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Home / DTC / P1671 — Can comm flt - tcu modl sig indc

P1671 — Can comm flt - tcu modl sig indc

Detailed page for trouble code P1671.

34,401codes
59brands
11,910generic
22,491specific
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Code

P1671

DAEWOO P — Powertrain

Can comm flt - tcu modl sig indc

Brand: DAEWOO
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or short in CAN-H or CAN-L wiring
  • Corroded/loose connector at TCU or junctions
  • Failed Transmission Control Module (TCU)
  • Failed PCM/BCM or another module interfering on the CAN bus
  • Missing or low power/ground to TCU (fuse, wiring, battery)
  • Poor CAN termination (open or incorrect resistor)

Symptoms

  • MIL / transmission warning lamp illuminated
  • TCU not responding to a scan tool or intermittent connection failures
  • Transmission stuck in limp mode or only limited gears available
  • Erratic or harsh shifting, incorrect gear indication
  • Other modules reporting CAN communication errors or loss of messages
  • Possible no gear/shift indicator on dash

What to check

  • Scan vehicle with a capable diagnostic tool; record P1671 plus any U-codes or other related DTCs and freeze-frame data
  • Attempt to communicate directly with the TCU; note if tool can read live data
  • Visually inspect TCU connector, transmission harness and any CAN junctions for corrosion, bent pins, water damage or repairs
  • Check fuses and power/ground circuits to TCU for proper voltage and continuity
  • Measure CAN bus termination resistance between CAN-H and CAN-L with ignition off (approx. 60 ohms)
  • With key on, measure CAN-H and CAN-L voltages at TCU connector and other nodes

Signal parameters

  • CAN idle voltages (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each relative to ground)
  • CAN dominant voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (approximate)
  • Differential voltage dominant ≈ 2.0 V; recessive ≈ 0 V
  • Termination resistance ≈ 60 Ω measured between CAN_H and CAN_L (two 120 Ω in parallel)
  • Typical data rates: 250 kbps or 500 kbps (vehicle-specific)
  • Expected module responses: TCU should acknowledge/respond to diagnostic requests and broadcast shift/status messages at defined intervals

Diagnostic algorithm

  1. Connect full-function scan tool; read and record all codes and freeze-frame data. Note any U-codes (lost communication) along with P1671.
  2. Attempt communication with TCU. If tool cannot communicate, confirm whether other modules respond to narrow scope.
  3. Check battery voltage; ensure stable supply (12.6 V at rest, ≥11 V cranking) and inspect fuses/relays powering the TCU.
  4. Visually inspect TCU connector and harness for damage, corrosion, bent pins, or fluid ingress; repair or clean as needed.
  5. With ignition off, measure resistance between CAN_H and CAN_L at TCU connector — expect ≈60 Ω. If open or very low, isolate to find short/open.
  6. With key ON (engine off), measure CAN_H and CAN_L voltages at TCU and at a known-good node. Compare to expected values; look for stuck high/low or no signal.
  7. Perform wiggle/short tests: gently move harness and connectors while monitoring for code changes or lost communications to find intermittent faults.
  8. If basic checks OK but communication errors persist, use an oscilloscope to view bus waveforms for noise, reflections, or missing frames. Compare waveforms to a known-good waveform.
  9. Isolate the problematic segment by disconnecting branches or modules one at a time (where safe) to identify a faulting device or harness section.
  10. If wiring and terminations are good and the bus is otherwise healthy, reflash TCU software per factory procedure; if a module still fails to respond or shows internal transceiver failure, replace TCU.
  11. Clear codes and road-test to confirm repair; re-scan to ensure no new/returning CAN communication codes.

Likely causes

  • Corroded harness connector at TCU or water intrusion
  • Broken or chafed CAN wires near transmission or chassis harness
  • Blown fuse or poor ground to TCU
  • Failed TCU internal transceiver
  • Faulty termination resistor (open or shorted) causing bus errors
  • Intermittent contact from damaged pin/solder joint

Fault status

⚠️ Status
CAN communication fault detected involving the Transmission Control Module (TCU). TCU signal or message(s) missing, intermittent, or invalid on the vehicle CAN bus. Investigate wiring, power/ground, termination, and module integrity.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-4.0 hours

Similar codes

U0073 U0100 U0101 U0140 P0700
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