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Home / DTC / U0070 — Vehicle Communication Bus E (-) Low

U0070 — Vehicle Communication Bus E (-) Low

Detailed page for trouble code U0070.

34,332codes
59brands
11,841generic
22,491specific
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Code

U0070

Generic U — Network/User

Vehicle Communication Bus E (-) Low

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

Causes

  • Short to ground on the Bus E negative conductor
  • Damaged or chafed wiring harness or connector to Bus E
  • Failed CAN/LIN transceiver or module pulling the line low
  • Incorrect or missing bus termination (resistor)
  • Corroded or loose connector pins at control modules or splice points
  • Aftermarket device or module improperly connected to Bus E

Symptoms

  • Malfunction Indicator Lamp (MIL) or network warning lamp illuminated
  • Loss of communication with one or more modules on Bus E (erratic or no data on scanner)
  • Related systems inoperative or degraded (instrument cluster, body systems, drivability modules depending on bus purpose)
  • Intermittent operation of functions that use Bus E
  • Possible no-start or limp-home mode if critical module communication lost

What to check

  • Verify ignition on and record active and historic DTCs with a scan tool (note which modules report communication loss)
  • Check vehicle battery voltage and ground integrity before network testing (low battery can affect transceivers)
  • Visually inspect wiring harnesses, connectors and splices along the Bus E routing for damage, corrosion or pin/pushback
  • Check for aftermarket accessories tied into the bus and temporarily disconnect them
  • Measure voltage at the suspected module's Bus E negative pin against chassis ground with key on (use oscilloscope for dynamic checks if available)
  • Measure resistance across the bus termination (expected ~60 ohms when both terminations present in parallel; 120 ohms single termination)

Signal parameters

  • Nominal recessive voltage on CAN_H and CAN_L ≈ 2.5 V each (key on, no bus activity)
  • Dominant state typical: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
  • Expected differential voltage (active communication) ≈ 1.0–2.5 V depending on network
  • Termination: two 120 Ω resistors in parallel (≈ 60 Ω total) across CAN_H and CAN_L on a properly terminated bus
  • Indication of low Bus (-): CAN_L measured below ~1.0 V at rest or stuck near 0 V suggests a short to ground

Diagnostic algorithm

  1. Capture and record all network codes and freeze/frame data; note which modules are reporting and which are not responding.
  2. Verify battery voltage and engine/chassis grounds; poor ground can mimic low-line faults.
  3. Perform visual inspection along Bus E routing for damaged insulation, pinch points, repairs or aftermarket taps.
  4. With ignition ON, measure static voltage at CAN_L (Bus E negative) and CAN_H at multiple modules. Compare to nominal values (≈2.5 V recessive).
  5. Use an oscilloscope to observe CAN_H and CAN_L waveforms while commanding communication or cranking; look for CAN_L stuck low or abnormal waveforms.
  6. Measure resistance across CAN_H and CAN_L with the battery disconnected; expect ≈60 Ω for a properly terminated bus. If much lower, locate short/low impedance device.
  7. If a low impedance is present, isolate segments: disconnect modules (one at a time or at major junctions) to see when resistance/voltage returns to normal and identify faulty module or harness section.
  8. Inspect and clean connectors and pins at any module identified during isolation; repair or replace damaged connectors or wiring as needed.
  9. If a particular module's transceiver is suspected, substitute a known-good module (vehicle-specific procedure) or bench-test module transceiver per service manual before replacement.
  10. After repairs, clear codes and road/test to confirm the U0070 does not return and all modules communicate normally.

