U0073 on 2018-2022 Honda Insight: Control Module Communication Bus 'A' Off Fixes

What's Unique About the 2018-2022 Honda Insight

The third-generation Insight is a highly integrated hybrid vehicle, making it very sensitive to network communication issues. A major recall (NHTSA 20V-771) was issued for the 2019-2020 Insight due to a BCM software flaw that could disrupt network communication and cause widespread electrical failures. This, along with dealer bulletins to investigate BCM-related DTCs, confirms that module communication is a known weak point on this platform.

Symptoms You May Notice

• Multiple warning lights illuminated on the dashboard simultaneously (Check Engine, VSA, ABS, Power Steering, Brake System)
• Vehicle may not start or may be stuck in Park
• Loss of power steering assist
• Erratic or blank instrument cluster gauges
• Engine may run rough or stall
• Malfunction of wipers, turn signals, or rearview camera

Most Likely Causes

1. Weak or Failing 12V Battery 🔴 High Probability Modern vehicles with numerous electronic modules require stable voltage. A weak battery can cause voltage to drop during startup, preventing modules from initializing correctly and causing network communication to fail. This is a very common first point of failure for complex electrical issues. 🎬 See this guide on common symptoms of a bad battery
   How to confirm: Test the 12V battery with a multimeter or a professional battery tester. Voltage should be above 12.4V at rest and 13.8-14.5V while the vehicle is in 'Ready' mode. A load test is the most definitive way to confirm battery health.
   Typical fix: Recharge or replace the 12V auxiliary battery.
   Est. part cost: $150-$300
2. Faulty Vehicle Stability Assist (VSA) / ABS Modulator 🟡 Medium Probability The VSA/ABS module is a central node on the F-CAN bus. An internal electronic failure of this module can disrupt the entire network, a common failure pattern on many modern Hondas, including the platform-mate Civic. Its failure often takes the whole network down.
   How to confirm: A professional will use an advanced scan tool to check for communication with all modules. If the VSA/ABS module is the only one not responding or if it has internal fault codes (like U3000-49), it is the likely culprit. The diagnostic process involves disconnecting it to see if communication between other modules is restored.
   Typical fix: Replace the VSA/ABS modulator and perform the necessary programming and calibration procedures using a Honda-specific scan tool.
   Est. part cost: $800-$1500
3. BCM Software Flaw or Failure 🟡 Medium Probability Honda issued a recall (NHTSA 20V-771) for 2019-2020 Insights specifically to update faulty BCM software that could disrupt CAN communication. Even for vehicles outside the recall scope, the BCM remains a critical and complex network component that can fail.
   How to confirm: First, check if your vehicle's VIN is part of recall 20V-771 (Honda campaign X95). If so, the dealer software update is the first step. If not, diagnosis involves using a scan tool to see if the BCM is offline or reporting internal errors. A technician will verify power and ground to the module before condemning it.
   Typical fix: Perform the BCM software update under the recall. If the module has failed hardware, it must be replaced and programmed to the vehicle.
   Est. part cost: $0 for recall software update, $400-$700 for hardware replacement.
4. Wiring Harness Damage or Loose Connection ⚪ Low Probability Some Honda vehicles have been reported to use soy-based wiring insulation, which can attract rodents. Chafing against the chassis or engine components can also damage the twisted pair of CAN bus wires, causing a short or open circuit.
   How to confirm: Visually inspect major wiring harnesses, especially where they pass through the firewall or are near engine components. Check for signs of rodent damage (chewing), chafing, or corrosion at major connectors, including at the BCM and VSA module.
   Typical fix: Repair the damaged section of the wiring harness. This requires carefully splicing, soldering, and protecting the repaired wires.
   Est. part cost: $5-$50 for repair materials, but labor-intensive

Rare But Worth Checking

• Aftermarket Electronics: Poorly installed remote starters, alarms, or audio equipment can interfere with the CAN bus network, causing communication errors. Disconnecting any aftermarket devices is a crucial early diagnostic step.

Diagnosis Steps

1. Check Battery Health: Start with the simplest cause. Test the 12V battery's voltage and perform a load test. Ensure battery terminals are clean and tight. Low voltage is a primary cause of communication codes.
2. Check for Recalls: Enter your VIN on the NHTSA or Honda owner's website to check for open recalls, especially NHTSA recall 20V-771 (Honda campaign X95) for the BCM software update on 2019-2020 models.
3. Scan for All DTCs: Use an advanced OBD-II scanner capable of reading codes from all modules (ABS, BCM, ECM, etc.). Note which modules are not communicating and look for any internal fault codes (like U3000-49).
4. Visual Inspection: Thoroughly inspect the main engine and cabin wiring harnesses for any signs of damage, chafing, or corrosion. Pay close attention to the area around the VSA modulator, BCM, and any aftermarket wiring.
5. Check CAN Bus Resistance: With the battery disconnected, measure the resistance between Pin 6 (CAN-H) and Pin 14 (CAN-L) at the OBD-II port. A healthy network should read approximately 60 ohms. A reading of 120 ohms indicates a missing terminating resistor or a break in the circuit, while 0 ohms indicates a short between the two lines.
🎬 Watch: How to perform a CAN bus resistance check
6. Isolate Modules: If the resistance is incorrect or modules are offline, a technician will begin disconnecting modules one by one from the CAN bus to see if the network comes back online. This helps pinpoint a faulty module that is bringing the network down. The VSA modulator is a common starting point.
7. Professional Diagnosis: If the cause is not obvious, professional diagnosis with a Honda-specific scan tool (HDS) and an oscilloscope is necessary to analyze the data signals on the network directly and perform module programming.

Parts You'll Likely Need

• 12V Auxiliary Battery — A weak or failing battery is a frequent cause of low-voltage conditions that disrupt module communication on modern, electronically-dense vehicles.
  Trusted brands: Honda OEM, Interstate, DieHard
  OEM price range: $200-$300
  Aftermarket price range: $150-$250
• VSA / ABS Modulator Control Unit (OEM #57100-TXM-A53 (Touring, supersedes 57100-TXM-A51, 57100-TXM-A52) or 57100-TXM-A03 (LX, EX).) — This module is a common failure point that can crash the entire CAN network. Its failure often results in a U0073 code accompanied by ABS and VSA warning lights.
  Trusted brands: Honda (OEM), Bosch (often the OE supplier)
  OEM price range: $1000-$1500
  Aftermarket price range: $700-$1200 (often remanufactured)

Related Codes That Often Appear With This One

• U0121 — Lost Communication With Anti-Lock Brake System (ABS) Control Module. This often appears with U0073 when the VSA/ABS module is the component that has failed.
• U0140 — Lost Communication With Body Control Module (BCM). This may be present if the BCM is the source of the network failure.
• U0100 — Lost Communication With ECM/PCM 'A'
• U0155 — Lost Communication With Instrument Panel Cluster (IPC) Control Module
• U3000-49 — Control Module Internal Electronic Failure. This code stored within a specific module (like the VSA) points directly to that module as the source of the problem.

Technical Service Bulletins (TSBs) & Recalls

• APaS10162020909 / APaS09102020910: Internal dealer message

Platform-Specific Known Issues

• A major software recall (NHTSA 20V-771 / Honda X95) affects 2019-2020 Insight models. A flaw in the Body Control Module (BCM) programming can disrupt communication between modules, causing multiple warning lights and the failure of wipers, turn signals, and the rearview camera. This should be the first item checked for affected vehicles.
• Honda has issued internal dealer messages (e.g., APaS10162020909) requesting the collection of data from 2019-2020 Insights with BCM-related DTCs, indicating an ongoing effort to understand electronic module issues on this platform.

Mechanic-Grade Diagnostic Values

• CAN Bus Resistance — expected: ~60 Ohms across Pin 6 (CAN-H) and Pin 14 (CAN-L) of the OBD-II port with the battery disconnected.. Failure: A reading of ~120 Ohms suggests a break in the circuit or a missing terminating resistor. A reading of 0 Ohms indicates a short circuit between the CAN-H and CAN-L wires.
• CAN Bus Voltage — expected: Key on, engine off: CAN-H (Pin 6 to ground) should be ~2.5-3.5V. CAN-L (Pin 14 to ground) should be ~1.5-2.5V.. Failure: A voltage stuck high, low, or at zero on either line indicates a circuit fault or a faulty module transceiver.
• VSA Modulator Power & Ground — expected: With the VSA modulator connector unplugged and key on, there should be battery voltage at the power supply pin (fed by a 10A fuse) and continuity to ground at the ground pin.. Failure: Absence of power or a bad ground prevents the module from operating and communicating.
• CAN Line Continuity Check — expected: With the battery, VSA modulator, and ECM disconnected, there should be continuity between the corresponding CAN-H and CAN-L pins at the VSA connector and the ECM connector.. Failure: No continuity indicates an open/break in the wiring harness between the two modules.

Scan Tool Commands That Help

• Honda Diagnostic System (HDS): ECM/PCM Reset — After reconnecting all components or replacing a module, this function is used to clear learned values and re-initialize the system.
• Honda Diagnostic System (HDS): ETCS Learn Procedure — This procedure is required after performing an ECM/PCM reset to relearn the electronic throttle control system parameters.
• Honda Diagnostic System (HDS) or equivalent: VSA Sensor Neutral Position Memorization — After replacing the VSA/ABS modulator, this calibration procedure must be performed to teach the new module the vehicle's neutral position for the yaw and deceleration sensors. Failure to do this will result in other VSA/ABS related codes.

