U0198 on 2015-2019 Lincoln MKZ: Lost Communication With TCU Causes and Fixes

What's Unique About the 2015-2019 Lincoln MKZ

For this generation of Lincoln MKZ and its platform mates like the Ford Fusion, the U0198 code is very specifically tied to the TCU and its software or cellular technology. Unlike in other vehicles where a communication code might point to widespread wiring failure, on the MKZ it's a well-documented issue often resolved without replacing any parts. Manufacturer Technical Service Bulletins (TSBs) point directly to software glitches and updates as the primary cause. Furthermore, the 2022 shutdown of 3G cellular networks rendered the TCUs in 2015-2017 models obsolete, making a hardware upgrade to a 4G unit a common and necessary fix.

Diagnostic Flowchart

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

Symptoms You May Notice

• Lincoln Way app remote features are inoperative (remote start, lock, unlock, vehicle location).
• A message about 'incomplete user authorization' appears on the infotainment screen.
• The modem's Electronic Serial Number (ESN) is missing or blank in the APIM's 'About' settings screen.
• The SOS or telematics warning light may be illuminated on the dashboard.
• The Lincoln Way app fails to update vehicle status like fuel level or location.
• A 'SOS System Fault' message may appear on the instrument cluster.

Most Likely Causes

1. TCU Software Glitch 🔴 High Probability The control modules in modern vehicles can occasionally lock up, similar to a frozen computer or smartphone. This is a known issue addressed by Lincoln TSBs SSM 48267 and SSM 49084.
   How to confirm: Performing a hard reset by pulling the TCU fuse is the easiest way to confirm. If functionality returns after the reset, a temporary glitch was the cause. This is the first step recommended in multiple TSBs.
   Typical fix: Turn the vehicle off, locate the TCU fuse (Fuse 79, a 10A fuse in the passenger compartment fuse panel for 2017+ models), remove it for at least 5 minutes, then reinstall it. This forces the module to reboot.
   Est. part cost: $0
2. Obsolete 3G TCU 🔴 High Probability Models from 2015-2017 were equipped with 3G TCUs. Major cellular carriers shut down their 3G networks in 2022, making these modules unable to connect and communicate, which can trigger a U0198 code.
   How to confirm: Check the vehicle's build date. If it's a 2015-2017 model, it almost certainly has a 3G TCU. A visual inspection of the module will show no external antenna ports, whereas a 4G unit has one or two round FAKRA connectors.
   Typical fix: The TCU must be upgraded to a 4G version. This involves replacing the module and adding a new 4G antenna. Lincoln offered a Customer Satisfaction Program (21B09) for this, but it expired in May 2022. The upgrade can be done by a dealer or an advanced DIYer with FORScan software.
   Est. part cost: $150-$600
3. Outdated TCU Software 🟡 Medium Probability Lincoln has issued Field Service Actions (FSAs) and TSBs (like SSM 47160) to update the TCU software to resolve communication bugs.
   How to confirm: A Lincoln dealer can check your vehicle's VIN for any open FSAs or applicable software updates. This is especially relevant if a fuse pull doesn't permanently solve the issue.
   Typical fix: A dealer reprograms the TCU with the latest software version using their diagnostic tools (IDS or FDRS).
   Est. part cost: $0 (if covered by FSA) or $100-$200 (dealer labor)
4. Failed Telematics Control Unit (TCU) ⚪ Low Probability While less common than software or obsolescence issues, the module itself can fail internally due to electronic component failure.
   How to confirm: If a fuse pull and software updates do not resolve the code, and the wiring is confirmed to be good, the module itself is the likely culprit. A diagnostic scan may also show a U3000: Control Module internal failure code.
   Typical fix: Replacement of the TCU. This is not a plug-and-play part and must be programmed to the vehicle by a dealer or a qualified technician with the correct tools.
   Est. part cost: $100-$500 (Used/Remanufactured)
5. Blown Fuse or Wiring Issue ⚪ Low Probability While not specific to this platform, any electrical module can lose power due to a blown fuse or a problem in the wiring harness (e.g., corrosion, damage).
   How to confirm: Visually inspect the TCU fuse (F79 in the passenger compartment panel). Use a multimeter to check for 12V power and a solid ground connection at the TCU's electrical connector in the trunk.
   Typical fix: Replace the blown fuse or repair the damaged section of the wiring harness.
   Est. part cost: $1-$100

