Code
P1780
DAEWOO
P — Powertrain
Eng torque sig err(can comm)
AI status
Completed
Completed
100%
Causes
- Loss of CAN/communication between ECM and TCM
- Damaged/shorted wiring or poor connector/terminal contact on torque or CAN lines
- Faulty ECM or TCM (internal failure)
- Incorrect or outdated module software/calibration
- Low or unstable battery/charging system voltage
- Intermittent ground or power supply to one of the control modules
Symptoms
- MIL/Check Engine light illuminated
- Transmission may go into limp mode or default shift strategy
- Erratic, harsh, delayed, or missing shifts
- Torque converter lockup problems or unusual torque management behavior
- Loss of adaptive shift learning or degraded drivability
- Customer complaint of shudder or surging under load
What to check
- Read all stored and pending DTCs from ECM and TCM; record freeze frame data
- Check for related U-codes (CAN/communication) or other engine/transmission codes
- Verify battery voltage and charging system while key on/engine running
- Visually inspect wiring and connectors at ECM and TCM for damage, corrosion, or water intrusion
- Check module grounds and power circuits for integrity and voltage drop
- Using a scan tool, monitor live data: engine torque value, RPM, throttle/pedal position, and message presence from ECM to TCM
Signal parameters
- Engine torque value reported by ECM (live-data parameter) — should update with throttle/RPM changes
- Engine speed (RPM) — must be present and stable
- Throttle position / accelerator pedal position — should correlate with torque value
- Battery voltage (key on and cranking) — nominal ~12–14.5 V
- CAN bus: CANH ~2.5–3.5 V, CANL ~1.5–2.5 V (idle); differential signal typically 0.5–2.0 V
- CAN bus termination: approx. 60 ohms between CANH and CANL (ignition on)
Diagnostic algorithm
- Connect a capable scan tool to both engine and transmission modules; record all codes and freeze frame; note other U-codes.
- Check battery and charging system: ensure battery fully charged and charging properly; low voltage can cause comm errors.
- Monitor live data: watch engine torque value and verify it updates when throttle/RPM change. Check for missing or frozen values.
- Inspect connectors and wiring at ECM and TCM for corrosion, bent terminals, water ingress, or recent service damage. Repair any damaged connectors.
- Check power and ground circuits to ECM and TCM: measure voltages and continuity to chassis ground; repair poor grounds.
- Measure CAN bus voltages with key ON: verify CANH/CANL voltages and ~60 Ω termination. If voltages out of range, isolate short/open segments and repair harness.
- If a dedicated analog torque signal exists, backprobe the signal wire and verify voltage changes with throttle/RPM and check for shorts to voltage or ground.
- Perform a wiggle/drive test while monitoring live data to identify intermittent harness faults.
- If wiring and power/grounds are good, consult OEM service information for module reprogramming bulletins; reflash/update module software if required.
- If software update not applicable and fault persists, consider swapping in a known-good TCM or ECM (per manufacturer procedure) or replacing the failed module. After repair, clear codes and perform a road test to confirm fault does not return.
Likely causes
- Open/short in dedicated torque signal wire or CAN bus wiring
- Corroded/loose connector at ECM or TCM
- Faulty TCM or ECM communication driver
- Battery/charging voltage too low causing communication errors
Fault status
Status
Engine torque signal error — communication fault (ECM → TCM).
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.
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DAEWOO: 2001
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- 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
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