U0158 on 2020-2023 Cadillac CT5 & CT4: Head-Up Display Communication Loss Fixes

What's Unique About the 2020-2023 Cadillac CT5

For the 2020-2023 Cadillac CT5 and its platform-mate, the CT4, this specific code is frequently caused by a software timing issue within GM's Vehicle Intelligence Platform (VIP) electrical architecture. GM identified that certain data messages can cause the HUD to get stuck in standby mode when the ignition is cycled. Unlike a hard-part failure, the issue is often resolved by a specific software update for the Instrument Panel Cluster (IPC), making a trip to the dealer for reprogramming the most direct and cost-effective solution.

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, aim, or page control adjustments via the steering wheel or dashboard buttons.
• The HUD may work correctly on one ignition cycle and fail on the next, seemingly at random.
• The Check Engine Light is typically NOT illuminated by this code, though a message may appear in the Driver Information Center (DIC).
• When trying to adjust HUD settings, the menu may be grayed out or unresponsive.

Most Likely Causes

1. Instrument Panel Cluster (IPC) Software Anomaly 🔴 High Probability A known issue documented in TSB #22-NA-113 describes a data timing problem on the LIN bus that causes the HUD to get stuck in standby mode during ignition cycles. This is a well-documented firmware issue specific to the GM VIP architecture on these models.
   How to confirm: A GM dealer technician can verify if the software update from TSB #22-NA-113 has been applied to the vehicle using the Techline Connect system by checking the vehicle's service history and the IPC's current calibration ID.
   Typical fix: Reprogram the Instrument Panel Cluster (IPC) with the latest software version available in SPS2. After the reprogram, the bulletin specifies performing a hard reset of the HUD by removing its fuse for at least 30 seconds (some cases may require up to 10 minutes).
   Est. part cost: $0
2. Faulty Head-Up Display (HUD) Unit ⚪ Low Probability While less common, the HUD projector unit contains its own electronics that can fail. This is typically only considered after the TSB software update has been performed and has failed to resolve the issue.
   How to confirm: If the IPC software is up to date and the HUD still does not communicate, the module itself is suspect. A technician can use a GDS2 scan tool to attempt direct communication with the HUD. If it's unresponsive and power, ground, and LIN bus signal are verified as good at the HUD connector, the unit has likely failed internally.
   Typical fix: Replace the entire Head-Up Display projector unit. This is a labor-intensive job that requires significant dashboard disassembly.
   Est. part cost: $800-$1500
3. Wiring or Connector Issue ⚪ Low Probability While not a pattern failure, any vehicle can experience wiring issues. The LIN bus wire between the IPC and HUD is a single point of failure. Connectors can become loose or corroded, though this is rare on newer vehicles.
   How to confirm: Visually inspect the wiring harness and connector at the back of the HUD unit for damage or looseness. Using a multimeter or oscilloscope, check for stable battery voltage, a clean ground, and a valid LIN bus signal 🎬 Watch: A practical guide to diagnosing LIN bus communication issues. (typically a fluctuating voltage signal) at the HUD connector.
   Typical fix: Repair the damaged section of the wiring harness or clean/re-seat the connector. Applying dielectric grease can prevent future corrosion.
   Est. part cost: $10-$100

Rare But Worth Checking

• Blown HUD Fuse:

