MPU not working as expected
1. If this DTC #549 appear rarcly and not toaghter with one of the following DTC:s #548, #550, #551, #552, #553 it is most probably set on a false basis and the MPU works as expected and do not need to be replaced. To verify that it is no cable malfuction that has caused DTC#549 Check accoring to 2.2 and 2.3 below. A software update for the above false behavior will be available in September 2020. 2. If DTC #549 has been set togather with any one of: DTC #548, #550, #551, #552 or #553 please follow the investigation procedure below: 2.1. Check power supply connection for corrosion: - Switch battery OFF - Remove MPU pole cover - Thoroughly inspect the plus pole cable ring terminal, the associated M6 nut, and the cable wire where it is crimped to the ring terminal, for corrosion. >> If corroded, the ring terminal, nut and wire/cable, must be replaced as a set. >> If the terminal screw on the MPU::eMotor is badly corroded, the eMotor must be replaced as well. 2.2. Check power supply to MPU electric motor: - Remove MPU pole cover - Switch battery ON (connections / master switch) and measure voltage on MPU power terminals (M6 screws). It should be approximately 24 volt (battery voltage). - Switch battery OFF - Check tightening torque for both M6 terminal nuts, and ground cable connection to frame. - Check the MPU fuse - Visually inspect the isolation along the entire cable length, for abrasion damage that could lead to a short circuit against frame or similar. 2.3. Check MPU enable signal for short circuit to supply voltage: - Disconnect ECU pin A27 (in the ECU connector) - Turn on battery supply (30) and ignition (15) - Measure voltage level in the disconnected cable harness wire - should be zero volt 2.4. Check MPU enable signal for open circuit, or short circuit to ground. - Pin A27 in ECU connector, and pin C6 in MPU connector. 2.5. Check MPU enable ground return signal for open circuit, short circuit to ground, short circuit to supply voltage. - Pin A25 in ECU connector, and pin C5 in MPU connector. 2.6. Test for intermittent SW failure: - Run diagnostic SelfTest - Check if DTC turns passive. - If DTC is still active - erase all DTC and re-run diagnostic SelfTest. - Drive vehicle and make sure DTC not appears again. - If DTC reappears error trace MPU 2.7. If the fault can not be found, by procedures above, replace the electric motor (M53) in the MPU. Verify that the issue is solved by performing a Diagnostic SelfTest (requires Parking Brake to be applied) - If the root cause fault has been fixed, this DTC will be set passive.
What you'll see
No driver-visible symptom recorded.
System reaction
Red Steer tag axle fault warn EST in released or fixed mode
Diagnostic depth
The electric motor (M53) in the MPUis not working as expected. This could be caused by a poor power supply connection. One of the following faults has been detected: • Checksum error on CAN message from MPU eMotor • Counter error on CAN message from MPU eMotor • Feedback signals indicates error in MPU eMotor • MPU eMotor internal self-test has failed
1. Failed eMotor self test due to instable imput voltage from the vehicle. This is the cause only if none of the following DTC:s are set at the same time: #548, #550, #551, #552, #553 2. DTC549 in combination with one of the following DTC:s #548, #550, #551, #552, #553 the cause is one of the following: • Corrosion on plus connection • Power terminal nuts are loose • Faulty Cable harness - supply or ground Other possible faults: • Short circuit (to supply) on the MPU enable signal (ECU pin A27). • MPU SW bug (intermittent temporary fault) • Electrical fault in MPU motor (M53)