides full system diagnostics plus bidirectional controls to see live data from specific modules.

Professional: Autel MaxiCOM MK808S or Launch X431 CRP919XBT (~$400-600) — Offers extensive bidirectional controls and full-system diagnostics to command specific modules and view detailed live data streams.

How to Clear the Code After You Fix It

1. Reconnect any disconnected components (battery, module)
2. Use a compatible OBD-II scan tool to perform the 'Clear All DTCs' command
3. Perform a complete GM drive cycle to allow readiness monitors to run.

Drive cycle (~20 minutes): From a cold start, idle for 3 minutes with electrical loads on. Accelerate to 55 mph and hold steady for 5 minutes. Coast down to 20 mph without braking. Accelerate again to 60 mph and hold steady for 5 minutes. Coast down again.

Readiness monitors affected: Catalyst monitor, O2 sensor monitor, EVAP system monitor

Before emissions retest: drive at least 50 miles to fully set monitors.

Watch out for:

• Disconnecting the battery will not clear permanent DTCs and resets all readiness monitors to 'Not Ready', guaranteeing an emissions test failure.
• The code returns immediately if the root cause is not fixed before clearing.
• Not completing the full drive cycle leaves monitors 'Not Ready', causing an emissions test failure.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: An illuminated Check Engine Light is an automatic failure. A permanent DTC requires driving up to 200 miles over 15 warm-up cycles before it clears the smog computer.
• New York: The OBD-II inspection is a required part of the annual safety inspection. An illuminated 'Check Engine' light causes an automatic failure.
• Texas: In the 17 counties requiring emissions testing, an illuminated Check Engine Light is an automatic failure. Clearing the code right before the test fails the vehicle for 'Not Ready' monitors.

Most Commonly Affected Vehicles

• GMC Yukon / Yukon XL (2022-2025) — Frequently reported in relation to Super Cruise and OnStar module failures.
• Chevrolet Silverado EV, Suburban, Tahoe, Traverse (2024-2026) — Subject to multiple NHTSA service bulletins for U1624 caused by a software glitch affecting Super Cruise.
• Cadillac Escalade, LYRIQ, CT5, CT4, OPTIQ (2024-2026) — Explicitly listed in GM service bulletins (PIC6557D, PIC6582) for the exact same software-related U1624 code.
• GMC Sierra EV, Acadia (2024-2026) — Included in the GM-wide TSBs regarding telematics and Super Cruise communication loss.
• Chevrolet Blazer EV, Equinox EV (2024-2025) — Specifically named in GM Preliminary Information bulletin PIC6557D as being affected by the software issue.
• Ford F-150, Explorer, Mustang Mach-E (2021-2024) — Ford's Telematics Control Unit (TCU) fails after OTA updates, causing loss of FordPass connectivity.

Manufacturer-Specific Notes

• General Motors (Chevrolet, GMC, Cadillac, Buick): For 2024-2026 models, U1624 is almost exclusively a software bug addressed by TSBs (PIC6557D, PIT6167G). Dealers are instructed to update software, not replace hardware.
• Ford: TCU issues frequently occur after OTA updates. Pulling the TCU fuse for 10 minutes forces a hard reset and often re-establishes server connection.
• Hyundai / Kia: Telematics (Blue Link/UVO) communication drops are often server-side outages. Check for known network outages before attempting vehicle repairs.
• BMW: iDrive telematics failures are often resolved by selecting 'Update apps and services' in the options menu to force a server refresh.

Real Owner Stories

2024 GMC Yukon XL Denali - 'Super Cruise Unavailable'

Super Cruise worked for two months, then the 'Super Cruise is unavailable' message appeared, triggering code U1624. OnStar and GPS functions were lost.

Outcome: The dealership advised the owner to wait until a software fix is developed. The vehicle was returned with features inoperative.

Lesson: For new vehicles with software faults, the fix depends on the manufacturer releasing a patch. Get the issue documented in writing to ensure warranty coverage.

2024 GMC Sierra Denali - Intermittent Camera and Super Cruise Failure

Shortly after purchase, all cameras and Super Cruise stopped working.

Outcome: The owner was left waiting indefinitely for a replacement module and began discussing a vehicle buy-back.

Lesson: If a critical feature fails on a brand-new vehicle and the part is unavailable, you have grounds for a lemon law claim or dealership buy-back.

Audi Q7 - 'Emergency System Malfunction'

An 'Emergency call system malfunction' warning appeared, indicating a telematics problem analogous to U1624.

Outcome: The technician cleaned the contacts and replaced the damaged wiring, restoring full functionality.

Lesson: Don't assume the module itself has failed. A thorough inspection of wiring and connectors reveals cheaper root causes like corrosion.

General Motors - Failed Over-the-Air (OTA) Update

An infotainment update failed to complete, preventing the telematics module from operating correctly.

Outcome: The next day, the vehicle automatically prompted to run the previously failed update, which completed successfully in minutes.

Lesson: If U1624 appears after a failed OTA update, fully charge the battery with an external charger to allow the update to complete.

How to Prevent This Code From Triggering

• Maintain Battery Health and Connections (Every 6 months) — Low voltage from a weak battery or loose terminals is a primary cause of communication module errors. Ensuring the battery is charged provides stable power.
• Accept and Install Over-the-Air (OTA) Software Updates Promptly (As they become available) — Manufacturers use OTA updates to fix software bugs that cause communication issues like U1624.
• Ensure a Strong Battery Charge Before Installing Updates (Before any major software update) — Vehicle software updates are blocked if the battery's state of charge is too low. Connecting a battery tender ensures it has enough power to complete.
• Keep Module Connectors and Interior Dry (Ongoing) — Moisture from humidity or a water leak causes corrosion on the pins of the Telematics Control Module's connector, leading to a loss of communication.
• Perform Periodic Scans with an OBD-II Tool (Annually) — Scanning for codes reveals intermittent or history codes, allowing for diagnosis before it becomes a persistent, feature-disabling fault.

Frequently Asked Questions

Can I fix the U1624 code myself?

Yes, if the cause is a low battery or a temporary glitch fixed by a radio reset. However, the most common cause on 2024+ vehicles is a software bug requiring proprietary dealership tools to update.

Is it safe to drive with the U1624 code?

Yes, the vehicle remains mechanically safe to drive, steer, and brake. You will, however, lose automatic emergency calling and advanced driver aids like Super Cruise.

Will clearing the code with my scanner fix the problem?

No. Clearing the code only turns off the check engine light temporarily. The code returns immediately because the underlying communication failure still exists.

The dealer wants to replace the module, what should I do?

Ask the service advisor to check for TSBs like PIC6557D or PIT6186E first. These bulletins explicitly instruct technicians to perform a software update instead of replacing expensive hardware.

Is this covered by warranty?

Yes. If your vehicle is within the bumper-to-bumper warranty period (typically 3 years/36,000 miles), the diagnosis and software update or module replacement is completely free.

Why did the dealer tell me to wait for a fix?

Manufacturers sometimes identify a software bug before the patch is ready. The dealer documents the fault to ensure it is covered under warranty once the software update is officially released.

Key Takeaways

• Code U1624 indicates the Telematics Control Module (responsible for OnStar and GPS) has stopped communicating with the vehicle's network.
• On 2024 and newer GM vehicles, a known software bug causes the majority of U1624 codes; check Technical Service Bulletins (like PIC6557D) before replacing parts.
• While mechanically safe to drive, U1624 disables critical safety features like automatic crash response and advanced driver aids like Super Cruise.
• Expect to pay $150 to $300 for a dealership software update if your vehicle is out of warranty, or $0 if covered under the 3-year/36,000-mile bumper-to-bumper warranty.