Tesla Model S (2014–2016) Rear Drive Unit (LDU) Isolation Fault (Coolant Ingress)
Tesla LDU corrosion / water ingress
Tesla rear drive unit fault
Tesla Model S won’t start / won’t drive
The following fault code(s) may be present
P0AA6 - High Voltage Isolation Fault
BMS_w035 - SW Isolation warning
BMS_a035 - SW Isolation alert
BMS_a151 - SW External isolation alert
BMS_w142 - HV insulation/isolation-related warning
BMS_F123 - HV insulation/isolation-related fault
Do you have a Tesla Model S that’s showing an isolation fault, or has suspected drive unit (LDU) coolant ingress?
Don't ignore it. Book an initial inspection today and get expert help.
Parts Repaired or Replaced
- Stator
- Inverter
- Transmission input shaft bearing
- High voltage cable set
Affected Vehicles
Tesla Model S
- Tesla Model S 2014
- Tesla Model S 2015
- Tesla Model S 2016
Common Failure Symptoms
- Vehicle faults to a non-drive state
- Isolation fault (loss of isolation) warnings
- Coolant ingress / contamination leading to corrosion within the drive unit
- Milling sound coming from rear end of vehicle (typical with this failure)
- Drive unit performance concerns
Tesla Model S Diagnostic Report
Initially, the vehicle arrived following an isolation fault diagnosis at the rear drive unit, but live isolation testing was not possible as both rear motor high‑voltage cables had been cut, preventing the contactors from closing. Subsequently, we removed the rotor‑side speed sensor and used a periscope inspection to check inside the housing, where coolant was found in an area it should not be. Based on the isolation concern and evidence of coolant ingress, we proceeded with a strip down and test.
Tesla Model S Repairs
Further investigation confirmed coolant, rust and water contamination on the stator and corrosion on the inverter side of the LDU. Following testing, the stator was verified as non‑repairable and sent away for replacement. For best use of time and cost effectiveness, the inverter was replaced, and the transmission input shaft bearing was renewed due to roughness.
- Stage 1 LDU overhaul completed
- Stator replacement completed
- Inverter replacement completed
- Input shaft bearing replacement completed
- Coolant delete completed
- High voltage cable set replaced
Resolution
The rear drive unit was overhauled and rebuilt with replacement components where required, addressing coolant ingress and internal corrosion concerns identified during diagnosis.
Following the repair:
- Drive unit rebuilt with replaced stator and inverter
- Bearing issue resolved with new input shaft bearing
- Coolant delete and HV cable set installed as part of the overhaul scope
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