U0073 on 2008-2012 Chevrolet Malibu: Causes and Fixes for Communication Bus Failure

What's Unique About the 2008-2012 Chevrolet Malibu

For the 7th generation Malibu and its platform mates (Pontiac G6, Saturn Aura), a U0073 code is frequently a symptom of another problem rather than a random wiring failure. A failing Transmission Control Module (TCM), located inside the transmission where it's exposed to heat and vibration, is a known weak point that can short out and bring the entire communication network down, often triggering a U0101 code (Lost Communication with TCM) at the same time. Additionally, these vehicles are highly sensitive to low voltage, and something as simple as a loose main battery ground cable has been documented by owners to cause this specific code.

Symptoms You May Notice

• Check Engine Light is on
• ABS, Traction Control, or StabiliTrak warning lights are on
• Engine may not start or may stall while driving
• Transmission shifts harshly, erratically, or gets stuck in 'limp mode'
• Instrument cluster gauges may drop to zero or behave erratically
• Loss of power steering assist
• Messages on the driver information center (DIC) like 'Service Engine Soon', 'Service StabiliTrak', 'Engine Power is Reduced'
• Car may not crank at all
• Doors may not lock/unlock with remote or power buttons

Most Likely Causes

1. Weak Battery or Poor Ground Connection 🔴 High Probability → Shop Vehicle Battery Modern control modules are highly sensitive to voltage. A loose main ground cable (a known issue discussed in forums), a failing battery, or corroded terminals can cause intermittent voltage drops that disrupt network communication.
   How to confirm: Test the battery voltage: it should be at least 12.4V with the engine off and 13.7V-14.7V while running. Physically inspect and tighten the main battery terminals and the primary body/engine ground straps. On the 3.6L V6, key ground points are on the engine block and strut towers. A loose ground can sometimes be seen creating a small spark when wiggled.
   Typical fix: Tighten loose connections or replace the battery if it fails a load test. Some owners add a redundant ground wire from the engine block to the chassis as a preventative measure.
   Est. part cost: $0-$250
2. Failing Transmission Control Module (TCM) 🟡 Medium Probability → Shop Transmission Assembly The TCM on this platform (part of the TEHCM unit) is located inside the transmission, where it is exposed to heat and potential fluid contamination, leading to a higher failure rate. A faulty TCM can short the communication bus internally.
   How to confirm: Scan all modules. If code U0101 (Lost Communication with TCM) is present along with U0073 and P0700, the TCM is the primary suspect. A professional can disconnect the TCM connector at the transmission case and see if communication with other modules is restored.
   Typical fix: The TCM, which is part of the valve body assembly, must be replaced. This requires removing the transmission side cover. 🎬 Watch: How to remove the Malibu transmission control module. The replacement module must be programmed with a GM scan tool (Tech 2 or MDI) to the vehicle's VIN.
   Est. part cost: $300-$700
3. Damaged or Corroded Wiring Harness 🟡 Medium Probability GM has issued service bulletins (e.g., #08-07-30-021H) for GMLAN communication loss on similar platforms due to the engine wiring harness chafing against the transmission case, firewall, or engine brackets. The main connector at the transmission is also a common point for fluid intrusion or corrosion.
   How to confirm: Visually inspect the wiring harness, especially where it runs near the transmission, firewall, and under-hood fuse block. Disconnect connectors at the TCM and BCM to check for green or white corrosion on the pins. Wiggle the harness while monitoring the bus with a scan tool to see if communication drops.
   Typical fix: Repair the damaged section of wire with solder and heat shrink, then protect the harness from further chafing using loom or by re-routing. Clean corroded connectors with an electrical contact cleaner.
   Est. part cost: $10-$100
4. Faulty Body Control Module (BCM) ⚪ Low Probability → Shop Body Control Module Any module on the network can fail and bring it down. However, GM service bulletin PIT4730B specifically warns that intermittent shorts on the CAN bus wires can make the BCM appear to be offline for an entire ignition cycle, leading to misdiagnosis. The fault often occurs over bumps.
   How to confirm: This requires a process of elimination. If the CAN bus resistance is incorrect, disconnect modules one by one (EBCM, PSCM, etc.) while monitoring the resistance to see which one is causing the fault. If the BCM is suspected, verify its power and ground connections are solid before condemning it.
   Typical fix: Replace the faulty module. The BCM requires programming to the vehicle's VIN and specific options after installation.
   Est. part cost: $250-$800

Rare But Worth Checking

• Blown Fuse: A fuse for a critical module like the ECM, TCM, or BCM could be blown. While not common, it's a simple check to perform in the under-hood and interior fuse panels before more complex diagnostics.
• Faulty Aftermarket Electronics: Improperly installed remote starters, alarms, or stereos can interfere with the CAN bus network by being spliced incorrectly into the data lines, causing communication errors.

