U0073 on 2012-2017 Subaru Crosstrek: Control Module Communication Bus 'A' Off

What's Unique About the 2012-2017 Subaru Crosstrek

The first-generation Crosstrek (2013-2017) shares its architecture with the Impreza of the same era. While U0073 is a generic code, on these Subarus, it's frequently accompanied by a host of seemingly unrelated warning lights like ABS, Hill Start Assist, and AT Oil Temp. This is because the VDC (ABS) module is a central communication hub, and when it has issues, it can disrupt the entire network, leading to a cascade of communication faults. Owners often report these issues appearing intermittently, sometimes triggered by bumps or cold weather. Critically, a widespread and recalled issue with the brake light switch can also illuminate the ABS and VDC lights, which can be misdiagnosed as a more severe CAN bus fault. In some instances, as noted in NHTSA ODI #11723030, a CAN bus communication fault like U0073 can affect multiple vehicle safety systems simultaneously, including the electronic power steering (EPS).

Symptoms You May Notice

• Check Engine Light is on
• ABS, Vehicle Dynamics Control (VDC), and Hill Start Assist warning lights are on
• Flashing 'AT Oil Temp' light
• Cruise control light flashing or inoperative
• Erratic or harsh transmission shifting
• Hesitation or difficulty accelerating
• Engine may stall or fail to start
• Speedometer and tachometer may freeze or behave erratically
• A/C compressor may not engage or stop working
• Electronic Power Steering (EPS) fault codes or steering concerns

Most Likely Causes

1. Weak or Failing Battery / Poor Charging System 🔴 High Probability → Shop Vehicle Battery Control modules require a stable voltage to initialize and communicate properly. Low voltage during startup is a very common cause of network communication codes on many modern vehicles, and this Crosstrek generation is noted for having battery drain issues.
   How to confirm: Test the battery voltage with a multimeter. It should be ~12.4V+ with the engine off and 13.8V-14.5V with the engine running. Have the battery and alternator tested at an auto parts store. Perform a parasitic draw test if the battery repeatedly dies.
   Typical fix: Replace the battery and ensure battery terminals are clean and tight.
   Est. part cost: $150-$300
2. Damaged Wiring or Loose/Corroded Connectors 🟡 Medium Probability Vibrations, moisture, rodent damage, or previous improper repairs can compromise the CAN bus wiring harness. The CAN bus consists of a twisted pair of wires that are sensitive to damage.
   How to confirm: Visually inspect the wiring harnesses between the ECM, TCM, and VDC/ABS module for any signs of damage, corrosion, or loose connections. Pay close attention to grounds and connectors near each module. A professional would use a multimeter to check for 60 ohms of resistance across the CAN High (Pin 6) and CAN Low (Pin 14) at the OBD-II port to verify network integrity. 🎬 See how to test CAN bus resistance with a multimeter.
   Typical fix: Repair the damaged section of the wiring harness and clean or re-secure any loose connectors. Apply dielectric grease to protect connections.
   Est. part cost: $10-$100
3. Faulty ABS/VDC Control Module 🟡 Medium Probability → Shop ABS Control Module On this platform, the VDC module is a common point of failure that can disrupt the entire CAN network, causing a U0073 code. This is often seen with related C-codes or U0122 for the VDC system.
   How to confirm: This requires a professional scan tool to see if the VDC module is offline or failing to communicate. A technician may disconnect the module to see if communication between other modules is restored.
   Typical fix: Replace the ABS/VDC control module and have it programmed to the vehicle. This is not a simple plug-and-play part.
   Est. part cost: $400-$800
4. Faulty Brake Light Switch 🟡 Medium Probability → Shop Brake Light Switch A widespread recall was issued for this switch on 2013-2017 models. Its failure causes nearly identical warning lights (ABS, VDC, Hill Assist) as a CAN fault and can prevent the car from shifting out of Park.
   How to confirm: With the car on, have someone press the brake pedal while you observe if the brake lights illuminate. If they do not, the switch is a primary suspect. The car may also be stuck in Park.
   Typical fix: Replace the brake light switch located at the top of the brake pedal arm. It is an inexpensive and relatively simple DIY repair. 🎬 Watch: How to replace the recalled brake light switch.
   Est. part cost: $25-$50

Rare But Worth Checking

• Faulty ECM or TCM: While less common than the VDC module, a failure in the Engine or Transmission Control Module can also bring down the network. Diagnosis involves isolating the faulty module, often by disconnecting it to see if the network comes back online.
• Faulty Body Control Module (BCM): → Shop Body Control Module The BCM is another key module on the CAN bus. A failure here can cause a U0073 code along with other strange electrical issues.
• Interference from Aftermarket Electronics: Improperly installed remote starters, alarms, stereos, or even incompatible LED bulbs can introduce noise onto the CAN bus network and cause communication errors. If the problem started after an installation, this is a likely cause.

