U0073 on a 2010-2016 Buick LaCrosse: Control Module Communication Bus 'A' Off Guide

What's Unique About the 2010-2016 Buick LaCrosse

The second-generation Buick LaCrosse (2010-2016) is built on the GM Epsilon II platform and integrates dozens of electronic modules highly dependent on the GMLAN for normal operation. A unique aspect of some GM platforms from this era is the location of certain modules, like the Transmission Control Module (TCM), which is housed inside the transmission as part of the TEHCM (Transmission Electro-Hydraulic Control Module). A failure of this internal module is a known issue and can cause network codes. GM vehicles of this period are also notoriously sensitive to low battery voltage, which can easily trigger network-wide communication faults like U0073 during startup. Furthermore, issues like clogged sunroof drains can lead to water intrusion in the cabin, directly causing corrosion on network wiring and connectors in the kick panels or under the seats.

Symptoms You May Notice

• Check Engine Light is on
• ABS, Traction Control, and Stabilitrak warning lights are on
• Service Power Steering message may appear
• Transmission may not shift correctly or may be stuck in one gear (Limp Mode)
• Vehicle may not start, or may crank but not start.
• Loss of power features like windows, door locks, or interior lights.
• Erratic or unresponsive instrument cluster gauges; speedometer may drop to zero
• Multiple 'Lost Communication' codes (U0100, U0101, U0121, U0140) stored alongside U0073.

Most Likely Causes

1. Weak or Failing Battery 🔴 High Probability → Shop Vehicle Battery Modern GM vehicles have a high electrical demand, and low system voltage (below 12.4V) during startup or operation can cause control modules to fail to initialize properly, leading to network communication errors.
   How to confirm: Test the battery voltage with a multimeter. A healthy battery should have at least 12.4V with the engine off and show 13.7V-14.7V with the engine running. A simple voltage test is not enough; perform a load test to check its true health.
   Typical fix: Charge or replace the battery. Ensure battery terminals are clean and tight. In many forum cases, this is the first and easiest fix to attempt.
   Est. part cost: $150-$300
2. Damaged or Corroded CAN Bus Wiring/Connectors 🟡 Medium Probability Wiring harnesses can become chafed from vibration, damaged by rodents, or suffer from corrosion due to water intrusion. On the LaCrosse, clogged sunroof drains are a known cause of water leaking into the cabin. Additionally, NHTSA ODI #11093337 regarding a similar Buick model noted a U0073 code where leaks from the air conditioner were suspected of affecting the sensors.
   How to confirm: Visually inspect the main wiring harnesses for any signs of damage, pinching, or green/white corrosion in connectors. Pay close attention to the area around the OBD-II port, BCM (often behind the glovebox or in the center console), and under the driver's side dash. A professional would test the CAN bus resistance (should be ~60 ohms between Pin 6 and Pin 14 of the DLC with battery disconnected) and use an oscilloscope to check for a clean signal.
   Typical fix: Repair the damaged section of the wire or replace the corroded connector. This requires precision and proper sealing to prevent future issues.
   Est. part cost: $5-$100
3. Faulty Control Module 🟡 Medium Probability Any single module on the network (e.g., EBCM/ABS, BCM, TCM) can fail internally and 'shout' on the network, bringing all communication to a halt. On GM vehicles, the ABS module (EBCM) and Body Control Module (BCM) are common points of failure that can cause this code.
   How to confirm: This requires a professional scan tool to see which modules are not responding. The diagnostic process involves unplugging modules one by one (starting with the most likely culprits like ABS and BCM) to see if communication is restored to the others. The module that allows the network to come back online when disconnected is the faulty one.
   Typical fix: Replace the failed module. The new module will require programming by a dealer or a qualified shop with the correct GM software (SPS).
   Est. part cost: $200-$1000+
4. Poor Ground Connections ⚪ Low Probability Ground straps and connection points (G-points) can corrode or become loose over time, creating an unstable electrical environment for control modules, which can lead to communication issues.
   How to confirm: Inspect, clean, and tighten major ground points for the engine, body, and battery. Key grounds are often located on the engine block, frame rail near the battery, and under the dash near the A-pillars.
   Typical fix: Clean the ground point to bare metal and secure the connection with a star washer and dielectric grease.
   Est. part cost: $0-$5

Rare But Worth Checking

• Aftermarket Electronics: Improperly installed remote starters, alarms, or audio equipment can interfere with or short the CAN bus network, causing communication errors. If the problem started after an installation, this should be the first thing you disconnect.