Diagnosis Steps

1. Scan for Codes in All Modules: Use a high-quality scanner that can read codes from all modules (ECM, TCM, BCM, EBCM, etc.). Note all 'U' codes and which modules are not responding. The presence of U0101 is a major clue pointing to the TCM.
🎬 Watch: A simple fix for loss of TCM communication.
2. Check Battery and Grounds: Ensure the battery has a full charge (12.4V+). Start the engine and verify the alternator is charging (13.7-14.7V). Inspect and physically tighten the battery terminals and all major ground straps from the battery to the body and engine block. A loose ground is a common, simple fix.
🎬 See how to identify and fix common engine ground issues.
3. Check Fuses: Inspect fuses related to the ECM, TCM, and BCM in both the under-hood and interior fuse panels.
4. Check CAN Bus Resistance: Disconnect the negative battery terminal. At the Data Link Connector (DLC), use a multimeter to measure the resistance between Pin 6 (CAN High) and Pin 14 (CAN Low). A healthy network should read approximately 60 ohms.
5. Interpret Resistance Reading: If the reading is 120 ohms, there is an open in the circuit or one of the two terminating resistors (located in the ECM and BCM) is offline. If the reading is near 0 ohms, the CAN High and Low wires are shorted together.
6. Isolate the Fault: If resistance is incorrect, begin disconnecting modules from the CAN bus one at a time (starting with the TCM if U0101 is present) and re-measure resistance. When the resistance returns to 60 ohms, the last module disconnected (or its wiring/connector) is the source of the problem.
7. Visual Wiring Inspection: Thoroughly inspect the harness for chafing, melting, or corrosion, paying close attention to the area around the transmission, near the underhood fuse block, and where the harness passes through the firewall.
8. Review TSBs: Check for Technical Service Bulletins like PIT4730B, which provides specific diagnostic advice for intermittent communication loss and warns against unnecessarily replacing the BCM.

Parts You'll Likely Need

• Transmission Control Module (TCM) (OEM #ACDelco 24252114 (for 4-speed) or part of TEHCM for 6-speed (e.g., 24256861, 24260028 - verify by VIN))

Related Codes That Often Appear With This One

• U0100 — Lost Communication with ECM. This often appears with U0073 because when the entire network is down, no modules can talk to the engine computer.
• U0101 — Lost Communication with TCM. This is a very strong indicator that the Transmission Control Module or its wiring is the root cause of the network failure.
• U0121 — Lost Communication with ABS Control Module (EBCM). This indicates the brake control module is also offline, which is expected when the whole bus is down.
• P0700 — Transmission Control System (MIL Request). This code is sent by the TCM to the ECM to request the Check Engine Light be turned on. It indicates a fault within the transmission system and is almost always present when the TCM is the cause.

Technical Service Bulletins (TSBs) & Recalls

• PIT4730B: Warns that intermittent shorts on the GMLAN circuits (often from chafing) can cause the BCM to appear offline for an entire ignition cycle, leading to a misdiagnosis of a failed BCM when the wiring is the actual fault.
• 14404B: Special coverage for 2008-2009 models with the 6T70/6T75 transmission for a fractured 3-5-R wave plate, a separate but common transmission issue on this platform.
• 08-07-30-021H: A general TSB for GM LAN communication issues that points to checking for chafed wiring and backed-out terminals in harness connectors, especially the transmission connector.

Platform-Specific Known Issues

• TCM Location and Heat Failure: The Transmission Control Module is located inside the transmission housing, integrated with the valve body. This location subjects it to constant high temperatures and vibration, which contributes to a high failure rate of the internal electronics, causing it to short out the communication bus.
• Wiring Harness Chafing Points: The main engine harness has a tendency to rub against the transmission case, engine mounting brackets, or the firewall. Over time, this can wear through the insulation on the CAN bus wires (Twisted Pair, typically Tan and Tan/Black) and cause them to short to each other or to ground.
• Grounding Sensitivity: These vehicles are notoriously sensitive to poor ground connections. A loose or corroded main ground strap between the battery, chassis, and engine block can cause fluctuating voltages that are sufficient to knock communication modules offline, triggering a U0073 code without any other 'hard' part failure.

