U0027

Low Speed CAN Communication Bus (-) shorted to Bus (+)

Communication network (CAN bus) Generic OBD-II Medium

What it means

U0027 means the negative and positive wires of the low-speed CAN bus are shorted together, which can bring down communication across that whole network. The low-speed bus typically carries body and comfort systems, so the usual result is warning lights and dead features rather than a no-start. It nearly always traces to damaged wiring or a shorted connector.

Medium

Can I keep driving? Often yes, but a bus short can knock several body modules offline at once — expect warning lights and dead comfort features until it's repaired.

Common symptoms

What you'll notice

Multiple warning lights or a cluster acting erratically
Body and comfort features dead or intermittent (locks, windows, HVAC)
Several modules unreachable when scanned
A cluster of U-series communication codes stored together

Common causes

Most likely first

The two low-speed CAN wires shorted together from chafed or pinched insulationLikely
A crushed harness or connector where the (-) and (+) lines touchCommon
Water or corrosion bridging pins inside a connectorCommon
Damage from a prior repair, accident, or rodent chewingLess often
An internally failed module shorting the bus linesLess often

How to diagnose & fix

Work through it in order

Scan every module and note which ones dropped off — that isolates the affected bus branch.
Inspect the low-speed CAN harness and connectors for pinched, chafed, or wet spots.
With the key off, measure resistance between the bus (+) and (-) wires to confirm the short.
Unplug modules along that branch one at a time to find an internally shorted unit.
Repair the harness or connector, clear the code, and verify all modules communicate.

FAQ

Quick answers

Is it safe to drive with U0027?+

The engine usually still runs, but losing several body modules can disable safety warnings and features. Get it diagnosed promptly.

Can I just clear U0027?+

Clearing won't help — a hard short between the bus wires will set it again immediately until the wiring is fixed.

Related codes

Often seen with U0027

U0019Low Speed CAN Communication Bus U0022Low Speed CAN Communication Bus (+) Low U0023Low Speed CAN Communication Bus (+) High U0017Medium Speed CAN Communication Bus (-) Hig

Read & clear U0027 yourself

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

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