Code
P1746
DAEWOO
P — Powertrain
Tcu l line
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the TCU L line circuit
- Corroded, loose or damaged connector at TCU or associated connector
- Short to battery voltage or short to ground on the L line
- Faulty TCU / TCM (internal circuit failure)
- Blown fuse or faulty power/ground feeding the transmission control circuits
- Intermittent connector contact due to vibration or water intrusion
Symptoms
- Transmission warning lamp / MIL illuminated
- Transmission may enter limp mode or default gear strategy
- Erratic or harsh shifts, or inability to shift to certain gears
- Torque converter lock-up may not engage (depending on circuit function)
- Intermittent transmission operation or reduced performance
- Stored P1746 code present in TCU/PCM memory
What to check
- Use a scan tool to read all stored/active transmission and powertrain codes and freeze-frame data
- Check battery voltage and charging system; low voltage can cause false faults
- Visually inspect TCU and transmission connectors for corrosion, bent pins, or contamination
- Inspect wiring harness for damage, chafing, broken insulation, or signs of overheating along the L line route
- Verify all related fuses and relays for the transmission/TCU are intact and seating properly
- Perform a wiggle test on wiring while monitoring live data and the fault status to try to reproduce the fault
Signal parameters
- Digital/logic line idle/high levels typically near vehicle battery voltage (approx. 0–12V depending on vehicle); low near 0V — verify against vehicle wiring diagram
- If line is PWM: duty cycle varies 0–100% when active — compare live data to expected behavior using scan tool
- Expected continuity on circuit wiring: low ohms between TCU pin and connector pin; open circuit indicates break
- Typical solenoid coils or driver outputs: coil resistance often in the low tens of ohms (e.g., 5–50 Ω) — verify against OEM spec
- Insulation resistance should be very high (no short to ground or battery)
Diagnostic algorithm
- Connect an OEM-level scan tool and note P1746 and any other related codes; record freeze-frame data and live sensor/actuator outputs
- Clear codes and attempt a road test or replication procedure while monitoring live data and the L line status
- Visually inspect the TCU connector and harness for corrosion, bent pins, water intrusion or physical damage; repair or replace as needed
- With ignition on (engine off) and battery supported, backprobe the TCU L line pin and measure voltage vs. ground; compare to expected idle/high values from wiring diagram
- Check for continuity between the TCU pin and the transmission connector pin; repair any open circuits
- Check for shorts: with battery disconnected, measure resistance from L line to battery positive and to chassis ground to detect inadvertent short circuits
- Inspect and verify transmission/TCU power and ground circuits; clean and tighten grounds and connector terminals
- If wiring and connectors check OK, perform bench or component tests on any associated solenoids or sensors referenced by the L line per OEM procedures
- If wiring, connectors and components test OK, consider TCU replacement or reprogramming only after confirming with OEM diagnostics and confirming no other modules cause the fault
- After repairs, clear codes and perform a full road test and verify no reoccurrence; perform any required adaptation/relearn procedures
Likely causes
- Open or damaged harness between transmission and TCU
- Corroded or bent pins in the multi-pin connector at the TCU
- Shorted L line to battery or ground due to chafing or pin-out error
- Failed TCU internal driver or input stage
- Lost ground or main power supply to the transmission electronics
Fault status
Status
Transmission Control Unit L-line circuit malfunction detected. Circuit fault may limit transmission function or force limp mode.
Repair difficulty: Medium
Diagnostic time: 1.0 - 3.0 hours
Similar codes
Repair manuals
Manual library for DAEWOO
75
Browse 75 DAEWOO manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.
DAEWOO
-
DAEWOO: 2001
-
Leganza
-
DAEWOO: 2000
-
Leganza
-
DAEWOO: 1999
-
Lanos
- S, 2D Hatchback, Automatic
- S, 2D Hatchback, Standard
- S, 4D Sedan, Automatic
- S, 4D Sedan, Standard
- SE, 2D Hatchback, Automatic
- SE, 2D Hatchback, Standard
- SE, 4D Sedan, Automatic
- SE, 4D Sedan, Standard
- SX, 2D Hatchback, Automatic
- SX, 2D Hatchback, Standard
- SX, 4D Sedan, Automatic
- SX, 4D Sedan, Standard
-
Leganza
-
Nubira
- CDX, 4D Hatchback, Automatic
- CDX, 4D Hatchback, Standard
- CDX, 4D Sedan, Automatic
- CDX, 4D Sedan, Standard
- CDX, 4D Wagon, Automatic
- CDX, 4D Wagon, Standard
- SX, 4D Hatchback, Automatic
- SX, 4D Hatchback, Standard
- SX, 4D Sedan, Automatic
- SX, 4D Sedan, Standard
- SX, 4D Wagon, Automatic
- SX, 4D Wagon, Standard
-
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email