Mechanic-Grade Diagnostic Values

• High-Speed GMLAN Bus Resistance — expected: Approximately 60 Ω. Failure: 120 Ω indicates an open circuit or one terminating resistor is offline. ~0 Ω indicates the CAN High and CAN Low wires are shorted together.
• High-Speed GMLAN High Wire Voltage (TAN/BLK) — expected: ~2.5V at rest (recessive), ~3.5V when active (dominant). Failure: Voltage stuck high, low, or at 0V indicates a short or open.
• High-Speed GMLAN Low Wire Voltage (TAN) — expected: ~2.5V at rest (recessive), ~1.5V when active (dominant). Failure: Voltage stuck high, low, or at 0V indicates a short or open.

Hidden / Shadow Codes Worth Checking

• U0073 71: A GM-specific symptom code indicating the Control Module Communication Bus is Off with a symptom byte of 71 (Invalid Serial Data Received). (see via This code is typically visible with a dealership-level scan tool like a GM Tech 2 or GDS2. It is often stored as a history code in multiple modules on the high-speed bus.)
• U0140 00: Lost Communication With Body Control Module. TSB PIT4730B links this code directly with U0073, noting that an intermittent wiring short can cause the BCM to go offline for an entire ignition cycle, triggering both codes. (see via Visible with most advanced scan tools that can communicate with all vehicle modules.)

Scan Tool Commands That Help

• GM Tech 2 / GDS2 / J2534 Pass-Thru: Module Status / Network Test — This is the initial step to see which modules are actively communicating on the network and which are offline. This helps narrow down if the fault is global (affecting all modules) or isolated to one module not responding.
• GM SPS (Service Programming System): Module Programming/Setup — This is mandatory after replacing the TCM (TEHCM) or BCM. The new module must be programmed with the vehicle's VIN and specific configuration files. Failure to program will result in a no-start condition or persistent communication codes.
• GM Tech 2 / GDS2: Crankshaft Position Variation Learn — Often required after programming the ECM or TCM. If not performed, a P0315 code may set, and engine performance may be affected.

Wiring & Ground Locations

• GMLAN HS Wires — Twisted pair of TAN (CAN Low, Circuit 2501) and TAN/BLK (CAN High, Circuit 2500) wires running between all high-speed modules.. These are the two wires that form the communication backbone. A short between them, or a short from either to ground/power, will cause a U0073.
• G203 — Under the center console, near the Body Control Module (BCM).. This is a primary ground point for the BCM. A poor connection here can cause the BCM to malfunction and disrupt the network.
• G103 — On the left rear of the engine compartment.. Serves as a ground point for several engine-area components. A loose or corroded G103 can introduce electrical noise or voltage drops affecting the ECM.
• TCM Connector — The main 16-pin pass-through connector on the driver's side of the transmission case for 6-speed models.. This is a critical failure point. It carries the GMLAN signals, power, and ground to the internal TEHCM. Corrosion or damaged pins here will mimic a complete TEHCM failure.
• BCM — Located under the center console, often integrated with the passenger compartment fuse block.. The BCM is one of the two terminating resistors for the high-speed CAN bus (the ECM is the other). If the BCM loses power or ground, its 120-ohm resistor is removed from the network, changing the bus resistance to 120 ohms and causing instability.

Real Owner Repair Stories

• BobIsTheOilGuy forum user 'userfriendly' (2011 GM Truck with Allison 1000 (demonstrates a similar TEHCM failure and programming issue)) — Vehicle went into limp mode, lost the PRNDL gear indicator display, and multiple warning lights came on.
  ❌ Tried (didn't work) Resetting codes with a tuner worked only temporarily (for 5 minutes). A professional Snap-On scanner could not program the new replacement TCM to the vehicle's VIN.
  ✅ What actually fixed it The vehicle had to be taken to a GM dealership to have the new, updated-part-number TCM programmed ('flashed') to the vehicle. This resolved all issues.
• NHTSA ODI #10566655 — An owner reported that their gauges "went nuts" and the vehicle started shifting hard. While a dealership initially replaced terminals to address codes including U0073, the issue recurred the following day.
• NHTSA ODI #11244385 — A driver experienced a loss of engine power and a bucking sensation accompanied by codes P0700 and U0073. The instrument cluster gauges, including the odometer and RPM, behaved erratically during the failure.

