Code
U1719
FIAT
U — Network/User
CAN bus communication between engine control module and electric drive
AI status
Completed
Completed
100%
Causes
- Open, short or high-resistance wiring in the CAN high/low pair between ECM and electric drive module
- Corroded, bent or partially disconnected connector pins at either module
- Missing or failed CAN termination resistor(s) or incorrect termination
- Intermittent power or ground to one of the modules (ECM or electric drive)
- Failed CAN transceiver or internal module fault (ECM or electric drive controller)
- Low battery/unstable supply voltage during communication
Symptoms
- Electric drive or hybrid system warning lamp illuminated
- Reduced power, limited or limp-home mode for drive system
- Loss of expected data from electric drive on a diagnostic scanner
- Intermittent or persistent fault code storage and possible drivability issues
- No communication with the electric drive module when connected with scan tool
- Other CAN-related modules showing communication faults or cascade errors
What to check
- Read stored and pending DTCs and freeze-frame with a capable CAN diagnostic tool; note time stamps and related codes
- Check battery voltage and charge; verify stable supply (12V/24V depending on vehicle) while testing
- Visually inspect CAN wiring and connectors between ECM and electric drive for damage, corrosion or water ingress
- Wiggle test harness and connectors while observing live CAN data for intermittent changes
- Measure CAN high and CAN low voltages at both ECM and electric drive connector with key on, engine off
- Measure resistance across CAN H-L (bus disconnected from modules if required) to confirm ~60 Ω total
Signal parameters
- Idle single-ended voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (nominal)
- Dominant state voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
- Recessive state differential voltage ≈ 0 V (both ~2.5 V); dominant differential ≈ 2.0 V
- Typical bus termination: two 120 Ω resistors in parallel = ≈ 60 Ω across CAN H–L
- Common vehicle CAN data rates: 125 kbps, 250 kbps, 500 kbps (verify correct bus speed for model)
Diagnostic algorithm
- Read and record all network-related DTCs and freeze frame data. Note whether code is current, intermittent, or historical.
- Verify battery state of charge and system voltage. Repair charging or battery faults before continuing.
- With ignition ON, confirm communication presence on the CAN network using a high-quality scan tool; attempt to communicate with ECM and electric drive module.
- Perform a visual inspection of the CAN wiring harness and connectors between ECM and electric drive. Look for chafing, pinch points, heat damage, or water ingress.
- Measure CAN_H and CAN_L voltages at both module connectors with a digital multimeter and compare to expected signal parameters. Note any stuck high/low or open circuits.
- Disconnect modules only if safe and per manufacturer procedure. Measure resistance across CAN_H to CAN_L at ends of the bus to confirm ~60 Ω. If not, locate missing or damaged termination.
- Check for shorts to battery voltage or ground by measuring each CAN line to ground and to battery positive.
- Perform wiggle/drive-by tests while monitoring live CAN frames to reproduce intermittent faults and locate wiring movement faults.
- If wiring and terminations are good, swap or bench-test the suspected module (if serviceable) or scan for module-specific self-tests. Update software/firmware per manufacturer bulletins.
- Repair or replace damaged wiring, connectors, termination resistors, or faulty modules as indicated. After repairs, clear codes and perform functional verification and road test.
- If fault persists and wiring is confirmed good, consider module-level repair or replacement and consult manufacturer technical service information.
Likely causes
- Damaged harness section at routing points or near moving parts
- Connector corrosion or moisture ingress at module connectors
- Broken/crushed CAN wires inside loom, often at branch points or grommets
- Failed termination (open or wrong value) at one end of the bus
- Ground strap or battery negative connection with high resistance
- Intermittent module power supply due to blown fuse or poor contact
Fault status
Status
Lost or unreliable CAN communication between the engine control module and the electric drive controller. This may cause reduced drive capability, limp-home mode, and multiple related network fault codes until the underlying wiring, termination, power/ground, or module fault is corrected.
Repair difficulty: Medium
Diagnostic time: 1-4 hours
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