Diagnosis Steps

1. Check the battery voltage and charging system output. Ensure the battery is fully charged (12.4V+) and terminals are clean. A weak battery is a primary cause.
2. Perform a full vehicle scan with a high-end scan tool capable of communicating with all modules. Note which modules are not responding. A flood of 'U' codes is expected.
3. Visually inspect major wiring harnesses, especially around the OBD-II port, under-dash fuse box, BCM, and engine bay for any signs of damage, corrosion, or aftermarket splices. Check for signs of water intrusion in the cabin footwells.
4. Disconnect the battery. Measure the resistance between Pin 6 (CAN High) and Pin 14 (CAN Low) at the OBD-II port. A healthy network should read approximately 60 ohms. A reading of 120 ohms indicates an open circuit or a missing terminating resistor. A reading of 0 ohms indicates a short between the high and low lines.
5. If resistance is correct, the fault is likely a module. If resistance is incorrect, a wiring issue is likely.
6. Begin disconnecting individual modules one at a time, re-checking if communication is restored with the remaining modules. Common modules to start with are the ABS/EBCM and the BCM. The module that, when disconnected, allows the network to function is the likely culprit.
7. If a faulty module is identified, replace it. Note that many modules (like the BCM, ECM, or EBCM) require programming to the vehicle's VIN using GM's Service Programming System (SPS).

Parts You'll Likely Need

• Body Control Module (BCM) (OEM #22860592 (Verify with VIN, part numbers vary by year and options)) — The BCM is a central hub for many vehicle functions and a common point of failure on GM vehicles that can bring down the entire CAN network. It often requires dealer programming.
  Trusted brands: ACDelco (Genuine GM)
  OEM price range: $250-$500
  Aftermarket price range: $150-$350
• ABS Control Module (EBCM) (OEM #20956291 (Verify with VIN, part numbers vary by year and options)) — A faulty ABS module is a very common cause of U0073 on this platform. It can fail internally and disrupt all network communication, often logging a U0121 code in other modules.
  Trusted brands: ACDelco, Bosch
  OEM price range: $400-$800
  Aftermarket price range: $200-$500 (often remanufactured)
• Battery (OEM #ACDelco Gold 48AGM (Group 48/H6 AGM)) — A weak or failing battery is a very common and simple cause for complex communication codes due to low system voltage. Always rule this out first.
  Trusted brands: ACDelco

Related Codes That Often Appear With This One

• U0100 — Lost Communication with ECM/PCM
• U0101 — Lost Communication with TCM
• U0121 — Lost Communication with Anti-Lock Brake System (ABS) Control Module - This is a very common companion code and points towards the ABS module or its wiring as a potential cause.
• U0140 — Lost Communication With Body Control Module

Technical Service Bulletins (TSBs) & Recalls

• While no TSB is a direct match for 'U0073 on Buick LaCrosse', GM TSB PIP4653E addresses various communication DTCs (including U-codes) in the TCM and advises confirming the code's origin before replacing parts, which is relevant to the diagnostic process for U0073.

Platform-Specific Known Issues

• Water intrusion from clogged sunroof drains is a known issue on the 2010-2016 LaCrosse. The water can leak down the A-pillars and into the kick panel area, corroding critical network connectors and ground points, which can directly cause a U0073 code.

