B1548
CAN No communication
Causes
- Open or shorted CAN bus wiring (CAN High or CAN Low)
- Failed or powered-down control module on the bus
- Missing or failed termination resistor(s) on the CAN bus
- Blown fuse or loss of power/ground to one or more modules
- Corroded or loose connectors, broken pins at modules or junctions
- Aftermarket electronic device interfering with the bus (alarm, radio, tracker)
Symptoms
- One or more control modules not responding to scan tool (no communication)
- Multiple dashboard warning lamps illuminated or intermittent instrument cluster operation
- Loss of functions tied to affected modules (ABS, SRS lights, HVAC, gauges, immobilizer)
- Intermittent or permanent failure of networked systems
- Diagnostic trouble codes stored for multiple modules or U-codes indicating lost communication
What to check
- Use a capable scan tool to read stored DTCs from all modules and note any U-codes
- Visually inspect all CAN-related fuses and relays; confirm battery voltage and good chassis/engine ground
- Inspect wiring harnesses, connectors and junction blocks for corrosion, bent pins, breaks, or water intrusion near the instrument panel and BCM
- Measure CAN termination resistance between CAN High and CAN Low at a convenient connector (should be ~60 ohms with ignition off)
- Check for back-probed voltages on CAN High and CAN Low with ignition ON (see signal_params)
- Disconnect/remove any recently installed aftermarket devices connected to the vehicle network
Signal parameters
- CAN idle voltage (to battery ground): CAN High ≈ 2.5 V, CAN Low ≈ 2.5 V (both center at ~2.5V)
- Dominant/Active voltages during data: CAN High ≈ 3.5 V, CAN Low ≈ 1.5 V (voltage difference present)
- Termination resistance across CAN H and CAN L: approx. 60 ohms (two 120 Ω terminators in parallel)
- Short to battery/ground will show CAN lines pulled toward 12 V or 0 V respectively
- Bus activity: valid periodic CAN traffic visible on a scope or CAN monitor at expected bitrate (commonly 250 kb/s or 500 kb/s on vehicle networks)
Diagnostic algorithm
- Connect a diagnostic scan tool and record all modules’ DTCs and network status (note any U-codes).
- Verify battery voltage is stable (12.4–12.8 V) and check main power/ground circuits to suspected modules.
- Inspect and test CAN bus fuses and relays; replace any blown fuses and retest communication.
- Visually inspect connectors and harnesses along the CAN backbone (instrument panel, BCM, junction boxes). Repair any damaged wiring or corroded pins.
- Measure termination resistance across CAN H and CAN L at a known good connector; if not ≈60 Ω, locate missing/bad terminator or open circuit.
- With ignition ON, measure CAN High and CAN Low voltages at the affected module(s). Compare to expected idle voltages (~2.5 V).
- If voltages are abnormal, isolate the fault by disconnecting modules one at a time (start at ends of the bus) and observe when communications return to identify the offending segment or module.
- Use an oscilloscope or CAN bus analyzer to confirm packet traffic and to identify noise, stuck dominant states, or low amplitude signals.
- If a module is found to be unresponsive but wiring and bus integrity are good, follow manufacturer procedure for module reset or replacement; reprogram or reinitialize as required.
- After repair, clear DTCs, verify all modules respond, and perform a road test or network exercise to confirm stability.
Likely causes
- Blown CAN fuse or loss of ground to the affected module
- Damaged/shorted CAN High or CAN Low wiring near BCM or junction connectors
- Detached or corroded connector at the affected control module
- Failed instrument cluster/BCM preventing bus communications
- Incorrect aftermarket device wiring connected to CAN lines
Fault status
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Manual library for MITSUBISHI
Browse 406 MITSUBISHI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.
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MITSUBISHI: 2021
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MITSUBISHI: 2020
B1548
Power Window Master Circuit Open
Causes
- Open or shorted CAN bus wiring (CAN High or CAN Low)
- Failed or powered-down control module on the bus
- Missing or failed termination resistor(s) on the CAN bus
- Blown fuse or loss of power/ground to one or more modules
- Corroded or loose connectors, broken pins at modules or junctions
- Aftermarket electronic device interfering with the bus (alarm, radio, tracker)
Symptoms
- One or more control modules not responding to scan tool (no communication)
- Multiple dashboard warning lamps illuminated or intermittent instrument cluster operation
- Loss of functions tied to affected modules (ABS, SRS lights, HVAC, gauges, immobilizer)
- Intermittent or permanent failure of networked systems
- Diagnostic trouble codes stored for multiple modules or U-codes indicating lost communication
What to check
- Use a capable scan tool to read stored DTCs from all modules and note any U-codes
- Visually inspect all CAN-related fuses and relays; confirm battery voltage and good chassis/engine ground
- Inspect wiring harnesses, connectors and junction blocks for corrosion, bent pins, breaks, or water intrusion near the instrument panel and BCM
- Measure CAN termination resistance between CAN High and CAN Low at a convenient connector (should be ~60 ohms with ignition off)
- Check for back-probed voltages on CAN High and CAN Low with ignition ON (see signal_params)
- Disconnect/remove any recently installed aftermarket devices connected to the vehicle network
Signal parameters
- CAN idle voltage (to battery ground): CAN High ≈ 2.5 V, CAN Low ≈ 2.5 V (both center at ~2.5V)
- Dominant/Active voltages during data: CAN High ≈ 3.5 V, CAN Low ≈ 1.5 V (voltage difference present)
- Termination resistance across CAN H and CAN L: approx. 60 ohms (two 120 Ω terminators in parallel)
- Short to battery/ground will show CAN lines pulled toward 12 V or 0 V respectively
- Bus activity: valid periodic CAN traffic visible on a scope or CAN monitor at expected bitrate (commonly 250 kb/s or 500 kb/s on vehicle networks)
Diagnostic algorithm
- Connect a diagnostic scan tool and record all modules’ DTCs and network status (note any U-codes).
- Verify battery voltage is stable (12.4–12.8 V) and check main power/ground circuits to suspected modules.
- Inspect and test CAN bus fuses and relays; replace any blown fuses and retest communication.
- Visually inspect connectors and harnesses along the CAN backbone (instrument panel, BCM, junction boxes). Repair any damaged wiring or corroded pins.
- Measure termination resistance across CAN H and CAN L at a known good connector; if not ≈60 Ω, locate missing/bad terminator or open circuit.
- With ignition ON, measure CAN High and CAN Low voltages at the affected module(s). Compare to expected idle voltages (~2.5 V).
- If voltages are abnormal, isolate the fault by disconnecting modules one at a time (start at ends of the bus) and observe when communications return to identify the offending segment or module.
- Use an oscilloscope or CAN bus analyzer to confirm packet traffic and to identify noise, stuck dominant states, or low amplitude signals.
- If a module is found to be unresponsive but wiring and bus integrity are good, follow manufacturer procedure for module reset or replacement; reprogram or reinitialize as required.
- After repair, clear DTCs, verify all modules respond, and perform a road test or network exercise to confirm stability.
Likely causes
- Blown CAN fuse or loss of ground to the affected module
- Damaged/shorted CAN High or CAN Low wiring near BCM or junction connectors
- Detached or corroded connector at the affected control module
- Failed instrument cluster/BCM preventing bus communications
- Incorrect aftermarket device wiring connected to CAN lines
Fault status
Similar codes
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