Diagnosis Steps

1. Check for any other stored DTCs. Codes that point to a specific module (like U0122 for the VDC) are a huge clue.
2. Check Brake Light Function. Have a helper confirm if your brake lights work when you press the pedal. If not, suspect the recalled brake light switch.
3. Check the battery. Ensure it is fully charged and the terminals are clean and tight. Test the charging system. A weak battery is a very common trigger.
4. Inspect all related fuses for the ECM, TCM, and VDC systems.
5. Perform a thorough visual inspection of the wiring harnesses connecting the major control modules. Look for any chafing, corrosion, rodent damage, or loose connectors, especially around the ABS module and main fuse box.
6. Check major ground points under the hood and in the driver's kick panel area for corrosion or looseness. Pay special attention to the main engine ground strap and the ECU grounds on the intake manifold.
7. If you have a multimeter, you can perform a basic network integrity check. With the battery disconnected, measure the resistance between Pin 6 (CAN High) and Pin 14 (CAN Low) on the OBD-II port. A healthy network should read approximately 60 ohms.
8. If the above steps don't reveal the issue, the vehicle should be taken to a professional. They will use a scan tool to see which modules are online and may use an oscilloscope to check the CAN signal waveform to isolate the fault.

Parts You'll Likely Need

• ABS/VDC Control Module — This module is a frequent failure point on this platform that can cause a network-wide communication fault. Part number is VIN-specific.
  Trusted brands: Subaru (OEM)
  OEM price range: $600-$800
  Aftermarket price range: $400-$600
• Battery — Low system voltage is a primary trigger for communication codes.
  Trusted brands: Interstate, DieHard, Duralast
  OEM price range: $200-$300
  Aftermarket price range: $150-$250
• Brake Light Switch (OEM #83311FG001 (superseded part)) — A recalled part that commonly fails, causing ABS/VDC warning lights that mimic a CAN failure. An easy and inexpensive first check.
  Trusted brands: Subaru (OEM), Beck/Arnley
  OEM price range: $30-$50
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• U0122 — Lost Communication with Vehicle Dynamics Control Module. This code often appears with U0073 and strongly suggests the VDC module or its wiring is the source of the network problem.
• U0100 — Lost Communication With ECM/PCM 'A'. This indicates a more severe network failure where the main engine computer is offline.
• U0101 — Lost Communication with TCM. This code is likely to appear when symptoms include erratic transmission shifting.

Technical Service Bulletins (TSBs) & Recalls

• TSB 02-157-14R: Addresses excessive oil consumption on FB20 engines, outlining the oil consumption test procedure and the potential for short block replacement under an extended warranty.
• TSB 05-70-19: Pertains to premature rear wheel bearing failure on Crosstrek, Impreza, and Forester models due to a misshapen rear wheel backing plate.

Platform-Specific Known Issues

• A recall was issued for the brake light switch on 2013-2017 Crosstreks. Failure of this switch causes ABS and VDC warning lights, which can be easily misdiagnosed as a U0073 network fault.

Mechanic-Grade Diagnostic Values

• CAN Bus Network Resistance — expected: ~60 Ω. Failure: A reading of ~120 Ω indicates an open circuit or a missing terminating resistor (faulty module). A reading near 0 Ω indicates a short between CAN High and CAN Low wires.
• CAN High (Pin 6) Voltage to Ground — expected: ~2.5V (recessive state), ~3.5V (dominant state). Failure: Voltage stuck high, low, or at 0V indicates a short or open on the line.
• CAN Low (Pin 14) Voltage to Ground — expected: ~2.5V (recessive state), ~1.5V (dominant state). Failure: Voltage stuck high, low, or at 0V indicates a short or open on the line.
• VDC Control Module Power Supply — expected: 10 – 15 V. Failure: Low or no voltage indicates a power supply issue to the module, not necessarily an internal module fault.

Scan Tool Commands That Help

• Subaru Select Monitor (SSMIII/SSM4): Each System Check / All Systems Diagnosis — To perform an initial network health check and identify which specific control modules are not communicating with the scan tool. This is the first step in isolating the fault.
• Subaru Select Monitor (SSMIII/SSM4): Parameter Selection / Registration — This is a mandatory procedure after replacing the VDC Control Module. The new module must be registered to the vehicle's specific configuration. Failure to perform this step will result in a 'Parameter selection error' DTC and continued warning lights.
• Subaru Select Monitor (SSMIII/SSM4): VDC Sensor Midpoint Setting Mode — After replacing the VDC module or related sensors, this function is used to calibrate the steering angle and G-sensors to their neutral positions.

Wiring & Ground Locations

• CAN Bus Junction Connector — On many Subarus of this era, a key CAN joint connector is located behind the dashboard, often to the left of the steering column or near the main fuse panel.. This connector is a central point where multiple CAN bus branches meet. Corrosion or a loose pin in this single connector can take down the entire network, causing a U0073 code.
• Intake Manifold Ground — Bolted directly to the top of the engine's intake manifold.. On Subarus, the Engine Control Module (ECM) receives its primary ground reference from this point. A loose or corroded connection here can cause unstable ECM operation and lead to network communication codes like U0073. This is especially problematic if TGV deletes or spacers have been installed without providing an alternate ground path.
• Main Chassis Ground — A braided ground strap typically located on the driver's side frame rail, connecting the engine block to the chassis, often near the front of the tire.. A corroded or broken main engine-to-chassis ground strap forces electrical current to find alternate, higher-resistance paths, which can introduce noise and voltage drops that disrupt sensitive module communications.
• GB-11 / GB-12 — These are ground distribution points shown in wiring diagrams, likely located in the main cabin or engine bay harnesses. The VDC Control Module is listed as being connected to these grounds.. If a fault is traced to the VDC module, checking the integrity of its specific ground points (GB-11/12) is a critical step before replacing the expensive module itself.

