Code
P1672
DAEWOO
P — Powertrain
Can comm flt(can bus off)
Views:
UK: 6
EN: 9
RU: 5
AI status
Completed
Completed
100%
Causes
- Short or open in CAN_H or CAN_L wiring
- Failed CAN transceiver or control module (ECU/BCM/gateway)
- Incorrect or missing termination resistors
- Corroded/damaged connectors or ground/battery connections
- Aftermarket device (alarm/radio) interfering with CAN bus
- Intermittent wiring fault (chafing, water ingress)
Symptoms
- Malfunction Indicator Lamp (MIL) or CAN fault lamp on
- Loss of communication with one or multiple control modules on scan tool
- Multiple unrelated warning lights (ABS, airbag, instrument cluster)
- No crank/no start or intermittent cranking problems if ECM/PCM is offline
- Unresponsive multifunction systems (windows, instruments, HVAC)
- Intermittent or permanent faults that clear when connectors are unplugged/plugged
What to check
- Connect a diagnostic scan tool and confirm P1672 and any other U-codes or communication faults
- Check for CAN bus off status and note which modules are not responding
- Visually inspect CAN wiring harnesses, connectors, and ground points for damage or corrosion
- Measure termination resistance between CAN_H and CAN_L with ignition off (expect ~60 Ω with two 120 Ω terminators)
- Measure idle voltages of CAN_H and CAN_L with ignition ON and engine off (expect ~2.5 V on each, differential ~0 V)
- Check CAN_H and CAN_L for shorts to battery voltage and to ground (infinite/very high resistance expected to battery/ground)
Signal parameters
- CAN_H idle voltage ≈ 2.5 V (recessive)
- CAN_L idle voltage ≈ 2.5 V (recessive)
- Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (during data)
- Differential voltage (CAN_H − CAN_L) ≈ 0 V when idle; peak ±2 V during bits
- Bus termination resistance ≈ 60 Ω (two 120 Ω terminators in parallel)
Diagnostic algorithm
- Record all stored DTCs and freeze frame data with a capable scan tool; note which modules do not respond
- Attempt to clear codes and re-scan to see if code returns or if bus comes back, documenting any repeat behavior
- Visually inspect harness routing and connectors at gateway, BCM, ECM, and other non-responding modules; repair or reseat any corroded/damaged connectors
- Measure resistance between CAN_H and CAN_L with ignition off; if not ~60 Ω, inspect/replace missing or damaged terminators
- With ignition on, measure voltages at a known good connector: verify both CAN lines sit near 2.5 V; if one line is low/high, trace that line for short to ground or battery
- Isolate segments: disconnect modules one at a time (begin with non-critical modules) to see when bus returns; this helps identify a module holding the bus dominant
- If a single module is identified as faulty, verify power and ground to that module before replacement; replace or reprogram module only after confirming it’s the fault
- After repairs, clear codes and verify normal communication with scan tool and that CAN voltage/termination readings are within spec
- If wiring and terminations are good but fault persists, consider replacing or reflashing the network gateway or affected control module
Likely causes
- CAN_H or CAN_L shorted to battery or ground
- Broken/damaged CAN wire between major modules (ECM, BCM, gateway)
- Failed module with stuck dominant driver (holding bus low/high)
- Missing or failed 120 Ω termination(s) leading to wrong bus impedance
- Corroded connector at a common splice or gateway module
Fault status
Status
Controller detected CAN bus-off condition (network communication lost or held in dominant state).
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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