Chafed or damaged wiring harness where CAN High and CAN Low wires run close together, allowing the conductors to touch; Water intrusion into a connector or module, causing corrosion that bridges the two data lines; A faulty control module with an internal short between its CAN pins; Aftermarket accessories improperly tapped into the bus wiring, creating a short; Pinched wiring during previous repairs or accident damage; Failed transmission range sensor or other sensor internally shorting the bus

DTC codes / U00xx · Network wiring and bus faults / U0036

U0036Vehicle Communication Bus A (shorted to Bus A)

Q: What does code U0036 mean?

Vehicle Communication Bus A (shorted to Bus A). U0036 is a generic network communication code indicating that the vehicle's main communication bus, typically the high-speed CAN (Controller Area Network) bus, has a short circuit between its two data lines, CAN High and CAN Low. The computer detected an abnormal voltage condition where the two bus wires are electrically connected, preventing normal differential signaling and disrupting communication between control modules.

U0036 is a generic network communication code indicating that the vehicle's main communication bus, typically the high-speed CAN (Controller Area Network) bus, has a short circuit between its two data lines, CAN High and CAN Low. The computer detected an abnormal voltage condition where the two bus wires are electrically connected, preventing normal differential signaling and disrupting communication between control modules.

SystemNetwork

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaNetwork wiring and bus faults

Symptoms you may notice

Multiple warning lights illuminated on the dashboard, often including the check engine light, ABS, and airbag lights
The engine may crank but not start, or may start and run poorly due to lost communication with the engine control module
Transmission may default to limp mode or fail to shift properly
Inoperative accessories such as the radio, climate control, or power windows
Often no symptoms besides the warning light if the short is intermittent or affects only non-critical modules
Intermittent electrical glitches, such as flickering lights or random module resets

Common causes, most likely first

Chafed or damaged wiring harness where CAN High and CAN Low wires run close together, allowing the conductors to touch
Water intrusion into a connector or module, causing corrosion that bridges the two data lines
A faulty control module with an internal short between its CAN pins
Aftermarket accessories improperly tapped into the bus wiring, creating a short
Pinched wiring during previous repairs or accident damage
Failed transmission range sensor or other sensor internally shorting the bus

How to diagnose and fix it

Perform a visual inspection of the CAN bus wiring for obvious damage, chafing, or corrosion, especially near connectors and known rub points
Use a digital multimeter to measure resistance between CAN High and CAN Low at the diagnostic link connector (DLC); a reading near 0 ohms indicates a short
Disconnect modules one by one to isolate the short; when the resistance returns to normal (about 60 ohms), the last disconnected module or its wiring is the culprit
Inspect and clean any suspect connectors for water intrusion or corrosion, and repair or replace damaged pins
Repair or replace the section of wiring harness where the short is found, using proper soldering and heat-shrink techniques
If a module is found to be internally shorted, replace or reprogram it as required
Clear the code and verify communication is restored across all modules with a scan tool

Don't Replace Modules Before Checking These

A common oversight is assuming the code points to a failed module, but the short is often in the wiring harness where it rubs against a metal bracket or passes through a tight grommet.
Water intrusion into a connector, especially in areas prone to leaks like the cowl or trunk, can create a conductive path between CAN High and CAN Low that only appears when wet.
Aftermarket installations such as alarm systems, remote starters, or dash cams are frequent culprits because installers may inadvertently pinch or pierce the bus wires.
The code can be set by a short in a non-critical module, so the vehicle may still run and drive, but communication with that module is lost, affecting features like climate control or infotainment.
Resistance testing at the DLC is a quick first step, but a shorted module can pull the entire bus down, so disconnecting modules one at a time is the most reliable isolation method.

Can I keep driving with U0036?

If the vehicle starts and runs, it may be safe to drive a short distance to a repair shop, but avoid highway driving or long trips because the fault can cause unpredictable module failures and loss of critical systems like ABS or power steering. If the engine does not start or the vehicle is in limp mode, have it towed to prevent further damage or unsafe operation.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.