U0164 on 2017-2019 GMC Sierra 1500: HVAC Communication Loss Causes and Fixes

What's Unique About the 2017-2019 Gmc SIERRA 1500

What makes this issue unique on this generation of GMC Sierra is the high probability of the Serial Data Gateway Module (SDGM) being the root cause. GM has issued multiple Technical Service Bulletins (TSBs) about the SDGM entering a 'logic lock' state, where an error in the microcontroller causes it to power on but fail to communicate on any CAN channel. This takes other modules like the HVAC system offline with it. This is often accompanied by a host of other 'U' (communication) codes. The TSBs specifically point to this software glitch or poor terminal tension at the SDGM's X1 and X2 connectors.

Diagnostic Flowchart

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

Generation note: This range covers two Sierra 1500 generations: the K2XX platform (2017-2018 and 2019 'Limited' models) and the new T1XX platform (2019+). The primary documented cause, related to the Serial Data Gateway Module (SDGM), is a well-known issue on the K2XX platform per TSBs, but similar network architecture exists on the T1XX, making the diagnostic principles broadly applicable.

Symptoms You May Notice

• HVAC control panel is inoperative or completely dead.
• Cannot control fan speed, air temperature, or vent direction.
• Air conditioning will not turn on.
• Defroster is not working.
• HVAC pop-up display on the infotainment screen is blank or does not appear when controls are adjusted.
• If the SDGM is the cause, other symptoms may appear, such as instrument cluster gauges dropping to zero, multiple warning lights, a no-start condition, or the radio being inoperative.

Most Likely Causes

1. Serial Data Gateway Module (SDGM) Logic Lock or Connector Fault 🔴 High Probability This is a well-documented issue covered by GM Technical Service Bulletins #PIT5586G and #20-NA-212. The module's software can glitch ('logic lock'), or the X1 and X2 connector terminals can have poor contact or tension.
   How to confirm: Scan for other 'U' codes. If many are present, the SDGM is the prime suspect. Perform a hard reset by pulling the SDGM fuse (F26DL in the engine compartment fuse block) for 60 seconds. If HVAC controls return, even temporarily, a software 'logic lock' is confirmed.
   Typical fix: A GM dealer must reprogram the SDGM with updated software per TSB 20-NA-212. If the reset does not work, the X1 and X2 connectors at the SDGM must be inspected for bent or loose terminals and repaired as needed.
   Est. part cost: $0 (reprogram under warranty) - $450 (module replacement)
2. Blown Fuse 🟡 Medium Probability
   How to confirm: Check fuses related to the HVAC system (K33), Serial Data Gateway Module (SDGM), and Body Control Module (BCM). There are multiple fuse boxes: in the engine bay and on both sides of the instrument panel. Visually inspect the fuses or test for continuity with a multimeter.
   Typical fix: Replace the blown fuse. If it blows again, further diagnosis for a short circuit is needed.
   Est. part cost: $1-$5
3. Poor Ground Connection (G218) ⚪ Low Probability TSB #PIT5405C and #18-NA-161 identify a poor connection at ground G218 (under the driver's side dash near the A-pillar) as a cause for a wide range of electrical and communication issues on this platform.
   How to confirm: If multiple seemingly unrelated electrical issues are present along with U-codes, locate and inspect ground G218. Check for trapped insulation under the terminal or a loose connection.
   Typical fix: Clean the ground connection point to bare metal and securely tighten the ground bolt/nut.
   Est. part cost: $0-$5
4. Wiring or Connector Issue ⚪ Low Probability
   How to confirm: Visually inspect the wiring harnesses and connectors at the HVAC control module (behind the dash control panel) for any signs of damage, corrosion, or backed-out pins.
   Typical fix: Repair the damaged wire or clean/replace the affected connector.
   Est. part cost: $5-$50
5. Failed HVAC Control Module ⚪ Low Probability
   How to confirm: This should only be suspected if U0164 is the ONLY code present and all power, ground, and network tests at the module have passed. A professional scan tool can attempt to communicate directly with the module; a 'no response' confirms a failed module.
   Typical fix: Replace the HVAC control module. This may require programming to the vehicle.
   Est. part cost: $150-$400

Rare But Worth Checking

• Low Battery Voltage: A weak or failing battery can cause random communication codes as modules fail to initialize properly. Always ensure the battery is fully charged (12.4V+ with engine off) and the charging system is working before diagnosing network faults.

