U0158 on 2020-2023 Cadillac CT4: Head-Up Display Communication Loss Fixes

What's Unique About the 2020-2023 Cadillac CT4

For this specific generation of Cadillac CT4 and its platform-mate, the CT5, the U0158 code is strongly associated with a known software issue acknowledged by General Motors. A Technical Service Bulletin (TSB #22-NA-113) was issued because the timing of data messages on the vehicle's LIN bus can cause the HUD to get stuck in standby mode. 🎬 Watch: How the Cadillac HUD system is designed to operate. Unlike a generic communication code that might point to wiring or module failure, on these cars, the root cause is very frequently a software problem that requires a specific update from the dealer. The TSB explicitly states the fix is to reprogram the IPC and then perform a hard reset of the HUD by pulling its fuse.

Diagnostic Flowchart

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

Symptoms You May Notice

• Head-Up Display (HUD) is blank or completely inoperative.
• HUD does not respond to brightness, position (aim), or page control adjustments.
• The HUD may start working again after turning the car off, opening the driver's door, and then restarting the car.
• Intermittent flicker or garbled/distorted graphics may appear before the display goes completely blank.

Most Likely Causes

1. Instrument Panel Cluster (IPC) Software Glitch 🔴 High Probability As documented in TSB #22-NA-113, a data timing issue on the LIN bus can cause the HUD to get stuck in standby mode. This is a known firmware problem specific to these models.
   How to confirm: A GM dealer can check the vehicle's software calibration history against the latest version specified in TSB #22-NA-113. The presence of U0158 as a current or history code is the primary indicator.
   Typical fix: Reprogram the Instrument Panel Cluster (IPC) with updated software. After reprogramming, the TSB specifies that the technician must remove the HUD fuse for at least 10 minutes to reset the module, then reinstall it to verify the fix.
   Est. part cost: $0
2. Power Supply or Fuse Issue 🟡 Medium Probability
   How to confirm: Check the fuse for the Head-Up Display. On the CT4, this is located in the instrument panel fuse block, which is at the end of the driver's side of the dashboard, accessible when the door is open. Test for 12V power and a solid ground at the HUD module connector.
   Typical fix: Replace the blown fuse. If the fuse is good, diagnose the power or ground circuit for faults. A simple fuse pull for 30 seconds can sometimes temporarily reset the module.
   Est. part cost: $1-$5
3. Faulty Head-Up Display Module ⚪ Low Probability
   How to confirm: If the IPC software is up to date per TSB #22-NA-113 and all wiring, power, and grounds are confirmed good, the HUD module itself is the likely point of failure. The TSB explicitly states that if the HUD is still not functional after the software fix and fuse reset, the bulletin no longer applies and standard diagnostics should be followed.
   Typical fix: Replace the Head-Up Display unit. This requires significant dashboard disassembly and the new module may need programming to the vehicle.
   Est. part cost: $400-$800

Rare But Worth Checking

• Wiring Harness or Connector Damage: While not common for this specific code on this platform, a loose connector or damaged wire on the LIN bus between the Instrument Panel Cluster and the HUD can interrupt communication and set this code. This should be checked before replacing expensive modules, especially if the software update fails to resolve the issue.

Diagnosis Steps

1. Check for Technical Service Bulletins (TSBs). TSB #22-NA-113 is the primary document for this issue on the CT4 and CT5.
2. Verify the symptoms. Confirm the HUD is blank and unresponsive to controls.
3. Attempt a simple reset. Turn the vehicle off, open and close the driver's door, and wait a few moments before restarting the engine to see if the HUD resumes function. This is a temporary fix reported by owners.
4. Check the HUD fuse. Locate the instrument panel fuse block on the driver's side of the dash and inspect the fuse for the HUD. If blown, replace it. If not, a 30-second pull might temporarily restore function.
5. Visit a dealer for software update. If simple resets fail, the definitive next step is to have a GM dealer reprogram the Instrument Panel Cluster (IPC) as per TSB #22-NA-113.
6. Verify the TSB repair procedure. Ensure the dealer follows the TSB by not only reprogramming the IPC but also removing the HUD fuse for 10 minutes to complete the reset.
7. Inspect wiring. If the software update does not resolve the issue, inspect the wiring harness and connectors between the IPC and the HUD for any visible damage or loose connections.
8. Test power and ground. Using a multimeter, check for proper voltage and ground at the HUD module's electrical connector.
9. Diagnose the HUD module. If all previous steps fail, the HUD module itself is likely faulty and requires replacement.

