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Wednesday, August 31, 2011

Gen 2 Prius (2004-2009) Transmission Failure, P0AA6, P0A92, P0A7A

Long ago we published a blog on Gen 1 transmission failure (superseded to yet another blog here).  Around the same time we predicted Gen 2 transmissions would be more robust.  While this remains statistically true, our experience has proven that they are not immune to transmission problems of their own.  Common symptoms include:

1. Whining/growling noise when engine starts
2. Rattling/banging when driving
3. Car refuses to “ready”
4. Engine cannot start (“rizz” noise when cranking)
5. Master warning light (red triangle)
6. Diagnostic trouble codes:

P0AA6, info codes 526, 613: High Voltage Isolation Fault
P0A7A: Generator Inverter Fail (over current by inverter assembly malfunction)
P0A92: MG1 malfunction

LG currently operates an overnight shift 7 days a week dedicated to hybrid taxi cabs.  With this experience we can describe Gen 2 Prius transmission failure as routine, somewhere between 150-250k miles.  The most common indication is trouble code P0AA6 (no other symptoms), but we have also seen broken chains, failed bearings, bad MG1s (trouble code P0A7A and P0A92), and seized planetaries altogether. 

We have also seen these problems on private cars, as they get older.  Our original poster child (see the 250k mile Prius blog) is now outpaced by many a commuter and second owner, and our experience is far more informed.  Not only have we seen failures, in the process we’ve developed industry-leading procedures for testing insulation, impedance, and mechanical problems.  We are ahead of the dealer.

Upshot: if your car has a problem we can isolate the source (be it transmission OR somewhere else).

imageNot only can LG navigate the jungle of diagnosis to provide a GUARANTEED repair, we can repair the car at a fraction of dealer cost with second hand units and honest labor charges.  Over the years we have replaced dozens of Gen 2 Prius transmissions to the point that we keep several used units in stock (pic of our “large parts” inventory).  We also stock inverters, batteries, simple sensors, and ECUs.  We are capable and prepared to fix your car.

For more on individual problems, keep reading.  To skip to prices, CLICK HERE.


The generic information code is 526, and the transmission specific info code is 613.  While there are other potential causes of P0AA6, the most common by far is winding deterioration in the traction motor (MG2). 

The Gen 1 equivalent of P0AA6 is P3009, and when it sets the car will continue to ready on and drive normally.  With Gen 2 Prius, the car will not allow the car to restart once the code sets.  Toyota engineers decided HV faults were highly dangerous and the car was unsafe to drive.  On the Gen 3 Prius, the trouble code is the same (P0AA6) but the car will still ready and drive.  Thus we can interpret that Toyota admits this condition is not that unsafe after all.

Taxi drivers are tenacious as hell, and those commissioned to Gen 2 Prius often resort to disconnecting the 12v battery (or pulling the necessary fuses) to erase the P0AA6 and continue driving.  I’ve seen them drive for months without repair (one went so far as to install a quick disconnect handle for the 12v in the trunk).  Eventually the car developed another problem (more on this later) which necessitated a transmission replacement.

Needless to say, except for the prohibition of “ready” mode, the car will drive normally.  For dealer techs unfamiliar with it, the problem is mysterious; most recently a customer came to us for diagnosis after the dealer already installed an inverter (at no small charge) despite the information code 613 (pointing to the transmission).

Unless the winding is seriously deteriorated, it is rare that P0AA6 will set when the transmission is cold; only after driving several miles under load (taxi/highway) will the insulation in the windings lower enough to set the code.  This is a case where the technician cannot confirm that the problem is inside the transmission (at least without getting the assembly suitably hot before performing an insulation test).  The car’s diagnostics (which will automatically test each HV branch to help isolate the source of the leak) aid in this regard.  For instance, the information code 612 points to the HV battery (rather than the transmission) which can direct the technician to look for damaged battery modules, leaking electrolyte to the chassis (ground).

In California, P0AA6, info code 526 AND 613 is covered under warranty up to 150,000 miles; see:

Toyota Technical Service Bulletin T-SB-0306-08 MIL ON DTC P3009 or P0AA6, Information Codes 526 & 613

Other transmission issues not covered under warranty are below.

Transmission noise:

There is a flat needle bearing that holds the planetary gearset from the MG1 case.  This bearing is the weakest mechanical link, prone to failure over time.  Once it collapses, the gear it supports falls inward against the load of the chain and grinds into the case of MG1.  Early signs are a whine when the engine starts (or runs).  imageLong term the chain will break and when MG1 attempts to crank the engine the planetary freewheels with a “rizzing” sound.  See the video taken over a year ago of cab 178, dedicated to our favorite hybrid instructor Jack Rosebro:


We’ve also seen a support bearing in the final drive fail; symptoms are rattling when moving or banging when slowing or starting.  The cause is excessive movement in the final drive with the gear out of place.  Eventually the stress will crack the case, causing a transmission fluid leak, a broken chain, or a seized gear.