Mechanic-Grade Diagnostic Values

• High-Speed GMLAN (CAN Bus) Resistance — expected: ~60 Ohms. Failure: A reading of ~120 Ohms indicates an open circuit or one of the two terminating resistors is offline. A reading near 0 Ohms indicates a short between the CAN High and CAN Low wires.
• CAN High Voltage to Ground — expected: ~2.6V (average with multimeter, network active). Failure: Significant deviation, 0V, or battery voltage indicates a fault. An oscilloscope shows switching between 2.5V and 3.5V.
• CAN Low Voltage to Ground — expected: ~2.4V (average with multimeter, network active). Failure: Significant deviation, 0V, or battery voltage indicates a fault. An oscilloscope shows switching between 2.5V and 1.5V.
• Resistance from CAN lines to Ground — expected: Megaohms or Open Circuit (OL). Failure: Low resistance or continuity indicates a short to ground on either the CAN High or CAN Low circuit.

Scan Tool Commands That Help

• GM GDS2 (Global Diagnostic System 2): Data Bus Diagnostic Tool — This is a guided routine within the GM service software that helps technicians diagnose network faults like U0073. It provides a list of all expected modules and shows which ones are not communicating, helping to isolate the source of the network failure.
• GM SPS (Service Programming System): BCM Body Control Module Programming / Setup — This function is mandatory after replacing the Body Control Module (BCM). It downloads the correct software and configuration for the vehicle's specific VIN and options. Failure to program a new BCM will result in a no-start condition and multiple system malfunctions.
• GM GDS2 / Tech2Win: Immobilizer Learn / Key Relearn — After replacing and programming a major control module like the BCM or ECM, the vehicle's anti-theft system must be re-synchronized with the keys. This procedure, sometimes called the '30-minute relearn', is required to allow the engine to start.

Wiring & Ground Locations

• OBD-II DLC Pins — Under the driver's side dashboard, to the left of the steering column.. Pin 6 (CAN High) and Pin 14 (CAN Low) are the primary test points for measuring network resistance and voltage.
• G302 / G303 — G302 is located near the rear fuse block, under the rear seat on the driver's side. G303 is located under the passenger seat and is a ground for the inflatable restraint module.. While from a different GM model, these interior ground locations (G3xx series) are typical for grounding cabin modules. A loose or corroded ground at one of these points can cause communication issues for modules like the SDM (Airbag) or BCM, potentially triggering a U0073.
• BCM Location — Typically located in the driver or passenger side kick panel area or behind the dash.. The BCM is a common failure point. Knowing its location is critical for visual inspection of its connectors for corrosion (especially from water leaks) and for disconnecting it as a diagnostic step.
• Bellhousing Grounds — On some GM engines, ground terminals for the main wiring harness attach to bolts on the transmission bellhousing.. These are critical engine-to-chassis grounds. If they are loose, corroded, or not reattached properly after service, it can cause unstable power for the ECM and TCM, leading to network codes.

Real Owner Repair Stories

• YouTube Channel 'ECU Team Corp' (2014 Buick LaCrosse) — Crank, no-start condition.
  ❌ Tried (didn't work) The customer replaced the Engine Control Module (ECM) themselves, but the car still would not start.
  ✅ What actually fixed it The root cause was a faulty starter relay that was not receiving power. After bypassing/adjusting the relay, the car started with both the original and the replacement ECM. The initial diagnosis of a bad ECM was incorrect; the actual problem was a simpler power delivery issue to the starter circuit.

OEM Part Supersession History

• 13580696 → 123589093, 13588446, 13584692, 13583542 — Standard part revisions and updates by the manufacturer.
  Heads up: These part numbers are listed as interchangeable for 2012-2013 models, but VIN verification is always critical. The key issue is not incompatibility between parts, but the need for programming to the specific vehicle.