Diagnosis Steps

1. Verify the symptoms: Check if remote features on the Lincoln Way app are working and check for a blank modem ESN in the vehicle's SYNC settings menu ('Settings' > 'General' > 'About SYNC').
2. Perform a hard reset: Locate the fuse for the Telematics Control Unit. On 2017-2019 models, this is Fuse 79 (10A) in the passenger compartment fuse panel. On 2015-2016 models, it is also in the passenger compartment panel. Remove the fuse for at least 5 minutes, then reinstall it. This procedure is recommended by TSB SSM 48267.
3. Check for 3G Obsolescence (2015-2017 models): If your car is in this year range, assume the 3G TCU is obsolete due to the 2022 network shutdown. The only permanent fix is upgrading to a 4G module.
4. Check for open recalls or TSBs: Contact a Lincoln dealer with your VIN to see if there are any Field Service Actions (FSAs) for the TCU, such as the expired Customer Satisfaction Program 21B09 for the 4G upgrade.
5. Apply Software Updates: If the reset does not work on a 4G-equipped vehicle, have a dealer perform any available TCU software updates as recommended by TSB SSM 47160.
6. Inspect Wiring: If the code persists, locate the TCU. On the MKZ, it is located in the trunk, behind the right-side trim panel/carpet. Visually inspect the connectors and wiring for any signs of damage, corrosion, or looseness.
7. Test Power and Ground: Using a multimeter, confirm that the TCU is receiving 12V power and has a solid ground connection at its harness connector.
8. Replace the TCU: If all previous steps fail, the TCU module has likely failed and needs to be replaced and programmed by a qualified technician or an advanced DIYer using software like FORScan.

Parts You'll Likely Need

• 4G Telematics Control Unit (TCU) (OEM #HJ5T-14G229-AN / K1GT-14G229-AL) — This is the required replacement for a failed TCU or an obsolete 3G unit. Part numbers starting with 'H', 'J', or 'K' are 4G modules; older 'G' series parts are 3G and should be avoided. The part must be programmed to the vehicle after installation.
  Trusted brands: Motorcraft, Visteon, Continental
  OEM price range: $400-$600
  Aftermarket price range: $100-$250 (Used/Remanufactured)
• FAKRA Cellular Antenna (OEM #HS7Z-19A390-A) — When upgrading from a 3G TCU (which has an internal antenna) to a 4G TCU, a separate external antenna is required.
  Trusted brands: Ford, Bingfu
  OEM price range: $30-$50
  Aftermarket price range: $10-$20

Related Codes That Often Appear With This One

• U3000: Control Module

Technical Service Bulletins (TSBs) & Recalls

• SSM 48267: Addresses inoperative remote features and DTC U0198, recommending the removal of the TCU fuse for 5 minutes to correct the condition.
• SSM 47160: For 2015-2017 models, advises performing any open Field Service Actions (software updates) for the TCU. If the code remains, it also recommends pulling the TCU fuse before attempting to reprogram the module.
• SSM 49084 / SSM 50726: Also addresses inoperative remote features and blank modem ESN, recommending the TCU fuse pull as the first step before reprogramming.
• Customer Satisfaction Program 21B09: A now-expired program to help owners of 2015-2017 vehicles upgrade their obsolete 3G TCU to a 4G unit.

Platform-Specific Known Issues

• The most significant issue is the 3G cellular network shutdown by carriers like AT&T in February 2022. This rendered the TCUs in all 2015-2017 Lincoln MKZ models permanently inoperable for connected services. Lincoln offered a temporary Customer Satisfaction Program (21B09) to subsidize the upgrade to a 4G modem, but this program expired on May 31, 2022, leaving many owners to cover the full cost of the necessary hardware upgrade.

Mechanic-Grade Diagnostic Values

• MS-CAN Bus Network Total Resistance — expected: ~60 Ω. Failure: A reading of ~120 Ω indicates one of the two terminating resistors is not seen by the network. A reading significantly different from 60 Ω or an open circuit (OL) points to a wiring issue.
• MS-CAN High Voltage (Key On, Engine Off) — expected: Fluctuates between ~2.5V (recessive) and ~3.5V (dominant) as messages are sent.. Failure: Stuck high, stuck low, or no voltage indicates a wiring short/open or a failed module transceiver.
• MS-CAN Low Voltage (Key On, Engine Off) — expected: Fluctuates between ~2.5V (recessive) and ~1.5V (dominant) as messages are sent.. Failure: Stuck high, stuck low, or no voltage indicates a wiring short/open or a failed module transceiver.
• TCU Ground Connection Resistance — expected: < 0.5 Ω. Failure: A reading higher than 0.5 Ω indicates a poor or corroded ground connection, which can cause intermittent module operation.

Hidden / Shadow Codes Worth Checking

• U0198:87: Lost Communication With Telematic Control Module: Missing Message. This extended code specifically indicates that the APIM is expecting a message from the TCU but is not receiving it, as opposed to a general electrical failure. (see via A professional scan tool or advanced DIY software like FORScan can read extended trouble code data.)

Scan Tool Commands That Help

• FORScan: TCU Firmware Update — Used when upgrading a TCU from a different vehicle model or year. For example, a firmware downgrade may be required when installing a newer 'K' series TCU into an older vehicle that came with an 'H' series.
• FORScan: TCU As-Built Configuration — Essential after replacing a 3G TCU with a 4G unit. The As-Built data from a VIN of a vehicle that originally came with a 4G modem must be written to the new module to enable all features.
• FORScan / Ford IDS: TCU Module Reset / Reboot — A software-forced reboot that can be attempted after programming changes or to resolve a temporary glitch, similar to a fuse pull.
• Ford IDS: Network Test — This is a guided diagnostic routine recommended by Ford TSBs (like SSM 47160) to verify communication between all modules on the network before and after programming.

Wiring & Ground Locations

• TCU Module — In the trunk, located behind the right-side trim panel/carpet.. This is the physical location of the module for inspection of connectors, part numbers, and performing voltage/ground tests at the harness.
• G100 / G102 — Left front of the engine compartment.. These are primary chassis ground points in the engine bay. While not the direct ground for the TCU, poor engine bay grounds can introduce electrical noise and issues throughout the vehicle.
• G201 — Left center of the dash, behind the instrument panel.. This is a major interior ground point. A problem here could affect multiple interior modules, including the APIM which sets the U0198 code.
• TCU Connector (C2403A/B) — The main electrical connector at the TCU module in the trunk.. This is where a technician would perform pin-out tests for power (Pin 1, typically a Violet/Red wire), ground (Pin 8, typically a Black/Yellow wire), and the MS-CAN network lines (e.g., Pin 12 CAN+ and Pin 13 CAN-).

Real Owner Repair Stories

• CyanLabs Forum User (2016 Lincoln MKZ 2.0L) — Upgraded from 3G to a 4G TCU (JL3T-14G087-CK). Lincoln Way app connected and showed vehicle status (mileage, oil life) but remote functions (start/stop) failed.
  ❌ Tried (didn't work) Initial app connection did not provide remote functions. Logging out and restarting the phone did not immediately solve it.
  ✅ What actually fixed it The issue appeared to be a combination of server-side authorization and vehicle state. After driving the vehicle, the PIDs updated, and after some time (and contact with Lincoln support), the remote functions began to work. This highlights that the fix is not always instantaneous after installation.
• CyanLabs Forum User (2017 Lincoln MKZ Hybrid) — Installed a newer 4G TCU (KS7T-14G229-AH) to replace the original 3G unit. The app showed vehicle location but all other functions were blank.
  ❌ Tried (didn't work) Simply installing the newer TCU did not work as it was not compatible with the vehicle's older platform configuration out of the box.
  ✅ What actually fixed it The newer 'K' series TCU required a firmware *downgrade* using FORScan to be compatible with the 2017 vehicle. The As-Built data also had to be modified to match the vehicle's original configuration. This is a critical warning that a 'newer' part isn't always a direct swap.
• CyanLabs Forum User (2021 Ford Transit (similar SYNC/TCU architecture)) — Lost FordPass communication (U0198:87) after an aftermarket 4-inch to 8-inch SYNC screen conversion.
  ❌ Tried (didn't work) Checking harness wiring, SYNC master reset, verifying HS4 CAN was enabled in the APIM.
  ✅ What actually fixed it The TCU was not accessible initially. After driving, the TCU became visible in FORScan. The final fix was changing a single line of As-Built data in the TCU module: address 754-18-01 was changed to '0304', which restored the connection.

OEM Part Supersession History

• G-series (e.g., GP5T-14G087-DF) → H, J, or K-series (e.g., HJ5T-14G229, JL3T-14G229) — Upgrade from 3G cellular technology to 4G/LTE. The 3G network was shut down in 2022, rendering all G-series modems obsolete.
  Heads up: When upgrading, you cannot simply install any 4G modem. The firmware and As-Built data must be programmed for the specific vehicle platform. For example, one expert noted that using a TCU from a 2020 model in a 2017/2018 caused intermittent 'failure to wakeup' issues, and recommended using a 2019-sourced As-Built file instead.

Model Year Variations Within This Range

• 2015-2017: These years were factory-equipped with 3G TCUs. Due to the 2022 cellular network shutdown, a U0198 code on these models is almost certainly due to the obsolete modem, requiring a hardware upgrade to a 4G unit.
• 2018-2019: These years came from the factory with 4G TCUs. A U0198 code is more likely to be a software glitch (requiring a fuse pull), a failed module, or a wiring issue, rather than network obsolescence.