What it means
The two lines of differential bus A are shorted together. Communication impossible — both lines see the same voltage.
At a glance
- Usually lights the warning light of the system that lost communication
- The engine or gearbox may go into limp mode
How it works
Bus A uses separate positive and negative conductors to carry differential network signals between modules. U0036 indicates those two conductors are electrically connected to each other, preventing their signal levels from differing as intended and interrupting communication.
Common causes
Most likely first.
- CAN-H/CAN-L shorted together
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules and record event data, identifying which bus A nodes are offline and whether the fault appeared after wiring or component work.
- Inspect the bus A harness and connectors for crushed or melted sections, bent pins, conductive debris, or damage that could bridge the positive and negative wires.
- Check module power and grounds at nodes reporting no communication to rule out separate supply faults.
- With the vehicle powered down as specified by the manufacturer, test for continuity between the two bus A conductors and compare with service information.
- If the harness is not shorted, isolate connected modules and gateway connections according to the manufacturer's procedure to identify an internal node fault.
Common fixes
- Repair or replace a damaged harness section where the two bus A wires touch.
- Correct bent, contaminated, or damaged connector terminals bridging the conductors.
- Restore module power or ground if testing identifies a separate supply fault.
- Replace a module or repair gateway routing only if isolation testing confirms an internal short.
Can I keep driving?
The short can stop bus A communication and disable multiple functions or place modules in limp mode. Do not drive if essential controls or vehicle behavior are affected; arrange recovery if the vehicle cannot be operated safely.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.