Likely causes

  • Wiring shorting to chassis ground at a harness rub point near body or frame
  • Failed transceiver in a control module on Bus E pulling CAN_L low
  • Corroded multi-pin connector or bent pin at a control module connector
  • Low-value splice or accessory tied into Bus E causing a partial short to ground

Fault status

⚠️ Status
Vehicle Communication Bus E (-) Low — the bus negative conductor voltage is below expected range (possible short to ground, failed transceiver, or wiring/connector fault).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1–3 hours

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Code

U0070

HYUNDAI U — Network/User

Vehicle Communication Bus E (-) Low

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

Causes

  • Short to ground on the Bus E negative conductor
  • Damaged or chafed wiring harness or connector to Bus E
  • Failed CAN/LIN transceiver or module pulling the line low
  • Incorrect or missing bus termination (resistor)
  • Corroded or loose connector pins at control modules or splice points
  • Aftermarket device or module improperly connected to Bus E

Symptoms

  • Malfunction Indicator Lamp (MIL) or network warning lamp illuminated
  • Loss of communication with one or more modules on Bus E (erratic or no data on scanner)
  • Related systems inoperative or degraded (instrument cluster, body systems, drivability modules depending on bus purpose)
  • Intermittent operation of functions that use Bus E
  • Possible no-start or limp-home mode if critical module communication lost

What to check

  • Verify ignition on and record active and historic DTCs with a scan tool (note which modules report communication loss)
  • Check vehicle battery voltage and ground integrity before network testing (low battery can affect transceivers)
  • Visually inspect wiring harnesses, connectors and splices along the Bus E routing for damage, corrosion or pin/pushback
  • Check for aftermarket accessories tied into the bus and temporarily disconnect them
  • Measure voltage at the suspected module's Bus E negative pin against chassis ground with key on (use oscilloscope for dynamic checks if available)
  • Measure resistance across the bus termination (expected ~60 ohms when both terminations present in parallel; 120 ohms single termination)

Signal parameters

  • Nominal recessive voltage on CAN_H and CAN_L ≈ 2.5 V each (key on, no bus activity)
  • Dominant state typical: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
  • Expected differential voltage (active communication) ≈ 1.0–2.5 V depending on network
  • Termination: two 120 Ω resistors in parallel (≈ 60 Ω total) across CAN_H and CAN_L on a properly terminated bus
  • Indication of low Bus (-): CAN_L measured below ~1.0 V at rest or stuck near 0 V suggests a short to ground

Diagnostic algorithm

  1. Capture and record all network codes and freeze/frame data; note which modules are reporting and which are not responding.
  2. Verify battery voltage and engine/chassis grounds; poor ground can mimic low-line faults.
  3. Perform visual inspection along Bus E routing for damaged insulation, pinch points, repairs or aftermarket taps.
  4. With ignition ON, measure static voltage at CAN_L (Bus E negative) and CAN_H at multiple modules. Compare to nominal values (≈2.5 V recessive).
  5. Use an oscilloscope to observe CAN_H and CAN_L waveforms while commanding communication or cranking; look for CAN_L stuck low or abnormal waveforms.
  6. Measure resistance across CAN_H and CAN_L with the battery disconnected; expect ≈60 Ω for a properly terminated bus. If much lower, locate short/low impedance device.
  7. If a low impedance is present, isolate segments: disconnect modules (one at a time or at major junctions) to see when resistance/voltage returns to normal and identify faulty module or harness section.
  8. Inspect and clean connectors and pins at any module identified during isolation; repair or replace damaged connectors or wiring as needed.
  9. If a particular module's transceiver is suspected, substitute a known-good module (vehicle-specific procedure) or bench-test module transceiver per service manual before replacement.
  10. After repairs, clear codes and road/test to confirm the U0070 does not return and all modules communicate normally.

