U0073

Control Module Communication Bus A Off

Communication / network Generic OBD-II High

What it means

U0073 means the ECM has shut down communication bus "A" because it detected too many errors on the network. When the bus goes off, control modules can no longer share data, which often lights up several warning lamps at once and can trigger limp mode or a no-start. It usually points to a wiring short, a bad connector, or one failed module disrupting the whole network.

High

Can I keep driving? Risky — a bus-off fault can stop control modules talking to each other, which may bring on warning lights, limp mode, or even a no-start; have it diagnosed before driving far.

Real-world scan data

Seen in

2,475

scans in the past year

Found in

0.4%

of scans

0.7%

of scans that found faults

Appears alongside · share of U0073 scans

U0100in 42.5% of scans

U0140in 25.2% of scans

U0121in 22.7% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

Common symptoms

What you'll notice

Multiple warning lights on (ABS, traction, airbag, check-engine)
Several modules unresponsive to a scan tool
Limp mode or reduced power
Possible no-start or intermittent stalling
Erratic gauges or disabled features

Common causes

Most likely first

Short to power or ground on the CAN bus wiring (most common)Likely
Damaged or corroded connector on the communication busCommon
A single failed module dragging the whole bus downCommon
Low battery or charging voltage upsetting the networkLess often
Failed gateway module or ECM/PCMLess often

How to diagnose & fix

Work through it in order

Scan all modules and note which ones have dropped off the bus.
Check battery and charging voltage first — low voltage often trips network codes.
Inspect CAN bus wiring and connectors for shorts, corrosion, or damage.
Isolate a suspect module by disconnecting modules one at a time to see if the bus recovers.
If wiring and modules check out, suspect the gateway or ECM. Clear and retest.

FAQ

Quick answers

Is it safe to drive with U0073?+

Not really. With modules off the bus you can lose safety systems, drop into limp mode, or fail to start — get it diagnosed before relying on the car.

Can I just clear U0073?+

It will usually come straight back while the bus is down. Find and fix the shorted wire or failed module, then clear it.

Read & clear U0073 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX