U0073: Control Module Communication Bus A Off
Key takeaways
- U0073 means a control module saw so many errors on the car's main data network (the CAN bus) that it stopped talking on it.
- Drive short trips only if the car starts and runs normally; if it won't start, stalls or loses power steering, have it towed.
- Most U0073 fixes are electrical: a weak battery, a loose terminal, a bad ground or a wet or damaged connector come before any module.
- One failing module or an add-on device can drag the whole network down, so a shop unplugs modules one at a time before replacing anything.
- 34 owner complaints filed with NHTSA mention U0073, and 73 manufacturer bulletins from 4 makes name it.
What U0073 means
A computer in your car saw so many garbled messages on its data network that it switched itself off that network. Scanners call it “Control Module Communication Bus A Off” (some show “Bus Off”). Modern cars link the engine, transmission, ABS, body and instrument cluster computers over a two-wire network called the CAN bus. Every module checks each message it sends and receives. When a module counts too many errors in a row, it goes “bus off” on purpose so it doesn’t jam the network for everyone else, and stores U0073.
The code doesn’t say which wire or module caused the errors. It usually comes with other lost-communication codes, because once the network is noisy or shorted, several modules stop hearing each other at the same time.
Is it safe to drive?
Short trips only, and only if the engine starts and runs normally. With the network down or unstable, the transmission may fall back to one gear, stability control and ABS can switch off, and gauges can freeze or drop to zero. That makes highway driving a bad idea until it’s checked.
The answer becomes no if the car won’t start, stalls, or loses power steering while driving. On cars with electric power steering, a network fault can take the assist away, and a stall at speed takes power assist off the brakes too. Have it towed. If the only sign is a stored code after a battery change or jump start, the car may be fine; see below.
Causes, ranked
| Cause | How you confirm it | Typical cost (US independent shop, 2026) |
|---|---|---|
| Weak battery or low voltage during cranking | Battery load test; code appeared after a jump, a flat battery or a cold start | $0 if it only needed a charge; $150–$350 for a battery |
| Loose or corroded battery terminals, engine or body grounds | Voltage drop test across cables and ground straps; crust at the posts | $20–$120 |
| Wet, corroded or damaged network connector or wiring | Resistance across the two network pins at the diagnostic port (about 60 ohms on most cars, battery disconnected); look for water, green corrosion or chafed wires | $100–$180 to diagnose; $100–$250 to repair |
| Add-on device on the network (remote starter, trailer module, plug-in tracker or code reader left in the port) | Unplug it and see if the code stays away | $0 to remove |
| One failing module shorting the network | Shop unplugs modules one at a time and watches the network recover | $500–$1,500 for most modules; $800–$1,800 plus programming for an engine computer |
| Module software fault | A bulletin covers your make, model and year; shop reflashes | $100–$200 |
What to check first
- Test the battery and charging system. A healthy battery rests near 12.6 volts and running voltage usually sits between about 13.5 and 14.7. Our battery keeps dying guide walks through it.
- Clean and tighten the terminals and grounds, including the engine-to-body ground straps.
- Unplug anything added to the car: a plug-in insurance or fleet tracker, an aftermarket remote starter, a trailer brake controller. Add-ons wired into the network are a common source of bus errors.
- Read codes from every module. Which modules logged U0073 and which ones went silent tells a shop where on the network to look. Our guide to reading check engine codes covers the basics; many cheap readers only see the engine computer.
- Clear it and drive only if the car runs normally. If it doesn’t return in a week, a voltage dip is the likely cause.
- Ask about bulletins before a module is ordered. Nearly all of the bulletins are GM: several direct dealers to inspect the engine harness for shorting on 2019–2021 Silverado and Sierra 1500 trucks, and others cover gauges, radio and warning lights dropping out with multiple network codes on Silverado, Sierra, Tahoe, Yukon, Escalade and Trax.
34 owner complaints filed with NHTSA mention U0073. The Toyota Camry leads with 6, four of them 2007 models, followed by the Chevrolet Equinox with 4. These are owner reports, not confirmed defects.
