Gen 1 Prius Transmission Repair, P3009, P3120, P3125

(This blog supersedes “Gen 1 Prius Transmission Failure” dated 10/28/2008.)

imageFirst generation Prius are prone to transmission failure.  99 times out of 100 the issue is a bad MG2 stator. Winding insulation degrades, creating a short between turns and/or phases.  Heat from the short (high current) burns through surrounding insulation, broadening the affected area.  Common symptoms can include:

1. Shudder during takeoff
2.    Louder whine during regenerative braking
3. Temperature warning light (red thermometer)
4. Master Warning Light (red triangle)
5. Diagnostic Trouble Codes (DTCs):

P3009: HV Leak to Ground
P3125, info code 287: Inverter Internal Short
P3120, info code 250: HV Transaxle Assembly Malfunction, Motor Temperature Sensor Performance Problem

Stator degradation can be confirmed in the service bay; LG maintains the necessary diagnostic tools and leads the industry in expertise.  All information is shared with the vehicle owner and documented in the work order.

Until now it was deemed cost prohibitive to service the motor rather than replace the entire unit.  In the last six months, however, two significant discoveries have been made:
1. It is possible to remove and replace the MG2 stator from behind the assembly endplate, with negligible disturbance to the motor resolver.

2. A replacement stator can be harvested from an MG2 assembly, available brand new from Toyota for a third of the price of the entire transaxle.

The result is a reliable service procedure that saves significant time and money.  Repair strategies of the past—replace the entire transaxle with brand new, replace the entire MG2 assembly with brand new, or replace the entire transaxle with used—are effectively obsolete.

The cost breakdown for stator replacement is as follows:

Labor, R&R MG2 Stator: $1080
MG2 Motor Assembly, Hybrid (Toyota P/N G1100-47040): $1288.74
ATF, Drain Plug Gaskets, Coolant: $47.39
Sales Tax: $126.01

Total: $2533.45

Other foreseeable costs:
Initial diagnosis: $60
Additional diagnosis with milliohmeter, megohmmeter, or impedance tester (if required): $100
HV Battery Test (to anticipate other high dollar repairs): $50

For questions or to book an appointment, use the contact page.

While not inexpensive, this repair significantly reduces the monetary and material cost of Gen 1 Prius ownership, postponing the day when a fuel-efficient car has to be replaced.

Credit for this service procedure goes to Jack Rosebro of Perfect Sky Hybrid Training.  For classes call 310-383-4800.

We publish our services online to promote ourselves and to inform hybrid owners of their service choices.  This is a complex procedure, and should not be undertaken without proper instruction.


View of the transmission endplate tilted into the wheel well:


MG2 rotor and stator removed together:


Typical view of burned windings:


Transaxle housing with stator and rotor removed:


MG2 assembly out of the box from Toyota:


View of MG2 stator with endplate removed, to be harvested:


New stator installed with original rotor: