U0033

Vehicle Communication Bus A (-) Open

Communication network (CAN bus) Generic OBD-II High

What it means

U0033 means the CAN "low" (-) wire of vehicle communication Bus A has an open (broken) circuit, so modules on that bus can no longer exchange data. How serious this is depends on what Bus A carries: if it's a body/comfort network you'll mostly see warning lights and dead features, but if it's the powertrain network the engine or transmission modules can drop offline and cause limp mode, stalling, or a no-start.

High

Can I keep driving? Depends on which bus is affected — an open communication line can knock several modules offline; if it's the powertrain network you may get limp mode, stalling, or a no-start, so treat it as urgent until diagnosed.

Common symptoms

What you'll notice

Multiple warning lights on at once and several modules reporting lost communication
Systems on this bus stop responding (could be powertrain, chassis, or body depending on the vehicle)
Possible reduced power, limp mode, or a no-start if the affected bus carries the engine/transmission modules
Gauges, displays, or accessories dead or erratic

Common causes

Most likely first

Break (open circuit) in the CAN-low (-) bus wireLikely
Corroded, backed-out, or disconnected connector pin on the busCommon
Failed splice or damaged harness sectionCommon
Missing bus termination resistor or a module that has lost its bus connection internallyLess often
Water intrusion or physical harness damageLess often

How to diagnose & fix

Work through it in order

Scan all modules and note which ones report lost communication — the group offline points to the open section of the bus.
Inspect Bus A wiring end to end for breaks, damaged connectors, and backed-out pins.
Measure continuity along the CAN-low (-) wire between modules to find the open.
Check the bus termination resistance (typically about 60 ohms across CAN-high/low) to confirm bus integrity.
Repair the open wire, splice, or connector, then clear and re-test communication.

FAQ

Quick answers

Is it safe to drive with U0033?+

Be cautious. An open bus wire can drop several modules offline at once. If the engine or transmission modules are on the affected bus you may lose power or fail to start, so get it diagnosed before relying on the car.

Can I just clear U0033?+

No lasting benefit — an open circuit is a physical fault, so the code returns immediately until the broken wire or connector is repaired.

Related codes

Often seen with U0033

U0030Vehicle Communication Bus A (+) Open U0031Vehicle Communication Bus A (+) Low U0032Vehicle Communication Bus A (+) High U0034Vehicle Communication Bus A (-) Low

Read & clear U0033 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