Gen 1 Prius Transmission Failure, P3009, P3120


(This blog is one in a series on Gen 1 Prius common failures.  Read the introductory blog here.)


Owners of the Gen 1 Prius (model years 2001, 2002, and 2003) are part of a group affectionately called “early adopters” and with that membership comes the imageburden of techno-drama (exclamation points, noises, et al.).  In that vein Luscious Garage could be equally named “Early Adopter Therapists”.  If it’s happening, we’re quite likely to witness it within our walls and to have the resources to help.

Such is the case of Gen 1 Prius transmission failures, which by now (some eight years after the model’s release) are nearly commonplace. (Pic is of the first bad trans we encountered—windings shorted to case—now serving as a plant stand in our downstairs lounge.)

The “classic” Prius has several unique features, including an undersized traction motor (a.k.a. MG2, the motor-generator directly connected to the wheels) of 30kW, versus the current model’s 50kW.  It also uses outdated transmission fluid,image Toyota Type T-IV, which is more prone to stress versus Gen 2’s WS (“world standard”).  Ventures into the transaxle case have uncovered additional rumor about a manufacturing defect chronicled by Art’s Automotive in Berkeley.  (Pic of torn pickup tube seal, courtesy of Art’s website.) It also suffers from voltage deficiency, relying on the main pack voltage rather than a boost converter (as with the Gen 2), which Physics translates to higher amperage and therefore higher load on circuitry.

The upshot is unwelcome warning lights (master, check engine, and/or red temp symbols), noise, and/or shuddering.  Codes may coincide or follow: P3009 “High Voltage Leak Detected” and/or P3120 (information code 250) image“HV Transaxle Assembly Malfunction, Motor Temperature Sensor Performance Problem”. (Pic of fried MG2 windings, perhaps due to lubricant, perhaps due to design, courtesy Jack Rosebro.)

HV leaks can be isolated using rudimentary techniques in the service bay.  A test drive with the scan tool reveals overheating problems.  The most recent patient, with only 61k miles on the clock, read over 300 degrees Fahrenheit after a mile of highway driving.

The fix is simple but expensive: replace the transaxle.  “Isn’t this exorbitantly expensive and enormous component serviceable,” you ask?  Well, yes, but you’ll pay as much in labor suffering through the process.  Reference again the chronicles of Art’s Automotive “Rebuilding a Toyota Prius Transaxle”.

[Hooray, this is no longer true!  Click here for the updated blog!]


LG offers two options for repair:

1.) USED: Replace the original with a salvaged version that may have the same penchant for problems but perhaps lower miles and less service neglect (translation: fluid changes, or lack thereof).  The labor is $100 more to cover transferring MG1 harness from original unit. (Pic of used transaxle)  Because it is increasingly difficult (near impossible) to find low mileage units, we can only transfer the 6 month PARTS ONLY warranty from the supplier.  (Expect 1-3 days lead time)

imageSecond hand transmission: $1200
New trans fluid: $26
New HV coolant: $20
Drain Plug gaskets: $3
Tax: $118.66

Installation: $1100
Alignment: $85

Total: $2552.66

2.) NEW: Replace the original with brand new from Toyota, PN 30900-47020, that you hope will last as long as the original and perhaps longer with the proper fluid service intervals. We are now offering the transmission unit *at cost* to incentivize this option, as it is a much better investment than a used unit. (Pic of new transaxle still in box; expect 1-3 days lead time)

imageNew transmission: $3000
New trans fluid: $26
New HV coolant: $20
Drain Plug gaskets: $3
Tax: $289.66

Installation: $1000
Alignment: $85

Total: $4423.66

3.) Once again, there is a far better alternative now!  Click here for the updated blog on transmission repair.

NOTE: Besides parts these prices also reflect a discounted labor rate of $100/hr.  We really want to help owners keep these cars on the road.

Is it worth it? The Gen 1, despite its flaws, is a feat of engineering and an overwhelming success of a vehicle, compared to all but the Gen 2 Prius (and perhaps its decendants: Camry, Highlander, and Lexus varieties).  But the “worth” of fixing ultimately depends on the attitude of the owner.

Hardly criticism, the story of Prius Transmission Failure is a cautionary tale of proper maintenance: change the transmission fluid every 30,000 miles, for all hybrids of this design (Toyotas, Fords, and Nissans).  It is the only service item in direct contact with the high voltage motor-generator(s) and the power-split device, to cool as well as lubricate these crucial components of the hybrid system.

For inquiries on transmission problems and repair, use the LG contact form.