MPU electric motor is stopped due to low supply voltage
• Check batteries. • Check electrical connections for corrosion, and check tightening torque on nuts. - Gently remove the MPU pole cover, and inspect the positive and negative terminals (M53::B2 and M53::B1). - MPU grounding point in frame (G77) - Fuse box (P11) • Check power supply wiring to MPU, for abration damage etc. (open circuit, or short circuit). • Check MPU internal voltage sensor: Measure the supply voltage between signal and ground. - Switch on battery (connections / master switch) and ignition key (15). - Measure voltage on MPU power terminals (M6 screws), using a multi-meter device. It should be approximately 24 volt (battery voltage). - Compare measured value to value read from CID 0xF487 (MPU supply voltage), using SDP3. - If there is a significant divergence/difference (more than 5 volt) the electrical motor (M53) in the MPU has to be replaced. - N.B. Make sure to compare values, from multi-meter and SDP3, sampled at the same time (as battery voltage can fluctuate over time, depending on active consumers). 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
MPU (component code M53) has detected low supply voltage.
• Defect vehicle batteries • Defect connectors/connections (e.g. corrosion) - MPU positive pole connection defect - MPU negative pole connection defect - MPU ground connection in frame defect - MPU power supply fuse (100 A) defect • Defect wiring - open circuit on MPU power supply or ground harness - short circuit on MPU power supply harness • Defect MPU (internal voltage sensor) - N.B. very unlikely - has to be verified before component M53 is replaced! Refer to "Action".