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Home / DTC / U0036 — Vehicle Communication Bus A (-) shorted to Bus A (+)

U0036 — Vehicle Communication Bus A (-) shorted to Bus A (+)

Detailed page for trouble code U0036.

35,619codes
59brands
11,925generic
23,694specific
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Code

U0036

Generic U — Network/User

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

Brand: Generic
Type: U — Network/User
AI status
Completed
ready
Completed 100%
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

  1. Connect a scan tool; record all codes and note which modules are present on Vehicle Communication Bus A.
  2. 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.
  3. 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.
  4. Check continuity from each CAN conductor to chassis ground and to battery positive to detect unintended shorts to power/ground.
  5. 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.
  6. 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.
  7. Inspect and test suspected module transceiver power, ground, and internal short to the other CAN conductor. Replace or repair as required.
  8. 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.
  9. 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

Fault status

⚠️ Status
Bus A (-) (CAN_L) shorted to Bus A (+) (CAN_H) — CAN Bus A communication fault detected.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-4 hours

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Code

U0036

HYUNDAI U — Network/User

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

Brand: HYUNDAI
Type: U — Network/User
AI status
Completed
ready
Completed 100%
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

  1. Connect a scan tool; record all codes and note which modules are present on Vehicle Communication Bus A.
  2. 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.
  3. 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.
  4. Check continuity from each CAN conductor to chassis ground and to battery positive to detect unintended shorts to power/ground.
  5. 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.
  6. 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.
  7. Inspect and test suspected module transceiver power, ground, and internal short to the other CAN conductor. Replace or repair as required.
  8. 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.
  9. 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

Fault status

⚠️ Status
Bus A (-) (CAN_L) shorted to Bus A (+) (CAN_H) — CAN Bus A communication fault detected.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-4 hours

Similar codes

U0035 U0001 U0073 U0100 U0140 U0121
371

Browse 371 HYUNDAI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

HYUNDAI

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
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Code

U0036

MERCEDES-BENZ U — Network/User

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

Brand: MERCEDES-BENZ
Type: U — Network/User
AI status
Completed
ready
Completed 100%
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

  1. Connect a scan tool; record all codes and note which modules are present on Vehicle Communication Bus A.
  2. 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.
  3. 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.
  4. Check continuity from each CAN conductor to chassis ground and to battery positive to detect unintended shorts to power/ground.
  5. 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.
  6. 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.
  7. Inspect and test suspected module transceiver power, ground, and internal short to the other CAN conductor. Replace or repair as required.
  8. 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.
  9. 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

Fault status

⚠️ Status
Bus A (-) (CAN_L) shorted to Bus A (+) (CAN_H) — CAN Bus A communication fault detected.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-4 hours

Similar codes

U0035 U0001 U0073 U0100 U0140 U0121
856

Browse 856 MERCEDES-BENZ manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

MERCEDES-BENZ

Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

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