Real Owner Repair Stories

• Reddit user on r/subaru (2016 Subaru Crosstrek CVT) — U0073 code appeared with TC and Cruise control lights on, rough idle, erratic transmission ratio changes, and the A/C compressor would not engage for more than a second.
  ❌ Tried (didn't work) Replacing newly installed LED boomerang/side marker bulbs with incandescent bulbs (12V3W instead of the original 12V5W).
  ✅ What actually fixed it Performing a full reset by disconnecting the negative battery terminal. This suggests the CAN bus modules were in a fault state due to the electrical change from the LED bulbs and required a hard reboot to restore normal communication.
• NHTSA ODI #11723030 — An owner reported a safety critical steering concern involving electronic power steering (EPS) fault codes. The report noted a CAN bus communication fault U0073 affecting multiple vehicle safety systems simultaneously.

OEM Part Supersession History

• 83311FG000 → 83311FG001 — Updated design to address high failure rates that led to a recall (WUE-90).

Model Year Variations Within This Range

• 2014-2017: The XV Crosstrek Hybrid model was introduced. While it shares the same basic CAN bus architecture, it includes additional high-voltage systems and a different CVT. Diagnosis of the CAN bus on a Hybrid model may be more complex due to the interaction with the hybrid control module, and service of orange high-voltage cables requires specialized training and safety equipment.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Excessive Oil Consumption (FB20 Engine) 🔴 High — Common in 2012-2015 models. Caused by faulty piston rings. Consumption can exceed 1 quart per 1,200 miles. (Ref: TSB 02-157-14R. Subaru extended the powertrain warranty to 8 years/100,000 miles for this issue and would perform an oil consumption test, potentially leading to a short block replacement.)
• Lineartronic CVT Failure / Shudder 🔴 High — Prevalent in 2013-2015 models. Symptoms include shuddering, hesitation from a stop, jerking, and complete failure. Often caused by a faulty torque converter lock-up solenoid in the valve body. (Ref: Subaru extended the CVT warranty to 10 years/100,000 miles for many affected vehicles due to widespread issues.)
• Premature Wheel Bearing Failure 🟠 Medium — Very common, especially for rear wheel bearings, which can fail as early as 30,000-40,000 miles. Symptoms include a humming or roaring noise that increases with speed. (Ref: TSB 05-70-19 addresses this issue, which was caused by a defectively shaped rear wheel backing plate allowing water intrusion.)
• Faulty Brake Light Switch 🟡 Low → Shop Brake Light Switch — Extremely common across 2013-2017 models. The switch fails, causing the brake lights to not illuminate and triggering ABS, VDC, and Hill Assist warning lights. (Ref: Subaru issued a recall for this component. The failure can prevent the vehicle from being shifted out of Park.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this repair, obtaining used parts is generally not recommended for control modules. However, it can be a cost-effective option for purely mechanical or simple electrical components like the brake light switch or sections of wiring harness pigtails if a connector is damaged.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For wiring: Check for any signs of brittleness, cracking in the insulation, or previous splice repairs.
• For connectors: Ensure locking tabs are intact and pins are not corroded or bent.
• Verify the donor vehicle is from a dry climate to minimize the risk of corrosion.

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

• ABS/VDC Control Module: This part is VIN-specific and requires programming and calibration with the Subaru Select Monitor tool. A used module from another vehicle is highly unlikely to work correctly and may not be programmable.
• ECM/TCM: Similar to the VDC module, these are critical computers that are coded to the vehicle's immobilizer and specific options. A used part will typically prevent the car from starting.

Aftermarket brands forum-validated for this vehicle:

• Brake Light Switch: Beck/Arnley, Standard Motor Products (SMP).

Brands owners have reported issues with on this vehicle:

• Unknown/no-name electronics from online marketplaces, especially LED bulbs that are not advertised as 'CAN bus compatible' or 'error-free', as these are known to cause interference.

Real Owner Stories

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

Related OBD-II Codes

• U0122 — Lost Communication with VDC Control Module — often appears alongside U0073 when the VDC module is the specific component disrupting the CAN bus.
• C-CODES — Chassis codes related to the VDC/ABS system frequently accompany U0073 because the VDC module is a common failure point on this platform.
• P0000 — Generic powertrain codes may appear if the ECM or TCM cannot communicate properly due to the bus being 'off' (U0073).
• U0101 — Lost Communication with TCM — may occur if the CAN bus failure prevents the Transmission Control Module from sending or receiving data, leading to the erratic shifting symptoms described.

Frequently Asked Questions