P5000 — Communication malfunction between ECM and other computers (CAN)

Causes

• Open or shorted CAN High (CAN H) or CAN Low (CAN L) wiring
• Corroded or loose connectors or pin damage at modules or junctions
• Missing or failed termination resistor(s)
• Failed or powered-off module (ECM or other node) driving the bus to error state
• Low system voltage, weak battery, or poor ground
• Water intrusion or contamination in connectors or junction boxes

Symptoms

• Multiple communication-related DTCs or module errors (U-codes visible)
• Loss or intermittent loss of functions controlled by other modules (ABS, instrument cluster, transmission, etc.)
• Warning lights on dash (check engine, ABS, traction control, etc.)
• Intermittent starts, limp-home mode, or degraded operation of systems
• Modules show 'no communication' or 'bus off' on diagnostic tool

What to check

• Read stored and pending DTCs from all control modules; record U- and P-codes
• Check battery voltage and charging system (voltage should be stable ~12.4–14.4 V while cranking/idle)
• Visual inspection of CAN wiring harnesses, connectors, and junction boxes for damage, corrosion, or water ingress
• Measure DC resistance between CAN H and CAN L at two points (expected ~60 Ω with both terminators present)
• Backprobe CAN H and CAN L with a diagnostic oscilloscope to verify proper differential waveforms and bit rate
• Check for bus-off status or high error counters in modules using a scan tool

Signal parameters

• Idle (recessive) voltage: CAN H ≈ 2.5 V, CAN L ≈ 2.5 V
• Dominant state voltages: CAN H ≈ 3.5 V, CAN L ≈ 1.5 V (differential ≈ 2.0 V)
• Typical differential amplitude (dominant): ~1.5–2.5 V
• Expected DC resistance across CAN H–L: ~60 Ω (two 120 Ω terminators in parallel)
• Common bus speeds: 125 kb/s, 250 kb/s, 500 kb/s (verify correct rate for vehicle)
• Acceptable bus load: well below saturation; high error/frame rates indicate faults

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