U0012 — Medium Speed CAN Communication Bus (+) Open

OBD2 code U0012 flags a problem with the vehicle network (CAN bus) communication (medium speed CAN communication bus (+) open). Short, gentle driving to a shop is usually possible. Common culprits: water ingress in harness junctions, poor grounds or low battery voltage, corroded connectors, especially in wet areas.

vehicle network

Is it safe to drive?

Drive with caution Depends on what is affected. A single dead convenience module is fine to drive with; loss of communication with engine, braking or steering modules is not. If multiple critical systems drop out, do not drive.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm U0012 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many U0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the vehicle network (CAN bus) communication for damage, corrosion, chafing or poor contact.
Subsystem check Measure resistance between CAN-High and CAN-Low at the OBD port with power off — about 60 Ω is healthy.
Subsystem check Scan all modules: the one that does not respond is either the culprit or downstream of the break.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm U0012 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for U0012 (parts and labor, USD, independent shop rates): Remove interfering aftermarket device: $0–$150; Repair CAN wiring or connectors: $100–$400; Replace the faulty control module: $300–$1,500. Overall, fixing U0012 usually costs between $0 and $1,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

Is it safe to drive with U0012?

Depends on what is affected. A single dead convenience module is fine to drive with; loss of communication with engine, braking or steering modules is not. If multiple critical systems drop out, do not drive.

What are the symptoms of U0012?

Drivers most often notice: intermittent loss of functions (gauges, windows, steering assist), no-start or intermittent starting in some cases, modules intermittently not communicating with the scanner, multiple warning lights on at once.

What is the most common cause of U0012?

The most common causes are: water ingress in harness junctions, poor grounds or low battery voltage, corroded connectors, especially in wet areas.

How do I diagnose U0012 myself?

Start with a scan: confirm U0012, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the vehicle network (CAN bus) communication, and verify the suspect component against live data before buying parts.

What does OBD2 code U0012 mean?

What does U0012 mean?

When U0012 appears on a scan, it means the control module has flagged a problem in the vehicle network (CAN bus) communication: medium speed CAN communication bus (+) open. The fault sits in the vehicle network group of the OBD2 standard.

To set U0012, the control module compares live readings of the vehicle network (CAN bus) communication against calibrated limits, usually over several drive cycles. Alongside the code it stores a freeze frame — a snapshot of rpm, load, coolant temperature and vehicle speed at the moment of failure. Reading that snapshot first saves diagnostic time.

Common symptoms of U0012

intermittent loss of functions (gauges, windows, steering assist)
no-start or intermittent starting in some cases
modules intermittently not communicating with the scanner
multiple warning lights on at once
random, hard-to-reproduce electrical glitches

What causes U0012?

aftermarket equipment interfering with the bus
a faulty module pulling the bus down
poor grounds or low battery voltage
damaged CAN bus wiring or short to power/ground
water ingress in harness junctions

How to diagnose U0012

Connect an OBD2 scanner, confirm U0012 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many U0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Visually inspect the wiring harness and connectors related to the vehicle network (CAN bus) communication for damage, corrosion, chafing or poor contact.
Measure resistance between CAN-High and CAN-Low at the OBD port with power off — about 60 Ω is healthy.
Scan all modules: the one that does not respond is either the culprit or downstream of the break.
Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm U0012 does not return.

How to fix U0012

Start with the cheapest and most common causes before replacing expensive parts:

Remove interfering aftermarket device — $0–$150
Repair CAN wiring or connectors — $100–$400
Replace the faulty control module — $300–$1,500

How much does it cost to fix U0012?

Repair cost depends on which component actually failed. Typical scenarios for U0012 (parts and labor, USD, independent shop rates):

Remove interfering aftermarket device: $0–$150
Repair CAN wiring or connectors: $100–$400
Replace the faulty control module: $300–$1,500

Overall, fixing U0012 usually costs between $0 and $1,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.