What it costs
The cheap outcome is a battery charge, a cleaned terminal or an unplugged add-on, $0–$120. The common outcome is a new battery or a connector or wiring repair, $100–$350 plus diagnosis. The expensive outcome is a replacement module: $500–$1,500 for most, and $800–$1,800 plus programming if it’s the engine computer. Network testing at $100–$180 is what stops you from buying a module that was never the problem. If you want help reading your codes before you book, ask our AI mechanic.
Related codes
U0073 almost always travels with lost-communication codes such as U0100 (engine computer), U0101 (transmission computer) and U0121 (ABS module), and sometimes with U0001 for the high-speed network itself. Several at once points to shared power, ground or network wiring, not several failed modules.
What owners report to NHTSA
34 complaints filed with NHTSA mention U0073, 29 of them since 2015, across 17 different models. The component owners most often filed it under: electrical system.
Most-reported models
| Vehicle | Complaints | Model years reported |
|---|---|---|
| TOYOTA CAMRY | 6 | 2007, 2009, 2018 |
| CHEVROLET EQUINOX | 4 | 2011, 2012, 2013 |
| CHEVROLET SILVERADO 1500 | 3 | 2008, 2011, 2014 |
| CHEVROLET MALIBU | 3 | 2018, 2020, 2023 |
Manufacturer service bulletins that name U0073
73 technical service bulletins and manufacturer communications filed with NHTSA mention U0073, from 4 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:
- CHEVROLET SILVERADO 1500 (2019, 2020, 2021), bulletin 10193465: This Preliminary information communicates the following issues and directs dealership to inspect the engine harness for shorting. Some customers may comment on any of the following concerns: - SES MIL - No Start - No Cra…
- GMC SIERRA 1500 (2019, 2020, 2021), bulletin 10193465: This Preliminary information communicates the following issues and directs dealership to inspect the engine harness for shorting. Some customers may comment on any of the following concerns: - SES MIL - No Start - No Cra…
- CADILLAC ESCALADE (2017, 2018, 2019, 2020), bulletin 10173683: This Preliminary information communicates a customer concern ofIPC gauges inoperative or fluctuate, No Start,No Crank,SIR Light / Service Airbag Message, Service Suspension Message,Radio display blank, Steering Wheel Con…
- CHEVROLET TRAX (2015, 2016, 2017, 2018), bulletin 10178956: This technical bulletin provides repair information to correct a customer concern of Malfunction Indicator Lamp (MIL) illuminated, intermittent service messages, Erratic Gauges and technician finding DTCs U0073, U0121, U…
- CHEVROLET SILVERADO (2017, 2018, 2019), bulletin 10144472: This Preliminary information communicates a customer concern ofIPC gauges inoperative or fluctuate, No Start,No Crank,SIR Light / Service Airbag Message, Service Suspension Message,Radio display blank, Steering Wheel Con…
- GMC SIERRA (2017, 2018, 2019), bulletin 10144472: This Preliminary information communicates a customer concern ofIPC gauges inoperative or fluctuate, No Start,No Crank,SIR Light / Service Airbag Message, Service Suspension Message,Radio display blank, Steering Wheel Con…
Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.
Frequently asked questions
Can a bad battery cause U0073?
Yes. When voltage sags during cranking or after a battery goes flat, modules can drop off the network and log U0073 along with a handful of lost-communication codes. Test the battery and charging system first, especially if the code appeared after a jump start or on a cold morning.
Can I clear U0073 and keep driving?
If the car starts and runs normally, clearing it once is a fair test. If it stays gone for a week of normal driving, it was most likely a one-time voltage dip. If it comes back, or comes with stalling, a no-start or several warning lights, the network needs a proper diagnosis.
Does U0073 mean a module is bad?
Not usually. It means the network was too noisy or shorted for a module to keep talking. A damaged wire, a wet connector, a bad ground or an add-on device plugged into the network cause it more often than a failed module. A module is replaced only after it's shown to be the one pulling the network down.
What are the symptoms of U0073?
Usually several things at once: many warning lights, gauges that drop to zero or flicker, a blank radio, stability control off, a transmission stuck in one gear, and on some cars a no-crank or no-start. It can also sit as a stored code with no symptoms after a battery event.