Likely causes

  • Wiring shorting to chassis ground at a harness rub point near body or frame
  • Failed transceiver in a control module on Bus E pulling CAN_L low
  • Corroded multi-pin connector or bent pin at a control module connector
  • Low-value splice or accessory tied into Bus E causing a partial short to ground

Fault status

⚠️ Status
Vehicle Communication Bus E (-) Low — the bus negative conductor voltage is below expected range (possible short to ground, failed transceiver, or wiring/connector fault).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1–3 hours

Similar codes

U0073 U0100 U0101 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

U0070

MERCEDES-BENZ U — Network/User

Vehicle Communication Bus E (-) low

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

Causes

  • Short to ground on the Bus E negative conductor
  • Damaged or chafed wiring harness or connector to Bus E
  • Failed CAN/LIN transceiver or module pulling the line low
  • Incorrect or missing bus termination (resistor)
  • Corroded or loose connector pins at control modules or splice points
  • Aftermarket device or module improperly connected to Bus E

Symptoms

  • Malfunction Indicator Lamp (MIL) or network warning lamp illuminated
  • Loss of communication with one or more modules on Bus E (erratic or no data on scanner)
  • Related systems inoperative or degraded (instrument cluster, body systems, drivability modules depending on bus purpose)
  • Intermittent operation of functions that use Bus E
  • Possible no-start or limp-home mode if critical module communication lost

What to check

  • Verify ignition on and record active and historic DTCs with a scan tool (note which modules report communication loss)
  • Check vehicle battery voltage and ground integrity before network testing (low battery can affect transceivers)
  • Visually inspect wiring harnesses, connectors and splices along the Bus E routing for damage, corrosion or pin/pushback
  • Check for aftermarket accessories tied into the bus and temporarily disconnect them
  • Measure voltage at the suspected module's Bus E negative pin against chassis ground with key on (use oscilloscope for dynamic checks if available)
  • Measure resistance across the bus termination (expected ~60 ohms when both terminations present in parallel; 120 ohms single termination)

Signal parameters

  • Nominal recessive voltage on CAN_H and CAN_L ≈ 2.5 V each (key on, no bus activity)
  • Dominant state typical: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
  • Expected differential voltage (active communication) ≈ 1.0–2.5 V depending on network
  • Termination: two 120 Ω resistors in parallel (≈ 60 Ω total) across CAN_H and CAN_L on a properly terminated bus
  • Indication of low Bus (-): CAN_L measured below ~1.0 V at rest or stuck near 0 V suggests a short to ground

Diagnostic algorithm

  1. Capture and record all network codes and freeze/frame data; note which modules are reporting and which are not responding.
  2. Verify battery voltage and engine/chassis grounds; poor ground can mimic low-line faults.
  3. Perform visual inspection along Bus E routing for damaged insulation, pinch points, repairs or aftermarket taps.
  4. With ignition ON, measure static voltage at CAN_L (Bus E negative) and CAN_H at multiple modules. Compare to nominal values (≈2.5 V recessive).
  5. Use an oscilloscope to observe CAN_H and CAN_L waveforms while commanding communication or cranking; look for CAN_L stuck low or abnormal waveforms.
  6. Measure resistance across CAN_H and CAN_L with the battery disconnected; expect ≈60 Ω for a properly terminated bus. If much lower, locate short/low impedance device.
  7. If a low impedance is present, isolate segments: disconnect modules (one at a time or at major junctions) to see when resistance/voltage returns to normal and identify faulty module or harness section.
  8. Inspect and clean connectors and pins at any module identified during isolation; repair or replace damaged connectors or wiring as needed.
  9. If a particular module's transceiver is suspected, substitute a known-good module (vehicle-specific procedure) or bench-test module transceiver per service manual before replacement.
  10. After repairs, clear codes and road/test to confirm the U0070 does not return and all modules communicate normally.

Likely causes

  • Wiring shorting to chassis ground at a harness rub point near body or frame
  • Failed transceiver in a control module on Bus E pulling CAN_L low
  • Corroded multi-pin connector or bent pin at a control module connector
  • Low-value splice or accessory tied into Bus E causing a partial short to ground

Fault status

⚠️ Status
Vehicle Communication Bus E (-) Low — the bus negative conductor voltage is below expected range (possible short to ground, failed transceiver, or wiring/connector fault).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1–3 hours

Similar codes

U0073 U0100 U0101 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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