P0A7A, P0A92:

Winding deterioration is also possible in MG1, the smaller motor/generator inside the Toyota HSD transmission.  Symptoms may be similar to the noises of a bad bearing or broken chain, because MG1 is engaged when the car attempts to crank the engine.  Sometimes the gearset makes noise (the motor’s shorted windings will shudder, and the gearset will clatter accordingly), but sometimes the motor is bad enough that the inverter will simply default when attempting to engage it, much like a bad starter making a single “click”.  When attempting to “ready”, the click is heard and then the warning lights appear, and the car is incapable of starting the engine.  The vehicle will still move under the power of MG2 (the traction motor) but the HV battery will eventually deplete to the point that it will ready off and it will no longer attempt to restart (“ready”) at all.

Both of the trouble codes relate to the inverter, which is why it is so often condemned as the source of the problem.  The inverter provides power to the motors, and with a short the inverter current will peak, setting a code.  This is exactly the same scenario as P3125, info code 287 with Gen 1 Prius.  Sadly I expect many an inverter will be thrown at Gen 2 Prius, despite the experience with earlier models.  This is entirely a case of “killing the messenger”.


What of repairing these problems, rather than replacing the whole unit?  It’s a good question.  At this point there is no source for MG1 or MG2 windings, bearings, or gears outside of the total unit.  We do occasionally get salvage units that are half good (cracked on one end, for instance) that can be used for parts.  But by in large the effort to rebuild a unit is as much labor/parts as the total assembly ($800 used), with the additional liability imageof one of the aforementioned problems developing.  As our cache of good used parts grows, we may find this a better option, especially as the demand for used units goes up.  At this point our approach is to gather as many good low mileage units as we can afford.


As of this blog we are able to find used Gen 2 Prius transmissions with low mileage at a reasonable price ($800).  After dozens of jobs, only recently did we encounter a used unit with the faintest beginning of a needle bearing noise, which we replaced a second time on the house, as part of the original job.  In short, while we are confident in the reliability of used units, we are very careful to install ones without issue and extend a one year, 12,000 mile warranty against transmission problems.

Labor: $1,360
Transmission (Used Unit): $800
Additional Parts (seals, axle nuts, fluids): $89.29
8.25% Sales Tax: $75.48

Total: $2324.77

To book an appointment, use the contact page.

Carolyn's avatarPosted by Carolyn Permalink Categories: Repair »

Monday, August 08, 2011

Prius Battery Rebuild: Yes or No?

Our original blog on Prius battery failure vaguely describes rebuilding HV packs as one of the services we offer.  Since it was published (over two and a half years ago) HV battery diagnosis and repair has become common place.  On average our shop sees at least one battery failure per week, and countless more are being replaced at the dealer and other Bay Area independents.

About a year ago I published another blog to streamline the conclusions from the original.  The emphasis was rebuilding, written at a time when our in-house rebuilds were at their peak: in frequency, ease, and success.

Today’s blog focuses on increasing complications rebuilding HV batteries based on our continuing experience.  It is written to help decide which route to take (new or rebuilt) mostly for those web-savvy folks teasing out alternatives across the country.  It is detailed for those seeking the most information.

To summarize earlier blogs, the basis for rebuilding is three-fold:

1. Better technology

Second generation Prius (Gen 2) modules are improved over Gen 1, but still fit in a Gen 1 battery chassis

2. Available parts

Gen 2 Prius are more common, making used battery packs easy to obtain

3. Less expensive

Despite additional labor to rebuild, the total job amounts to $600+ savings over brand new
Given these factors, why not rebuild?  It’s no surprise our customers have overwhelmingly chosen rebuilt packs.  It’s ideal for us: we can save people money while making more money ourselves (in labor, rather than just paying Toyota for the new part). 

As time goes on, however, these factors are no longer cut and dry.  We have also discovered pitfalls in the process itself.  What’s new:

1. Competition for parts

2. Growing awareness of Gen 2 battery issues, in their own right

3. Growing awareness of battery module damage due to over-handling

I will extrapolate on each of these below.


While I don’t honestly perceive LG as “ahead of the curve” on these repairs, the wave of failures has definitely crested since we opened in 2007.  This trend has increased demand for parts AND other businesses willing to meet that demand.  While we may have had some influence in consumers’ willingness to rebuild (acknowledging the process as doable, and discussing it online), many other sites (PriusChat et al.) discuss its feasibility. 

