U0036

Code

Generic U — Network/User

Vehicle Communication Bus A (-) shorted to Bus A (+)

Brand: Generic

Type: U — Network/User

Views: UK: 25 EN: 43 RU: 23

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Page language: EN

Causes

Damaged wiring harness with CAN_L and CAN_H conductor contact
Corroded or water-intruded connector causing internal short
Failed CAN transceiver (inside a module) shorting CAN_L to CAN_H
Aftermarket accessory improperly tied into the CAN bus
Incorrect or damaged termination resistors (open, shorted, or wrong value)
Physical damage at a splice, junction block or body harness abrasion

Symptoms

Malfunction Indicator Lamp (MIL) or DTC lamp illuminated
Multiple modules on Bus A show ‘no communication’ or erroneous messages
Intermittent or no-start if key modules are on Bus A
Loss of functions controlled over Bus A (instrument cluster, ABS, transmission, etc.)
Erratic module behavior, frozen gauges, or failure of features tied to the network

What to check

Scan vehicle with a professional scan tool; record all U-codes and modules reporting on Bus A
Visually inspect CAN wiring, connectors, and splices along the Bus A route for damage, corrosion, or water intrusion
Check connectors at modules on Bus A; unplug/replug to reveal intermittent faults (perform with ignition off as manufacturer recommends)
Measure resistance between CAN_H and CAN_L (ignition off). With both termination resistors present expect about 60 ohms end-to-end (two 120 Ω in parallel)
Check for shorts to battery voltage and ground: measure continuity from CAN_H and CAN_L to vehicle battery positive and chassis ground
Use a lab scope or CAN bus analyzer to view waveforms on CAN_H and CAN_L while cranking/idle; look for stuck dominant level or identical voltages on both wires

Signal parameters

Normal (recessive): CAN_H ≈ 2.5V, CAN_L ≈ 2.5V (both equal)
Normal (dominant): CAN_H ≈ 3.5V, CAN_L ≈ 1.5V (approx. 2V differential)
Expected bus differential: ~2.0V when dominant; ~0V when recessive
Fault symptom for short CAN_L to CAN_H: CAN_H and CAN_L may read nearly the same voltage, bus stuck dominant or no valid differential waveform, abnormal voltages to battery or ground

Diagnostic algorithm

Connect a scan tool; record all codes and note which modules are present on Vehicle Communication Bus A.
Perform a visual inspection of the Bus A harness, connectors, junctions and any recent repair or aftermarket installation areas for damage, pins pushed out, corrosion or moisture.
With ignition off, measure DC resistance between CAN_H and CAN_L at a known good junction—expect approximately 60 Ω (two 120 Ω terminators in parallel). Significant deviation indicates open or incorrect termination.
Check continuity from each CAN conductor to chassis ground and to battery positive to detect unintended shorts to power/ground.
With ignition on and engine off, monitor CAN_H and CAN_L with a scope or CAN analyzer. Look for valid recessive/dominant waveforms and a ~2V differential. If both lines are identical or waveform is absent, there is a short or failed transceiver.
To isolate the fault, disconnect modules or harness branches on Bus A one at a time while watching the scan tool and waveforms; when the fault clears after unplugging a module or branch, suspect that module or harness segment.
Inspect and test suspected module transceiver power, ground, and internal short to the other CAN conductor. Replace or repair as required.
Repair damaged wiring, connectors, or replace failed modules. Verify correct 120 Ω termination at each end of the bus and proper wiring routing away from high-voltage sources.
Clear codes and perform a full network verification by re-scanning and road-testing to ensure the communication fault does not return.

Likely causes

Physical short where CAN_L and CAN_H are pinched or chafed together
Faulty module transceiver on Bus A creating an internal short
Connector contamination (water, corrosion) grounding or shorting signal conductors
Incorrect wiring from a repair or aftermarket installation