Diagnosis Steps

1. Scan for All DTCs: Use a quality OBD-II scanner that can read codes from all modules (BCM, IPC, Radio, etc.). Note if U0164 appears alone or with many other 'U' codes. A flood of U-codes points to the SDGM.
2. Check Battery Health: Verify the battery has a full charge (12.4V+ with engine off) and that the alternator is charging correctly (13.7-14.7V with engine running). Low voltage can cause communication faults.
3. Perform SDGM Reset (Logic Lock Test): Locate the fuse for the Serial Data Gateway Module (often F26DL in the underhood fuse block). Remove it, wait 60 seconds, and reinstall it. Check if HVAC function returns.
4. Evaluate Reset Results: If the reset temporarily fixed the problem, the SDGM has a 'logic lock' and requires a software update from a GM dealer per TSB 20-NA-212. If the reset did nothing, proceed to physical checks.
5. Inspect SDGM Connectors: If the reset failed, inspect the SDGM's X1 and X2 connectors for loose pins, corrosion, or damage, as directed by TSB PIT5586G. Repair any terminal issues found. A specific terminated lead (part #84619127) may be required for repair.
6. Inspect Fuses and Grounds: Check all fuses related to the HVAC system and Body Control Module (BCM). If multiple electrical issues are present, inspect ground G218 under the driver's side dash.
7. Test HVAC Module Power/Ground: If the SDGM and network seem okay, use a multimeter to verify the HVAC control module itself is receiving proper power and ground at its connector.
8. Final Module Diagnosis: If U0164 is the only code, the network seems stable, and the HVAC module has good power and ground, the module itself has likely failed and requires replacement.

Parts You'll Likely Need

• Serial Data Gateway Module (SDGM) (OEM #84524333 (Verify by VIN)) — This module is the most frequent cause of communication failures on this platform, often due to software glitches ('logic lock') or connector pin issues.
  Trusted brands: ACDelco (GM Genuine)
  OEM price range: $150-$250
  Aftermarket price range: $100-$200
• HVAC Control Module (OEM #84199202 or 84258726 (Varies by trim/options, verify by VIN)) — If all network tests pass and U0164 is the only code, the module itself may have failed internally.
  Trusted brands: ACDelco, Dorman
  OEM price range: $250-$400
  Aftermarket price range: $150-$300
• Terminated Lead Wire (OEM #84619127) — If a terminal in the SDGM's X1 or X2 connector is found to be damaged or has poor tension, this part is used to perform a professional repair per GM service procedures.
  Trusted brands: ACDelco (GM Genuine)
  OEM price range: $20-$40

Related Codes That Often Appear With This One

• U0100, U0101, U0140, U0155, U0184, etc. — When the Serial Data Gateway Module (SDGM) fails or locks up, it disrupts communication to multiple modules on the network, generating a flood of 'U' codes. Seeing many of these together strongly indicates the SDGM is the problem, as detailed in GM bulletin #PIT5586G.

Technical Service Bulletins (TSBs) & Recalls

• PIT5586G: Addresses multiple communication DTCs, including U0164, caused by a logic lock or connector issue at the Serial Data Gateway Module. Instructs technicians to check connectors.
• 20-NA-212: Replaces earlier TSBs for 2018+ models and details symptoms like inoperative HVAC controls, tracing the cause to the SDGM and recommending reprogramming as the primary fix.
• PIT5405C / 18-NA-161: A related bulletin that identifies a poor ground at location G218 as a potential cause for widespread communication faults and 'U' codes on this platform.

Platform-Specific Known Issues

• GM Technical Service Bulletin PIT5586G specifically identifies the Serial Data Gateway Module (SDGM) as a potential cause for U0164 and a wide range of other communication codes due to a microcontroller 'logic lock' or physical terminal issues at the X1 and X2 connectors.
• GM TSB 20-NA-212 supersedes earlier bulletins for newer models and prioritizes reprogramming the SDGM with updated software as the first corrective action for these symptoms before parts replacement.
• Owner experiences frequently describe a scenario where the climate controls suddenly die, are temporarily restored by pulling the SDGM fuse, only for the problem to return, confirming a software 'logic lock' issue.