Model Year Variations Within This Range

• 2014: The 2014 model year received a significant facelift with updated electronics, including a new 8-inch instrument cluster display and new driver assistance features like Lane Change Alert and Forward Collision Alert. This introduces different software and potentially different module part numbers compared to the 2010-2013 models.
• 2014 (early production): A recall (GM #14235) was issued for certain 2014 LaCrosse vehicles for a wiring splice in the driver's door that could corrode and break. While this recall specifically addressed issues with the door-open chime and Retained Accessory Power, any corrosion in a critical wiring harness is a potential source for network communication problems.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Premature Timing Chain Stretch (3.6L V6) 🔴 High — Common between 40,000 and 120,000 miles, particularly on earlier LLT engines (2010-2011). Often presents with codes P0008, P0009, P0017, etc. (Ref: TSB #12-06-01-009F details updated parts; Special Coverage Adjustment #11340 extended warranty (now expired for most).)
• TEHCM (TCM) Failure in 6T70/6T75 Transmission 🔴 High → Shop Transmission Assembly — The Transmission Electro-Hydraulic Control Module (TEHCM), located inside the transmission, is prone to failure from heat and vibration, causing harsh shifting, no-shift conditions, or complete failure. (Ref: Multiple TSBs exist for various shifting symptoms. A common related code is U1000 for loss of communication with the TCM.)
• Clogged Sunroof Drains Causing Water Leaks 🟠 Medium — The four sunroof drain tubes can become clogged with debris, causing water to overflow from the drain channel and leak into the cabin, often soaking the floorboards, A-pillars, or trunk. This can lead to mold and electrical problems.
• Throttle Body Assembly Failure 🟠 Medium — Can cause the vehicle to enter 'Reduced Engine Power' mode, with an unstable idle and poor acceleration. Often associated with code P2135.
• Faulty Wheel Speed Sensors / ABS Wire Breakage 🟡 Low — The wiring for the front wheel speed sensors can break internally from repeated flexing, causing ABS and Traction Control lights to illuminate.
• Corroded Rear Suspension Toe Links 🔴 High — Affects vehicles in heavy road salt regions. The protective coating fails, leading to corrosion and potential fracture of the toe link, causing a loss of vehicle control. (Ref: Recall #N212346640)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used BCM or EBCM can be a cost-effective option ONLY if you use a 'cloning' service. A used module taken directly from a salvage yard will not work because it is VIN-locked to the donor car. Cloning involves transferring all the data from your original faulty module to the used replacement, making it plug-and-play.

Donor-vehicle mileage cap: roughly under 120000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Ensure the part number exactly matches your original module or is a known compatible replacement.
• Inspect the connectors for any signs of corrosion, bent pins, or physical damage.
• Buy from a reputable seller who offers a warranty and confirms the module is from a vehicle that was not flood-damaged.
• If possible, obtain the VIN of the donor vehicle to cross-reference its options and history.

OEM-only on this vehicle (don't cheap out):

• Body Control Module (BCM)
• Engine Control Module (ECM)
• Transmission Control Module (TCM)
• Electronic Brake Control Module (EBCM)

Aftermarket brands forum-validated for this vehicle:

• ACDelco (Genuine GM / Remanufactured)

Brands owners have reported issues with on this vehicle:

• Unbranded, 'no-name' modules from online marketplaces without a warranty or clear programming instructions should be avoided. The complexity and programming requirements for these modules make quality and support essential.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• U0100 — Lost Communication with ECM/PCM; often stored alongside U0073 when the communication bus is disrupted.
• U0101 — Lost Communication with TCM; frequently appears with U0073 during network-wide failures.
• U0121 — Lost Communication with Anti-Lock Brake System (ABS) Control Module; a common companion code when the EBCM is the cause of the bus shutdown.
• U0140 — Lost Communication with Body Control Module (BCM); often seen when the BCM or its wiring is compromised.
• P0856 — Traction Control Input Signal; can be triggered as a secondary code when the ABS/EBCM module fails to communicate on the CAN bus.
• P0008 — Engine Position System Performance Bank 1; while not a communication code, it is a known issue on 2010-2011 3.6L LaCrosse models that may be present during a full vehicle scan.

Frequently Asked Questions