Diagnosis Steps

1. Connect a GM-specific scan tool (like GDS2) to the OBD-II port to confirm U0158 is the primary code stored in the Instrument Panel Cluster (K20).
2. Check for any applicable Technical Service Bulletins (TSBs) in the GM service information system. For this specific issue, TSB #22-NA-113 is the key document.
3. If TSB #22-NA-113 applies and has not been performed, schedule an appointment with a dealership to reprogram the Instrument Panel Cluster (IPC) to the latest software version using SPS2.
4. Following the reprogram, perform a hard reset of the HUD. With the ignition OFF, locate the HUD fuse in the driver-side instrument panel fuse block. Remove the fuse for at least 30 seconds, then reinstall it.
5. Turn the ignition on and verify if the HUD is now operational. If it is, the repair is complete.
6. If the HUD remains inoperative after the TSB procedure, proceed with standard electrical diagnosis. Backprobe the HUD electrical connector to check for stable battery voltage and a clean ground using a multimeter.
7. Inspect the LIN bus wiring between the IPC and the HUD for any signs of chafing, breaks, or corrosion. The LIN signal can be checked with an oscilloscope for proper data transmission. A healthy signal fluctuates between ~1V and ~12V.
8. If all wiring, power, and ground are confirmed good, and the IPC software is up-to-date, the Head-Up Display unit itself is the most likely point of failure and requires replacement.

Parts You'll Likely Need

• Head-Up Display Unit (OEM #85163349 (supersedes 84695209, 84898749)) — This part is only needed if the TSB software update and wiring checks do not resolve the issue, indicating an internal failure of the HUD projector or its integrated control module. Part number may vary by specific vehicle options.
  Trusted brands: ACDelco (GM Genuine)
  OEM price range: $900-$1500
  Aftermarket price range: N/A

Technical Service Bulletins (TSBs) & Recalls

• 22-NA-113: Head Up Display (HUD) Blank, Non-Responsive to Brightness, Aim, or Page Controls, DTC U0158 Set. This TSB provides the definitive diagnostic path, pointing to an IPC software reprogram and subsequent HUD fuse pull to resolve the condition. It explicitly states the cause is a LIN bus data timing issue.
• 21-NA-127: An earlier bulletin that suggested only a fuse pull for a similar condition (DTC U1518), which was later superseded by the more comprehensive software fix in 22-NA-113.

Platform-Specific Known Issues

• A software timing issue is a well-documented cause for this code on 2020-2023 CT5 and CT4 models, addressed by TSB #22-NA-113.
• Owner forums confirm that an ignition cycle can sometimes temporarily resolve the blank HUD, which is consistent with the 'stuck in standby' cause described in the TSB.

Mechanic-Grade Diagnostic Values

• LIN Bus Voltage (at HUD connector, measured with an oscilloscope 🎬 See this expert case study on advanced LIN bus troubleshooting. or a multimeter on Peak Min/Max) — expected: Signal fluctuating between a minimum of ~1.0V and a maximum of ~12.0V (or 1V below battery system voltage).. Failure: A steady, non-fluctuating voltage of approximately 12V indicates the bus is at rest or there is no communication from the master module (IPC). A constant 0V indicates a short to ground.

Scan Tool Commands That Help

• GM GDS2 (Global Diagnostic System 2): Module Control Functions / Bi-Directional Controls — After confirming the U0158 code, a technician can use GDS2 to manually command the Instrument Panel Cluster (the master module) to activate the HUD. If the HUD responds to a direct command but not during normal operation, it strongly suggests a software or intermittent communication issue rather than a hard failure of the HUD unit itself.

Wiring & Ground Locations

• LIN Bus Circuit — The single wire running between the Instrument Panel Cluster (IPC) connector and the Head-Up Display (K73) module connector.. The HUD communicates exclusively over this single LIN bus wire. Unlike CAN bus with high and low lines, this single wire is the only data path. A break, short, or high resistance on this specific wire will directly cause a U0158 code. Diagnosis involves checking signal integrity at the HUD connector end.

Real Owner Repair Stories

• Cadillac V-Series Forums (Cadillac CT4 (platform-mate to the CT5)) — Head-Up Display did not come on at all after starting the car.
  ❌ Tried (didn't work) Pressing the HUD control buttons on the dash.
  ✅ What actually fixed it Temporarily fixed by stopping the car, turning it off, opening the driver's door (to ensure modules fully power down), and then restarting the vehicle. This forced a complete power cycle of the modules and restored HUD function for that trip.