Mechanic-Grade Diagnostic Values

• CAN Bus Network Resistance — expected: ~60 Ω (Ohms) across CAN_H and CAN_L with battery disconnected.. Failure: A reading of ~120 Ω indicates an open circuit or a missing termination resistor. A reading of ~40 Ω or less may indicate a short or an extra termination resistor on the bus.
• High-Speed GMLAN Voltage (Key On, Engine Off) — expected: CAN_H: ~2.6V, CAN_L: ~2.4V. These are biased from a 2.5V common voltage.. Failure: Voltages that are identical can indicate a short between the two wires. 0V on both can indicate a short to ground.
• Low-Speed GMLAN Voltage (Key On, Engine Off) — expected: Single wire bus that toggles between ~0.2V (recessive, logic '1') and >4.0V (dominant, logic '0').. Failure: A stuck-high or stuck-low voltage indicates a short to power or ground, or a failed module driving the bus.
• HVAC Control Module Ground Resistance — expected: < 1.0 Ω to a clean chassis point.. Failure: Higher resistance indicates a poor ground connection (like G218), which can prevent the module from communicating correctly.

Hidden / Shadow Codes Worth Checking

• DTC with Symptom Byte (e.g., U0164 71): GM uses a two-digit hexadecimal 'symptom byte' to provide deeper diagnostic detail. For example, '71' can mean 'Invalid Data Received', pointing to the transmitting module (HVAC) as the source of the fault, not the module that stored the code. '00' is a generic 'No Subtype Information'. (see via Requires a dealer-level scan tool like the GM GDS2 (Global Diagnostic System 2) or a high-end professional scanner with equivalent capabilities.)

Scan Tool Commands That Help

• GM GDS2 (Global Diagnostic System 2): Module Diagnostics > SDGM > Reprogramming — This is the primary fix when a 'logic lock' is confirmed by a temporary fix after a fuse pull. It uses the Service Programming System (SPS) to flash updated software to the module, as per TSB 20-NA-212.
• GM GDS2 (Global Diagnostic System 2): Module Diagnostics > HVAC Control Module > Control Functions — To perform bidirectional tests. A technician can command the HVAC module to change fan speed, blend doors, etc. If the module does not respond to direct commands but the network wiring tests good, it strongly suggests an internal module failure.
• GM GDS2 (Global Diagnostic System 2): Vehicle DTC Information > Display DTCs — To view the full list of codes from ALL modules on the vehicle. Seeing a flood of U-codes from many different modules is a key indicator that a gateway module (the SDGM) is the root cause, not the individual modules.

Wiring & Ground Locations

• SDGM (Serial Data Gateway Module) — Located under the driver's side dashboard, typically high up in the footwell area, often described as being about the size of a hockey puck with two connectors (one gray, one black).. This module is the central hub for network communication. TSBs point directly to it for logic locks and connector pin tension issues (X1 and X2) as the primary cause of U0164 and other U-codes.
• G218 — Under the driver's side dash, near the A-pillar, behind the plastic kick panel. It is a ground stud on the body.. This is a major ground point for multiple modules, including the BCM. TSB PIT5405C identifies that insulation can get trapped under the ground nut, causing high resistance and a wide array of seemingly unrelated electrical and communication faults.
• K33 (HVAC Control Module) — Located in the center of the dashboard, directly behind the physical climate control knobs and buttons.. This is the module that has lost communication. Technicians need to access its connector to test for power, ground, and network signals as a final step before condemning the module.

Real Owner Repair Stories

• gm-trucks.com forum user (2017 GMC Sierra) — HVAC controls completely dead, radio screen blank, multiple communication codes including U0164.
  ❌ Tried (didn't work) Checking all related fuses., Disconnecting the battery for a hard reset.
  ✅ What actually fixed it The user found TSB PIT5586G and performed the recommended 'fuse pull' reset for the SDGM. This temporarily restored all functions. The final fix was having the dealer reprogram the SDGM with the updated software specified in the bulletin. The problem did not return after the reprogram.

OEM Part Supersession History

• 13599318 → 13514248, 84524333 (and others, always verify by VIN) — Part revisions to address hardware or software vulnerabilities. Later part numbers are generally more reliable.
  Heads up: While physically interchangeable, a module from a different model year or vehicle line may not program correctly. It is critical to use a part number specified for the vehicle's VIN and have it programmed by a dealer.

Model Year Variations Within This Range

• 2019: The 2019 model year was a transition year. '2019 Sierra 1500 Limited' models are the older K2XX platform and are prone to the SDGM issues described. The 'new body style' 2019 Sierra 1500 is the T1XX platform, which has a different network architecture and does not use the same SDGM, making the specific TSBs less applicable.