Code
P5000
CITROEN
P — Powertrain
Communication malfunction between ECM and other computers (CAN)
AI status
Completed
Completed
100%
Causes
- Open, shorted or corroded CAN bus wiring or connectors
- Faulty ECM or another control module driving the bus incorrectly
- Missing or failed CAN termination resistor(s)
- Poor battery/ground or supply voltage to ECM or other modules
- Intermittent connector contact or water ingress
- Aftermarket accessory interfering with the CAN network
Symptoms
- MIL (engine warning light) or communication warning illuminated
- One or more vehicle systems non-responsive or behaving erratically (instrument cluster, ABS, airbag, transmission, etc.)
- Intermittent faults that come and go with vibration or temperature change
- Inability to communicate with ECM or other modules with a scan tool
- Possible no-start or limp mode if critical modules lose communication
What to check
- Read all stored DTCs and freeze frame data from all modules on the network
- Check battery voltage and main chassis/engine grounds (clean/tighten as needed)
- Inspect CAN bus connectors and wiring for damage, corrosion or water entry
- Verify fuses and power feeds to ECM and other modules
- Measure resistance across CAN_H and CAN_L with ignition OFF (approx. 60 ohm typical)
- Use scan tool to list which modules respond on the CAN network
Signal parameters
- Recessive idle voltage: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both near mid-rail)
- Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
- Bus differential voltage when active ≈ 1.5–3.0 V depending on load
- Termination resistance across CAN_H and CAN_L ≈ 60 Ω (two 120 Ω terminators in parallel)
- Common CAN bit rates in vehicles: 125 kb/s, 250 kb/s, 500 kb/s (verify manufacturer network speed)
Diagnostic algorithm
- Record all codes and symptoms from every control module. Note if code is permanent or intermittent.
- Verify battery condition and main grounds. Repair/clean any poor connections and re-check.
- Visually inspect CAN wiring, connectors and junctions for damage, corrosion or moisture. Repair any damaged sections.
- With ignition OFF measure resistance between CAN_H and CAN_L at a convenient connector — expect ~60 Ω. If open or very high, locate missing terminator or open circuit.
- With ignition ON (engine off), measure DC voltages: CAN_H and CAN_L should sit near 2.5 V. If one line stuck to 0 V or battery voltage, isolate and repair short.
- Use an oscilloscope to view CAN_H and CAN_L waveforms while a scan tool is communicating. Look for missing frames, dominant stuck states, or excessive noise.
- Disconnect suspected non-essential modules one at a time (or isolate network segments) to determine if a specific module is pulling the bus down.
- Replace or repair the faulty wiring, connector or module identified. If a module is replaced, follow manufacturer programming/re-initialization procedures.
- Clear codes, perform functional tests and a road test. Re-scan all modules to confirm the fault is cleared and no other related codes remain.
- If fault persists despite good wiring and termination, consider ECM or other module CAN transceiver failure and consult manufacturer service information for module bench tests or replacement procedures.
Likely causes
- Damaged wiring harness or chafed insulation causing short to ground/Vcc
- Failed CAN transceiver inside ECM or another module
- Lost ground or low battery voltage at ECM
- Disconnected or corroded CAN connector(s)
- Open or high resistance in termination resistors (expected ~60 ohm across bus)
Fault status
Status
Communication fault stored by ECM: message loss/corruption on CAN bus. Fault may be intermittent or permanent. MIL/warning may be set depending on affected systems. Freeze frame and additional module codes should be consulted for scope and timing.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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