Code
U0074
Generic
U — Network/User
Control Module Communication Bus B Off
Views:
UK: 18
EN: 43
RU: 35
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring on Bus B (CAN high/low) or connector corrosion
- Failed CAN transceiver or communication module on Bus B
- Missing or failed termination resistor(s)
- Power or ground fault to a module on Bus B (including blown fuse)
- Gateway / network interface module failure or software fault
- Low battery or intermittent battery/charging system voltage
Symptoms
- Malfunction Indicator Lamp (MIL) or multiple warning lamps illuminated
- One or more modules not responding to scan tool or not showing data
- Loss of features controlled over Bus B (example: climate, body, infotainment, ABS/traction depending on vehicle)
- Intermittent or complete loss of instrument cluster messages
- Stored related U-codes and communication timeouts in scan data
What to check
- Verify the exact code and any related U-codes with a capable scan tool. Capture freeze frame and module list.
- Check vehicle battery voltage and charging system; ensure stable 12V (12.4–14.6 V with engine running).
- Visually inspect connectors, grounds, and harnesses for damage, corrosion, or disconnects on modules that use Bus B and the gateway.
- Check fuses and power/ground circuits for modules on Bus B.
- Measure resistance across CANH and CANL with ignition OFF; expected ~60 ohms (two 120 ohm terminators in parallel).
- Measure DC idle voltages: CANH and CANL should be near mid-supply (~2.5 V) with key on, engine off; CANH up to ~3.5 V and CANL down to ~1.5 V when dominant.
Signal parameters
- CAN idle (recessive) voltage: approximately 2.5 V on both CANH and CANL (key ON, engine OFF)
- CAN dominant voltages: CANH ~3.5 V, CANL ~1.5 V (vehicle dependent)
- Termination resistance: approx. 60 ohms measured across CANH–CANL (two 120 ohm terminators in parallel)
- Typical CAN data rates: commonly 250 kbps or 500 kbps on high-speed buses (verify vehicle spec)
- Expected: continuous periodic messages from gateway and multiple modules when bus is active
Diagnostic algorithm
- Connect a manufacturer-capable scan tool. Record U0074 and any accompanying U- or P-codes and module presence/absence. Note freeze frame data.
- Clear codes and see if U0074 returns. If intermittent, try key cycles and accessory on/off to reproduce.
- Verify battery voltage and inspect main power/ground points. Replace/repair low battery or bad grounds before further network work.
- Inspect wiring and connectors for the gateway and modules listed on Bus B. Repair any damaged connectors, pins, or harness chafing.
- Check fuses and power feeds to modules on Bus B; restore power where missing.
- With ignition ON, measure resistance across CANH–CANL (expect ~60 ohms). If open or very high, locate open circuit by disconnecting branch connectors and rechecking.
- Measure voltages at CANH and CANL with key ON. If short to battery or ground is suspected, isolate sections by disconnecting modules one at a time and rechecking bus status.
- Use an oscilloscope to view waveforms. Look for correct recessive/dominant levels, reflections, or noise. A flat line or saturated level indicates a short or failed transceiver.
- If isolating a failed module, confirm by substituting a known good module (when available and permitted) or replacing suspected module or transceiver.
- If wiring and modules test OK but communication remains off, inspect/replace gateway or network interface module and verify software/calibration levels. Relearn procedures or module programming may be required.
- After repair, clear codes, verify all previously missing modules appear on the scan tool, and perform a road/operation test to confirm normal network operation and that U0074 does not return.