"I Checked Everything" — The Actual Cause

• The most common 'looks good but isn't' scenario for U0073 on this platform is described in GM TSB PIT4730B. A technician may find the BCM is not communicating and condemn the module. However, the true cause is often an intermittent short-to-ground or short-between-wires in the CAN bus harness, frequently triggered by bumps. This short causes the BCM to go into a 'bus off' state for the entire ignition cycle. The BCM itself is fine, but it won't talk again until the car is shut off and the module powers down completely, which can take up to 20 minutes. The fix is to find and repair the wiring short, not replace the BCM.

OEM Part Supersession History

• 24256861 (for 6-speed TEHCM) → 19431596 — The original TEHCM had a high failure rate. The superseding part is an updated design intended to be more durable.
  Heads up: A used module with an old part number may be prone to the same original failure. Programming by a GM dealer is often required for the new part to be recognized by the vehicle.

Model Year Variations Within This Range

• 2008-2012: The primary difference affecting this code is the transmission type. Models with the 6-speed automatic (6T40 or 6T70, common with 2.4L and standard on 3.6L) use an internal TEHCM (TCM/solenoid assembly) which is a very common failure point. Models with the 4-speed automatic (4T45, found on some 2.4L models) use a separate, externally mounted TCM that is generally more reliable.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Timing Chain Stretch (2.4L and 3.6L Engines) 🔴 High — Common after 80,000-120,000 miles. The 3.6L V6 (LY7) is particularly infamous for this, often setting a P0008 code. The 2.4L Ecotec is also affected by tensioner and guide failures. (Ref: Special Coverage Adjustment #11340C was issued for the 3.6L V6.)
• 6T70/6T75 Transmission 3-5-R Wave Plate Failure 🔴 High → Shop Transmission Assembly — Common in 2008-2009 models, leading to loss of 3rd, 5th, and Reverse gears. Often requires a transmission rebuild. (Ref: TSB 14404B provided special extended coverage, which is now expired.)
• Electric Power Steering (EPS) Failure 🟠 Medium — Sudden loss of power steering assist was common enough to warrant a recall. The driver would receive a DIC message and the steering would become very heavy at low speeds. (Ref: Recall N140115 (GM Bulletin 14116/14117/14118 depending on build date).)
• Excessive Oil Consumption (2.4L Ecotec) 🟠 Medium — Some 2.4L engines may consume excessive amounts of oil due to piston ring issues, leading to low oil levels that can accelerate wear on other components like timing chains.
• Cracked Exhaust Manifold (2.4L Engine) 🟡 Low — The factory cast iron exhaust manifold is prone to cracking, causing a loud exhaust leak that sounds like a tractor.
• Door Lock Actuator Failure 🟡 Low — A very common annoyance where one or more door lock actuators fail, preventing the door from locking or unlocking with the remote or interior switch.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used wiring harness from a junkyard is a smart choice if the original is damaged beyond simple repair, provided the donor harness is inspected for cuts, corrosion, or broken connectors. Used BCMs or ECMs can also be cost-effective, but only if you have pre-arranged for a shop with GM SPS software to program the used module to your car's VIN; otherwise, it is a paperweight.

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

What to inspect on the donor part:

• For wiring harnesses: Check for flexible, non-brittle insulation. Inspect major connectors for green/white corrosion on pins. Ensure locking tabs are intact.
• For modules (BCM/TCM/ECM): Look for an intact case with no signs of being pried open. Check for clean connector pins and no evidence of water marks or corrosion on the housing.

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

• Transmission Control Module (TEHCM for 6-speed): Given the high failure rate of the original design and the complexity of the part, using a new OEM (ACDelco) superseded part is strongly recommended over aftermarket or used options. This ensures you get the latest design revisions and reduces the risk of programming incompatibility.

Brands owners have reported issues with on this vehicle:

• While brands like Dorman offer TEHCM replacements, forum discussions are mixed. Given the labor to install (inside the transmission), risking an aftermarket part that may have a shorter lifespan or programming quirks is generally not advised by master technicians.

Real Owner Stories

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

Documented NHTSA Reports

Related OBD-II Codes

• U0101 — Lost Communication with TCM; frequently appears with U0073 when the Transmission Control Module or its wiring is the source of the bus failure.
• P0700 — Transmission Control System Malfunction; a generic code indicating the TCM has requested the MIL, often seen when the TCM is experiencing communication or internal hardware issues.
• P0722 — Often mentioned in the context of transmission-related communication failures and TCM issues on this platform.

Frequently Asked Questions