What does it mean?
P1649 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Data Bus Powertrain Missing Message from ABS Control Module .
Symptoms
- MIL on together with ABS, stability control and often the brake warning lamp
- ABS and stability control disabled; normal braking remains but there is no anti-lock assistance
- Speedometer drops out or reads erratically
- Cruise control unavailable and the transmission may shift harshly because wheel speed data is missing
- Scan tool cannot communicate with the ABS module at all
Likely causes
- ABS module unpowered: blown fuse, failed relay or a bad power/ground connection at the unit
- Open or shorted CAN high or CAN low wire between the ABS module and the rest of the bus
- Corroded connector at the ABS hydraulic unit, which sits in a wet area of the engine bay
- A shorted node or a missing terminating resistor pulling the whole bus down
- Internal failure of the ABS control module
- ABS module replaced but not coded to the vehicle
- Harness damage after brake, suspension or body repair work
How to fix it
- Try to communicate with the ABS module first; a total no-response points at power, ground or bus wiring rather than a lost message
- Check the ABS fuses and relay, then measure module supply voltage and ground under load with voltage-drop tests
- Unplug and inspect the ABS connector for water, corrosion and bent or pushed-out pins
- Measure resistance between CAN high and CAN low at the diagnostic connector with the ignition off; roughly 60 ohm indicates an intact bus with both terminating resistors
- Disconnect the ABS module and see whether the rest of the bus recovers, which isolates a shorted node
- Inspect the harness where it passes the wheel arch and any recently repaired area
- Replace and code the ABS module only after wiring, power and ground are proven good