Likely causes
- Loose/disconnected connector at a module on Bus B (common point or gateway)
- Damaged wiring harness (pinched, chafed) causing CANH/CANL short or open
- Failed CAN transceiver in a control module (gateway, BCM, ECU on Bus B)
- Removed or failed termination resistor or incorrect termination after repair
- Blown fuse or lost power/ground to the gateway or main module on Bus B
Fault status
Status
Control Module Communication Bus B Off — No communication detected on the vehicle's Bus B network. Modules on that bus are not responding.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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Code
U0074
HYUNDAI
U — Network/User
Control Module Communication Bus “B” Off
Views:
UK: 13
EN: 21
RU: 18
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring on Bus B (CAN high/low) or connector corrosion
- Failed CAN transceiver or communication module on Bus B
- Missing or failed termination resistor(s)
- Power or ground fault to a module on Bus B (including blown fuse)
- Gateway / network interface module failure or software fault
- Low battery or intermittent battery/charging system voltage
Symptoms
- Malfunction Indicator Lamp (MIL) or multiple warning lamps illuminated
- One or more modules not responding to scan tool or not showing data
- Loss of features controlled over Bus B (example: climate, body, infotainment, ABS/traction depending on vehicle)
- Intermittent or complete loss of instrument cluster messages
- Stored related U-codes and communication timeouts in scan data
What to check
- Verify the exact code and any related U-codes with a capable scan tool. Capture freeze frame and module list.
- Check vehicle battery voltage and charging system; ensure stable 12V (12.4–14.6 V with engine running).
- Visually inspect connectors, grounds, and harnesses for damage, corrosion, or disconnects on modules that use Bus B and the gateway.
- Check fuses and power/ground circuits for modules on Bus B.
- Measure resistance across CANH and CANL with ignition OFF; expected ~60 ohms (two 120 ohm terminators in parallel).
- Measure DC idle voltages: CANH and CANL should be near mid-supply (~2.5 V) with key on, engine off; CANH up to ~3.5 V and CANL down to ~1.5 V when dominant.
Signal parameters
- CAN idle (recessive) voltage: approximately 2.5 V on both CANH and CANL (key ON, engine OFF)
- CAN dominant voltages: CANH ~3.5 V, CANL ~1.5 V (vehicle dependent)
- Termination resistance: approx. 60 ohms measured across CANH–CANL (two 120 ohm terminators in parallel)
- Typical CAN data rates: commonly 250 kbps or 500 kbps on high-speed buses (verify vehicle spec)
- Expected: continuous periodic messages from gateway and multiple modules when bus is active
Diagnostic algorithm
- Connect a manufacturer-capable scan tool. Record U0074 and any accompanying U- or P-codes and module presence/absence. Note freeze frame data.
- Clear codes and see if U0074 returns. If intermittent, try key cycles and accessory on/off to reproduce.
- Verify battery voltage and inspect main power/ground points. Replace/repair low battery or bad grounds before further network work.
- Inspect wiring and connectors for the gateway and modules listed on Bus B. Repair any damaged connectors, pins, or harness chafing.
- Check fuses and power feeds to modules on Bus B; restore power where missing.
- With ignition ON, measure resistance across CANH–CANL (expect ~60 ohms). If open or very high, locate open circuit by disconnecting branch connectors and rechecking.
- Measure voltages at CANH and CANL with key ON. If short to battery or ground is suspected, isolate sections by disconnecting modules one at a time and rechecking bus status.
- Use an oscilloscope to view waveforms. Look for correct recessive/dominant levels, reflections, or noise. A flat line or saturated level indicates a short or failed transceiver.
- If isolating a failed module, confirm by substituting a known good module (when available and permitted) or replacing suspected module or transceiver.
- If wiring and modules test OK but communication remains off, inspect/replace gateway or network interface module and verify software/calibration levels. Relearn procedures or module programming may be required.
- After repair, clear codes, verify all previously missing modules appear on the scan tool, and perform a road/operation test to confirm normal network operation and that U0074 does not return.
Likely causes
- Loose/disconnected connector at a module on Bus B (common point or gateway)
- Damaged wiring harness (pinched, chafed) causing CANH/CANL short or open
- Failed CAN transceiver in a control module (gateway, BCM, ECU on Bus B)
- Removed or failed termination resistor or incorrect termination after repair
- Blown fuse or lost power/ground to the gateway or main module on Bus B
Fault status
Status
Control Module Communication Bus B Off — No communication detected on the vehicle's Bus B network. Modules on that bus are not responding.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
Similar codes
Your experience will help others
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Was this AI description helpful?
