OBD2 U0404

Severity

Summary

Code U0404 indicates that the powertrain control module has received invalid data from the gear shift control module. This issue is related to the transmission or body control systems.

Symptoms

• Reduced transmission performance
• Diminished engine fuel efficiency and performance
• Erratic transmission shifting patterns
• Illumination of service engine soon lamp, traction control lamp, or antilock malfunction lamp
• Inoperative speedometer
• Inoperative paddle shifter/s
• Inoperative mode selector switch

Common Causes

• Defective system power relay
• Corroded or damaged fuses or fusible links
• Loose, corroded, or disconnected ground wires and/or straps
• Cut, burnt, or otherwise damaged wiring harnesses or connectors
• A defective gearshift module
• A defective PCM or transmission controller

Diagnosis

1. Inspect all system wiring, connectors, battery, cables, and terminal ends.
2. Test fuses, circuit breakers, and power supply relays.
3. Use a diagnostic scanner to check the gearshift module's output signal.
4. Verify mechanical aspects of the gearshift mechanism.
5. Check for proper system power and ground signals.
6. Inspect resistance and continuity on individual system circuits.

Fixes

• Replace defective parts such as fuses, relays, or wiring harnesses.
• Repair or replace the gearshift control module if it is faulty.

FAQ