Code
P1602
DAEWOO
P — Powertrain
Ecu - tcu comm mal
Views:
UK: 8
EN: 11
RU: 11
AI status
Completed
Completed
100%
Causes
- Damaged or corroded wiring harness between ECM and TCU
- Loose, corroded or improperly seated connectors at ECM, TCU or junctions
- Blown fuse(s) or missing power/ground to TCU or ECM
- Faulty TCU (transmission control module) or ECM
- Faulty CAN transceiver or bus driver in one module
- Short or open in CAN/communication lines, or high resistance in bus
Symptoms
- Malfunction Indicator Lamp (MIL) or transmission warning light illuminated
- Transmission may go into limp/safe mode or default gear
- No communication with TCU when scanning (module not present) or intermittent presence
- Erratic or harsh shifting, failure to shift, or stuck in one gear
- Engine may hesitate or reduced driveability if modules can't coordinate
What to check
- Use a proper scan tool to read stored/active DTCs and check for presence of ECM and TCU on the network
- Verify battery voltage is within specification during tests (typically >12 V) and check charging system
- Inspect fuses and relays supplying power to ECM and TCU
- Visually inspect connectors, pins, and wiring between ECM and TCU for corrosion, damage, or loose pins
- Check for other U‑codes on the CAN bus and note module addresses that do or do not respond
- Perform wiggle test on harnesses while monitoring communication status (safe to do with vehicle stationary)
Signal parameters
- CAN bus idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (typical); dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V
- Differential CAN termination: expected combined bus resistance ≈ 60 Ω (two 120 Ω terminators in parallel) between CAN_H and CAN_L
- Module supply: TCU/ECM Vbatt ≈ battery voltage when key ON
- Ground: low resistance (
Diagnostic algorithm
- Connect a professional scan tool and confirm P1602 plus any other stored codes; note whether TCU appears in module list
- Record freeze frame or pattern of failures (intermittent vs permanent) and attempt to reinitialize modules (key cycle, battery disconnect only if allowed by manufacturer)
- Verify battery voltage and charging system; ensure stable supply before electrical diagnosis
- Inspect and reseat connectors at the ECM, TCU and any intermediate junctions; look for corrosion, bent pins or water ingress
- Check related fuses/relays for continuity and proper supply to modules
- With ignition ON and key in start-safe state, measure CAN_H and CAN_L at TCU and at ECM; confirm idle voltages and that differential/termination is present (≈60 Ω across bus)
- If CAN voltages abnormal, trace wiring for opens/shorts to power or ground; repair wiring or connector faults
- If bus physical layer is good but module does not respond, disconnect suspect module(s) one at a time to see if network recovers or other modules appear; isolate the faulty module
- Attempt to communicate with TCU using manufacturer diagnostic tool; if module responds intermittently, consider module replacement or repair
- Check for available software updates or known technical service bulletins; reflash or reprogram modules per manufacturer procedures if recommended
- If all wiring and power/ground checks pass and reprogramming fails, replace faulty module as last step and clear codes; retest and verify repair
Likely causes
- Poor connector/terminal contact at TCU or ECM
- Open/short in CAN high or CAN low between modules
- Failed TCU or failed ECM (module not responding on the bus)
- Blown fuse, missing power or bad ground to TCU
- Corroded/jammed wiring at a splice or junction box
Fault status
Status
Communication fault recorded: ECU (engine control) and TCU (transmission control) not communicating on vehicle network (CAN). Condition may be intermittent or permanent and can disable normal transmission control.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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