U0056

Vehicle Communication Bus D Performance

Q: Is it safe to drive with U0056?

Usually yes, but intermittent bus faults can disable systems unpredictably, so get it diagnosed rather than ignoring it.

Q: Can I just clear U0056?

You can, but a performance fault reflects a marginal connection or failing module and will return until that's corrected.

Communication network (CAN bus) Generic OBD-II Medium

What it means

U0056 means communication Bus D is working but not reliably — messages are delayed, corrupted, or dropping out, usually from high resistance, a marginal connection, or a module sending bad data. Because it's an intermittent "performance" fault rather than a dead bus, symptoms tend to come and go. Which features are affected depends on what "Bus D" carries on your specific vehicle.

Medium

Can I keep driving? Usually drivable, but degraded bus performance can make modules drop in and out — expect intermittent warning lights and features until it's fixed.

Real-world scan data

Seen in

scans in the past year

Found in

<0.1%

of scans

<0.1%

of scans that found faults

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

Intermittent warning lights across different systems
Modules on Bus D dropping out and reconnecting
Features that work sometimes and fail other times
Slow or unreliable scan-tool communication with some modules

Common causes

Most likely first

High resistance or a loose connection in the Bus D wiring or connectorsLikely
Corroded, chafed, or partially broken bus wiringCommon
A failing module sending bad data and disrupting bus trafficCommon
Marginal or damaged termination resistor affecting signal qualityLess often
Water intrusion or a weak battery causing erratic communicationLess often

How to diagnose & fix

Work through it in order

Scan all modules and watch for units that intermittently drop off Bus D.
Check battery voltage and charging; correct low voltage, then clear and re-test.
Wiggle-test and inspect Bus D connectors and wiring for corrosion, looseness, or damage.
Measure bus resistance (should be about 60 ohms across the pair) to check termination.
Isolate modules one at a time to find a unit flooding the bus with bad data; repair wiring or replace the confirmed module.

FAQ

Quick answers

Is it safe to drive with U0056?+

Usually yes, but intermittent bus faults can disable systems unpredictably, so get it diagnosed rather than ignoring it.

Can I just clear U0056?+

You can, but a performance fault reflects a marginal connection or failing module and will return until that's corrected.

Read & clear U0056 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