U0073 on 2007-2010 Saturn Outlook: Causes and Fixes for Control Module Communication Failure

What's Unique About the 2007-2010 Saturn Outlook

The Saturn Outlook and its GM Lambda siblings (GMC Acadia, Buick Enclave, Chevy Traverse) are known for communication issues that can trigger a U0073 code. 🎬 Watch: Understanding the U0073 communication bus code and its causes. A GM Technical Service Bulletin (TSB PIT4730B) specifically addresses this, noting that intermittent shorts on the GMLAN data circuits (circuits 2500 & 2501) can cause the Body Control Module (BCM) to go offline for an entire ignition cycle. This often leads to the incorrect diagnosis of a failed BCM when the actual fault is in the wiring. The problem frequently occurs when driving over bumps or in wet conditions, pointing strongly to a physical wiring issue, often caused by water intrusion corroding wires in the driver's footwell area.

Symptoms You May Notice

• Check Engine Light is on
• Warning messages like "Service StabiliTrak," "Service Traction Control," or "Service Airbag" appear
• ABS and Traction Control lights are illuminated
• Engine may run in a reduced power mode ('limp mode').
• Transmission may shift harshly, get stuck in one gear, or not at all.
• Instrument cluster gauges behave erratically, go dead, or show dashes instead of readings.
• Vehicle may not start or may stall while driving
• Loss of features controlled by the BCM, like power locks, windows, or interior lights.
🎬 Watch: Common symptoms that indicate a failing Body Control Module.

Most Likely Causes

1. Intermittent Short/Open in CAN Bus Wiring due to Corrosion or Chafing 🔴 High Probability The Lambda platform is susceptible to water leaks from clogged sunroof drains, faulty windshield seals, or missing grommets. 🎬 See how water leaks commonly damage GM SUV wiring harnesses. This water pools in the driver's footwell, corroding the CAN bus wires that run in a harness under the door sill plate and in the driver's kick panel. Chafing is also common near the emergency brake pedal mechanism and where the harness passes through the firewall.
   How to confirm: Perform a thorough visual inspection of the harness in the driver's footwell. Peel back the carpet and remove the driver's door sill plate and kick panel. Look for signs of water staining, corrosion (often turning wires green), or damaged insulation on the twisted pair of CAN wires (Tan and Tan/Black). An advanced diagnostic step is to use a scan tool to monitor the network while performing a "wiggle test" on the harness.
   Typical fix: Repair the damaged section of wire. This involves cutting out the corroded or chafed portion, soldering in a new piece of wire (of the same gauge), and protecting the repair with adhesive-lined heat-shrink tubing to prevent future moisture intrusion.
   Est. part cost: $5-$20
2. Weak or Failing Battery / Poor Power Connections 🟡 Medium Probability → Shop Vehicle Battery All modern vehicles are highly sensitive to voltage. A weak battery can cause modules to fail to initialize correctly during startup, leading to network communication codes.
   How to confirm: Test the battery voltage with a multimeter. A healthy battery should read approximately 12.6 volts with the engine off and 13.7 to 14.7 volts with the engine running. Also, inspect the battery terminals and main ground straps (to the chassis and engine block) for cleanliness and tightness.
   Typical fix: Charge or replace the battery. Clean or replace corroded battery terminals and ground straps.
   Est. part cost: $150-$300
3. Failed Terminating Resistor (Internal to a Module) ⚪ Low Probability The high-speed GMLAN bus has two 120-ohm terminating resistors, typically located in the ECM and the EBCM (ABS module). If one of these modules fails internally, it can take the resistor offline and bring down the entire network.
   How to confirm: Disconnect the negative battery terminal. Using a multimeter, measure the resistance between Pin 6 (CAN High) and Pin 14 (CAN Low) at the OBD-II port. A healthy network will read approximately 60 Ohms. A reading of 120 Ohms indicates an open circuit or that one of the terminating resistors is not seen by the network. A reading near 0 Ohms indicates a short between the two CAN lines.
   Typical fix: If the resistance reading is 120 Ohms, further diagnosis is needed to isolate whether the fault is in the wiring or one of the terminating modules (ECM or EBCM). This involves disconnecting each module to see which one restores the proper resistance reading. The faulty module must be replaced.
   Est. part cost: $300-$1000+

Rare But Worth Checking

• Faulty Body Control Module (BCM): → Shop Body Control Module While possible, TSB PIT4730B specifically warns that a wiring issue can make a good BCM appear faulty. This should only be considered after all wiring and power supply issues have been exhaustively ruled out. Water intrusion is a known cause of BCM failure on these vehicles.
• Interference from Aftermarket Electronics: Improperly installed remote starters, alarms, or stereos can interfere with the CAN bus network by tapping into the wrong wires or creating electrical noise. If you have recently installed any aftermarket electronics, try disconnecting them to see if the problem resolves.

Diagnosis Steps

1. Check Battery and Charging System: Ensure the battery has a full charge (12.6V+) and that the alternator is charging correctly (13.7-14.7V). Clean any corrosion from the battery terminals and check that the main ground connections to the chassis and engine are secure.
2. Check for Water Intrusion: Pull back the driver's side carpet and inspect for dampness or signs of old water stains. Check sunroof drains to ensure they are not clogged.
3. Scan for All Codes: Use a professional scan tool to read codes from all modules. Note which modules are not communicating. This can provide clues to the location of the fault.
4. Check CAN Bus Resistance: Disconnect the negative battery terminal. At the OBD-II port, measure the resistance between Pin 6 (CAN High) and Pin 14 (CAN Low). A reading of ~60 Ohms is normal. A reading of ~120 Ohms indicates an open in the circuit or a problem with a terminating module. A reading near 0 Ohms suggests a short circuit.
5. Visual Inspection of Wiring: This is the most critical step for this vehicle. Remove the driver's door sill plate and kick panel. Carefully inspect the wiring harness for signs of chafing, melting, or green/white corrosion, especially the twisted pair of CAN wires. Pay close attention to the area near the BCM, the emergency brake pedal, and where the harness runs in the channel under the door.
6. Isolate the Fault: If the resistance check is abnormal or a visual fault isn't found, the next step is to disconnect modules on the high-speed CAN bus one by one (starting with the easiest to access) and re-checking resistance to see which one restores the correct reading. This is an advanced step and is best left to a professional.
7. Consult TSB PIT4730B: If the BCM appears to be offline, remember that it could be due to an intermittent wiring short. Do not replace the BCM until wiring has been proven to be intact.

Parts You'll Likely Need

• Battery — A weak or failing battery is a common cause of various electronic and communication faults in modern vehicles.
  Trusted brands: ACDelco
  OEM price range: $200-$300
  Aftermarket price range: $150-$250
• Body Control Module (BCM) (OEM #ACDelco 20941534, GM 13528941) — A potential, but less likely cause of the issue. It should only be replaced after exhaustive testing proves all wiring and other modules are functioning correctly. Water damage is a primary reason for failure on this platform. Requires programming upon installation.
  Trusted brands: ACDelco, Dorman
  OEM price range: $250-$400
  Aftermarket price range: $150-$250

Related Codes That Often Appear With This One

• U0100 — Lost Communication With Engine Control Module (ECM)
• U0101 — Lost Communication with Transmission Control Module (TCM)
• U0121 — Lost Communication With Anti-Lock Brake System (ABS) Control Module
• U0140 — Lost Communication With Body Control Module (BCM)

Technical Service Bulletins (TSBs) & Recalls

• PIT4730B

Platform-Specific Known Issues

• TSB PIT4730B highlights a known issue where intermittent shorts in the GMLAN wiring can cause the BCM to appear offline, leading to a U0073 code. This strongly suggests that any diagnosis should begin with a thorough inspection of the wiring harness before considering module replacement.

Mechanic-Grade Diagnostic Values

• High-Speed GMLAN Bus Resistance — expected: ~60 Ohms. Failure: A reading of ~120 Ohms indicates an open circuit or a missing terminating resistor. A reading near 0 Ohms indicates a short between the CAN High and CAN Low wires.
• High-Speed GMLAN Bus Voltage (Key On, Engine Off) — expected: CAN High (Pin 6 to ground): ~2.5V to 3.5V. CAN Low (Pin 14 to ground): ~2.5V to 1.5V.. Failure: Voltages stuck at 0V, 12V, or equal to each other indicate a short to ground, short to power, or short between the wires, respectively.
• BCM Power-Down Time — expected: Up to 20 minutes. Failure: N/A - This is an operational characteristic.

Hidden / Shadow Codes Worth Checking

• U0073 71: Control Module Communication Bus Off - Invalid Data. This specific symptom code is logged when the BCM intentionally shuts down communication due to detecting an intermittent short on the GMLAN bus. (see via A professional GM scan tool like a Tech2 or a modern tool with GDS2 software is required to see these symptom bytes.)
• U0073 72: Control Module Communication Bus Off - Alive Counter Incorrect. This indicates a communication timing or synchronization issue on the bus. (see via A professional GM scan tool is needed to view this symptom code.)