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👍 Like
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Code
U0074
LAND ROVER
U — Network/User
Communication bus of control module B deactivated
Views:
UK: 5
EN: 10
RU: 9
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring on Bus B (CAN high/low) or connector corrosion
- Failed CAN transceiver or communication module on Bus B
- Missing or failed termination resistor(s)
- Power or ground fault to a module on Bus B (including blown fuse)
- Gateway / network interface module failure or software fault
- Low battery or intermittent battery/charging system voltage
Symptoms
- Malfunction Indicator Lamp (MIL) or multiple warning lamps illuminated
- One or more modules not responding to scan tool or not showing data
- Loss of features controlled over Bus B (example: climate, body, infotainment, ABS/traction depending on vehicle)
- Intermittent or complete loss of instrument cluster messages
- Stored related U-codes and communication timeouts in scan data
What to check
- Verify the exact code and any related U-codes with a capable scan tool. Capture freeze frame and module list.
- Check vehicle battery voltage and charging system; ensure stable 12V (12.4–14.6 V with engine running).
- Visually inspect connectors, grounds, and harnesses for damage, corrosion, or disconnects on modules that use Bus B and the gateway.
- Check fuses and power/ground circuits for modules on Bus B.
- Measure resistance across CANH and CANL with ignition OFF; expected ~60 ohms (two 120 ohm terminators in parallel).
- Measure DC idle voltages: CANH and CANL should be near mid-supply (~2.5 V) with key on, engine off; CANH up to ~3.5 V and CANL down to ~1.5 V when dominant.
Signal parameters
- CAN idle (recessive) voltage: approximately 2.5 V on both CANH and CANL (key ON, engine OFF)
- CAN dominant voltages: CANH ~3.5 V, CANL ~1.5 V (vehicle dependent)
- Termination resistance: approx. 60 ohms measured across CANH–CANL (two 120 ohm terminators in parallel)
- Typical CAN data rates: commonly 250 kbps or 500 kbps on high-speed buses (verify vehicle spec)
- Expected: continuous periodic messages from gateway and multiple modules when bus is active
Diagnostic algorithm
- Connect a manufacturer-capable scan tool. Record U0074 and any accompanying U- or P-codes and module presence/absence. Note freeze frame data.
- Clear codes and see if U0074 returns. If intermittent, try key cycles and accessory on/off to reproduce.
- Verify battery voltage and inspect main power/ground points. Replace/repair low battery or bad grounds before further network work.
- Inspect wiring and connectors for the gateway and modules listed on Bus B. Repair any damaged connectors, pins, or harness chafing.
- Check fuses and power feeds to modules on Bus B; restore power where missing.
- With ignition ON, measure resistance across CANH–CANL (expect ~60 ohms). If open or very high, locate open circuit by disconnecting branch connectors and rechecking.
- Measure voltages at CANH and CANL with key ON. If short to battery or ground is suspected, isolate sections by disconnecting modules one at a time and rechecking bus status.
- Use an oscilloscope to view waveforms. Look for correct recessive/dominant levels, reflections, or noise. A flat line or saturated level indicates a short or failed transceiver.
- If isolating a failed module, confirm by substituting a known good module (when available and permitted) or replacing suspected module or transceiver.
- If wiring and modules test OK but communication remains off, inspect/replace gateway or network interface module and verify software/calibration levels. Relearn procedures or module programming may be required.
- After repair, clear codes, verify all previously missing modules appear on the scan tool, and perform a road/operation test to confirm normal network operation and that U0074 does not return.
Likely causes
- Loose/disconnected connector at a module on Bus B (common point or gateway)
- Damaged wiring harness (pinched, chafed) causing CANH/CANL short or open
- Failed CAN transceiver in a control module (gateway, BCM, ECU on Bus B)
- Removed or failed termination resistor or incorrect termination after repair
- Blown fuse or lost power/ground to the gateway or main module on Bus B
Fault status
Status
Control Module Communication Bus B Off — No communication detected on the vehicle's Bus B network. Modules on that bus are not responding.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
Similar codes
Workshop Manuals
Repair manuals for LAND ROVER
3
Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop ManualLand Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
Workshop ManualLand Rover Range Rover — Electrical Library (LRL 0453ENG, 2002)
Workshop ManualYour experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email