Parts You'll Likely Need

• Head-Up Display Unit (OEM #84899768) — This is replaced only if the software update and wiring checks fail to solve the problem. It is the hardware that projects the image. Part number 84899768 supersedes 84695799 and 84840604.
  Trusted brands: ACDelco, GM Genuine Parts
  OEM price range: $480-$700
  Aftermarket price range: $400-$600

Technical Service Bulletins (TSBs) & Recalls

• 22-NA-113: Addresses a blank or unresponsive Head-Up Display (HUD) with DTC U0158 set, caused by a software timing issue on the LIN bus. The fix is to reprogram the Instrument Panel Cluster (IPC) and then reset the HUD by removing its fuse for 10 minutes. This TSB applies to both the Cadillac CT4 and CT5.

Platform-Specific Known Issues

• A known software issue covered by TSB #22-NA-113 can cause the HUD to become unresponsive due to data timing errors on the LIN bus, setting code U0158.
• This issue is shared with the 2020-2023 Cadillac CT5, which is built on the same GM Alpha 2 platform.

Mechanic-Grade Diagnostic Values

• LIN Bus Voltage (at HUD connector, key on) — expected: A toggling voltage that ranges between approximately 1V and 1V less than battery system voltage (e.g., ~11.5V). When at rest, the voltage should be steady at approximately battery system voltage.. Failure: Voltage that is stuck high (at battery voltage), stuck low (near 0V), or does not toggle indicates a communication failure, short, or open circuit.
• Power Supply Voltage at HUD Module Connector — expected: 12.0 V ± 0.5 V with ignition on.. Failure: Voltage below the minimum threshold can cause the module to shut down and log a communication fault.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Module Diagnostics > Instrument Panel Cluster > Data Display — To monitor the status and data parameters being sent from the IPC to the HUD. This helps confirm if the master module (IPC) is attempting to communicate.
• GDS2 (GM Global Diagnostic System 2): Module Diagnostics > K43 Head-Up Display Control Module > Data Display / Control Functions — If communication can be established, this allows a technician to view the HUD module's status and perform bidirectional controls (e.g., command display on/off, change brightness) to test its functionality directly, bypassing the physical switches. Inability to access this module points directly to the communication failure.
• SPS (Service Programming System): Instrument Panel Cluster (IPC) - Programming — This is the function required to perform the software update as specified in TSB 22-NA-113. A stable power supply is critical during this procedure.

Wiring & Ground Locations

• K43 Head-Up Display Control Module Connector — Located at the Head-Up Display unit itself, which is installed in the top of the instrument panel, near the base of the windshield.. This is the primary connection point for testing power, ground, and the LIN Bus signal directly at the module. A wiring diagram is needed to identify the specific pins.
• LIN Bus Circuit — A single wire running from the Instrument Panel Cluster (IPC) to the K43 Head-Up Display Control Module.. This single wire is the communication line. Any damage, short to ground, or short to power along its path will cause code U0158. Technicians can test for a valid signal on this wire at either the IPC connector or the HUD connector.

Real Owner Repair Stories

• Cadillac V-Series Forums (2022 CT4) — Head-Up Display didn't come on at all.
  ❌ Tried (didn't work) The user did not report trying other fixes.
  ✅ What actually fixed it Stopping the car, turning it off, opening the driver's door, and then restarting the car temporarily resolved the issue, which is consistent with the software glitch described in TSB 22-NA-113 that can be reset by a power cycle.