Scan Tool Commands That Help

• GDS2/Tech2: Setup SDM Primary Key in BCM — This function is required after replacing the Body Control Module (BCM). The new BCM must be synchronized with the Sensing and Diagnostic Module (SDM, i.e., the airbag module) to establish a secure link. Failure to do this will often result in an airbag warning light and stored DTCs in the SDM.
• GDS2/Tech2: Service Programming System (SPS) — This is the GM software suite used to flash/program a new or used BCM to the vehicle. It downloads the correct software and vehicle options based on the VIN. This is not a diagnostic command but a required programming step for module replacement.

Wiring & Ground Locations

• GMLAN Circuits 2500 & 2501 — These are the Tan/Black (2500, CAN Low) and Tan (2501, CAN High) twisted pair wires. They run in a major harness from the BCM under the driver's side dash, down through the driver's kick panel, and under the driver's door sill plate.. This is the primary location for water intrusion and corrosion, as well as chafing near the parking brake mechanism, as highlighted by TSB PIT4730B.
• G303 — Near the base of the left 'B' pillar (the pillar between the driver's door and the rear passenger door).. This is a major body ground point. While not directly for the BCM, a poor connection here can introduce electrical noise and voltage stability problems that affect multiple modules on the network.
• G301 — Located behind the left kick panel, near the BCM.. This is a critical ground point for several dash components. A loose or corroded G301 can cause intermittent issues with modules in that area.
• Splice Packs / Star Connectors — The GMLAN bus uses splice packs (also called star connectors) to branch the network to different modules. A key one is often located in the driver's side A-pillar area or behind the kick panel.. These connectors are a single point of failure. Corrosion inside a splice pack from water intrusion can take down the entire network or specific segments, causing a U0073.

Real Owner Repair Stories

• AcadiaForum.net user (2008 GMC Acadia (Lambda Platform sibling)) — Service Stabilitrak, Service Traction Control, engine power reduced, harsh shifting, multiple U-codes including U0073.
  ❌ Tried (didn't work) Replacing the throttle body, Replacing the accelerator pedal position (APP) sensor
  ✅ What actually fixed it The user found corroded wires in a harness located under the driver's side door sill plate. Water had leaked in and pooled in the channel, rotting the CAN bus wires. After cutting out the bad section and soldering in new wires, all communication was restored and the codes were cleared.

Diagnostic Flowchart

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used Body Control Module (BCM) from a junkyard can be a cost-effective option ONLY IF it comes from an identical vehicle (same year, model, and major options). However, it will almost certainly require professional reprogramming to your vehicle's VIN using GM's Service Programming System (SPS) to ensure all features work correctly and to avoid security system conflicts. For wiring harnesses, a used section from a donor vehicle is an excellent choice for repairing corroded or damaged sections.

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

What to inspect on the donor part:

• For a BCM: Ensure the donor vehicle was not involved in a flood or fire. Check the part number on the module to ensure it matches the original exactly.
• For a wiring harness section: Inspect for any signs of previous corrosion (green crust), melted insulation, or prior amateur repairs (tape, butt connectors). Ensure the wires are still flexible and not brittle.

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

• Body Control Module (BCM): While aftermarket BCMs exist (e.g., Dorman), they can sometimes have compatibility issues. For a critical component like this, a new OEM (ACDelco) part or a professionally remanufactured unit programmed to your VIN is the most reliable choice to avoid programming headaches.

Brands owners have reported issues with on this vehicle:

• Unbranded/no-name BCMs from online marketplaces should be avoided. They often cannot be programmed correctly or fail prematurely.

Real Owner Stories

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

Related OBD-II Codes

• U0140 — Lost Communication With Body Control Module. This is a very common companion code, as the wiring issue causing U0073 often directly affects the BCM's communication lines, as noted in TSB PIT4730B.
• U0121 — Lost Communication With Anti-Lock Brake System (ABS) Control Module. The ABS module (EBCM) is a critical terminating module on the high-speed CAN bus. A general network failure (U0073) will prevent communication with it, triggering this code and 'Service StabiliTrak' warnings.
• U0101 — Lost Communication with TCM (Transmission Control Module). A U0073 fault brings down the entire network, preventing the TCM from communicating. This often results in symptoms like harsh shifting or being stuck in one gear.
• U0100 — Lost Communication with ECM/PCM. The Engine Control Module (ECM) is one of the two terminating resistors for the network. A U0073 fault means the network is down, so communication with the ECM is inherently lost.
• P0856 — Traction Control Input Signal. This code is a direct result of the EBCM (ABS/Traction Control module) being offline due to the U0073 network communication failure. It is a symptom code, not a cause.

Frequently Asked Questions