Wiring & Ground Locations

• VSA Modulator 46P Connector — The main electrical connector on the VSA/ABS modulator assembly, located in the engine bay.. This is the primary connection point for the VSA module. Testing for power, ground, and CAN signals happens here. Poor pin tension in this connector can be a root cause of the fault.
• ECM Connector No. 4 (40P) — One of the main connectors on the Engine Control Module (ECM).. This connector contains the other end of the F-CAN bus wiring from the VSA module. It's used in continuity tests to verify the integrity of the harness between the modules.
• G303 (example) — On similar Honda platforms, a key ground for the VSA system is located on the chassis near the module.. A corroded or loose ground is a common cause of module communication failure. While the exact number for the Insight may vary, checking the main ground bolt for the VSA modulator is a critical step.
• Under-dash Fuse #34 (10A) — In the interior fuse box located under the driver's side dashboard.. This fuse provides key-on power to the VSA/ABS control unit. If this fuse is blown, the module will be offline and cause a U0073 code.

"I Checked Everything" — The Actual Cause

• On a similar Honda platform (2017 Civic) with a VSA modulator no-communication fault, all power, ground, and resistance tests passed. The actual cause was found to be poor pin tension (pin fitment) within the large 46-pin connector for the VSA module. The pins were not making a secure physical connection, causing intermittent communication loss that standard static electrical tests could not detect. The fix was to carefully retension the female pins in the connector to ensure a tight grip on the male pins of the module.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Sticky Steering at Highway Speeds 🔴 High — Widespread on platform-mate 2022-2023 Civics, with some reports on other models. Tends to appear at low mileage, sometimes within the first 10,000 miles. (Ref: TSB 23-037 was issued for 2022-2023 Civics, instructing dealers to replace the EPS gearbox. While not directly for the Insight, it points to a potential issue with the shared steering system design.)
• BCM Software Flaw Causing Widespread Malfunctions 🔴 High — Common enough to trigger a major recall affecting 2019-2020 Insights. (Ref: Recall NHTSA 20V-771 (Honda Campaign X95) was issued to update BCM software that could disrupt communication, causing wipers, lights, and rearview camera to fail.)
• Failing Fuel Pump Causing Stalling 🔴 High — Affected a specific production range of 2019-2020 Insights, leading to a recall. (Ref: Recall NHTSA 20V-314 (Honda Service Bulletin 20-042) was issued because impellers in the fuel pump could deform and cause the pump to fail, leading to engine stalling.)
• DC-DC Converter Failure 🟠 Medium — A recall was issued for 2020-2021 models, indicating a notable failure rate. (Ref: A recall was issued for the 2020-2021 Insight because the DC-DC converter could shut down, preventing the 12V battery from recharging and potentially causing a loss of drive power.)
• Engine Rattles at Cold Start-Up 🟡 Low — Common on many Honda 4-cylinder engines of this era, typically below 40°F. (Ref: TSB 16-012 was issued for other Honda models with similar engines, identifying a defective VTC actuator as the cause. While not specific to the Insight, the symptom and cause are common to the engine family.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used wiring harness from a low-mileage donor vehicle can be a cost-effective option if the original is damaged by rodents or physical impact. It must be thoroughly inspected before purchase.

Donor-vehicle mileage cap: roughly under 50000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For wiring harnesses: Check for any signs of rodent damage (chewed insulation), previous repairs (tape, splices), or brittle/cracked plastic connectors.
• For electronic modules (VSA/BCM): Inspect for any corrosion on the aluminum housing or electrical pins. Avoid any parts from flood-damaged vehicles.

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

• VSA / ABS Modulator Control Unit
• Body Control Module (BCM)

Aftermarket brands forum-validated for this vehicle:

• Module Master (for VSA/ABS module remanufacturing service)

Real Owner Stories

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

Related OBD-II Codes

• U3000-49 — Indicates an internal failure of a module, such as the VSA/ABS modulator, which often causes the wider U0073 communication bus 'off' condition.
• U0122 — Lost communication with the VSA Control Module; frequently appears alongside U0073 when the VSA modulator fails or loses power.
• U0140 — Lost communication with the Body Control Module (BCM), which is a primary suspect in Insight communication failures due to known software flaws.
• U0155 — Lost communication with the Instrument Panel Cluster, often occurring when the CAN bus is disrupted by a faulty VSA or BCM module.

Frequently Asked Questions