ReInvolt was the first business (to my knowledge) to sell rebuilt packs to the public (across the US, not just customers in a shop).  We discovered them in September of 2009, and I had the pleasure of meeting Dave Taylor at ASE headquarters in Virginia shortly thereafter.  Their business has put a high demand on the Gen 2 packs on the east coast region, and ReInvolt has become the leading representative for Prius battery rebuilding.

In the middle of last year, we noticed a shortage of Gen 2 packs on the west coast.  My rep at LKQ narrowed the purchases to “Battery Boy” in Healdsburg, CA, just north of San Francisco.  The shortage of packs made it increasingly difficult for us to “match” modules into a pack. (Gen 1 packs are 38 modules, while Gen 2s are 28; thus to make a Gen 1 pack from Gen 2s you need to blend or match modules from multiple Gen 2 packs.)  We were matching based on rest voltage and then bench testing swings in voltage under load, once a pack was assembled.

Preparing to go to battle over parts supply, I combed the Internet for information about Battery Boy’s operation, only to discover evidence that his process for “matching” modules was a lot more intelligent than ours.  I invited Ted for a visit and, recognizing LG as a potential partner, he shared his methods for battery testing.  Rather than argue access to salvage parts (or steal his testing procedure), the obvious choice was to buy pre-matched modules directly from him.  Though this increases the cost of the parts, it is still much less than buying a pack from the dealer and saves us the headache of trying to match modules in house (an increasingly labor intensive process).

In short, at this point we are buying packs from our competitor, with the hope that local folks will opt for the convenience of an SF location (Healdsburg is still 90 minutes north, without traffic) and the professionalism of a bona fide shop.  In keeping with our ethics, I openly admit our product (the battery modules themselves) are identical to the ones sold directly from Battery Boy.


Besides competition for Gen 2 packs, the packs themselves are only getting older.  When we first started rebuilding, Toyota was still making new Gen 2 Prius, making the supply of “fresh” packs seemingly endless.  No longer.  Gen 3 Prius have similar modules (for now; the transition to Lithium is imminent) but salvage units sell at a premium (the car is still so new).  The true supply of updated modules (Gen 2 or 3) is highly competitive (see above) and many packs (from 2004-2005 model years) have an excess of 100k or 150k miles.

In 2007/2008, the Gen 2 Prius was seemingly invincible, especially compared to the Gen 1 (Toyota’s freshman effort).  Now we’re starting to see failures of Gen 2 packs (the first was a 2005 with just over 150k miles) and a few customers have reported getting replacements at the dealer under the 10yr/150k mile warranty.  Most of our experience with Gen 2 pack failure is from taxi cabs.  Some of these die prematurely due to overheating (reference the blog on clogged fans); death by natural causes usually occurs between 200-250k miles.  But cabs are all mileage and no age.  It is unclear how long the packs will last by age (rather than use), given that the second generation of Prius is only now reaching the age (8+ years) where we started to see predictable Gen 1 failures.

At this point I have much less confidence saying Gen 2 batteries are significantly improved over Gen 1, at least in terms of battery life.  This pertains to Gen 1 owners who are hoping Gen 2 modules will last longer as rebuilds, as well as Gen 2 owners outside of warranty.


Even when buying vetted modules from Battery Boy, we encounter weak cells that diverge right away (during testing in the rebuild process or a few weeks after) and cracked modules leaking electrolyte, setting P3009.  Though the failure rate is not overwhelming, it is climbing.  The most recent jobs have required redos 50% of the time. 

LG will not pursue services with a 50% success rate.  Our east bay counterparts Art’s Automotive have never entertained rebuild packs, and I’m starting to appreciate their stance.  We’ve always presented the procedure with caveats compared to replacing with brand new, but repeated battery failures are unpalatable. 

Weak cells may be mis-categorized or simply tested improperly by Battery Boy (who processes hundreds of modules).  A rash of cracks (leaking electrolyte) was originally attributed to dropping modules and still using them (when they should have been discarded).  We are still learning best practices.

But most recently we had an electrolyte leak from a pack that had been in use for over nine months. To be clear, this is not a leak from deposits (see another blog on P3009) but a literal crack at the bottom of the plastic, leaking liquid to the metal case. Having served for nine months without issue, this kind of comeback is the most alarming, as we can’t honestly foresee such a problem during the assembly process.

The only explanation I have is that the modules become intrinsically weaker in the course of handling that takes place between sourcing from the donor car, shipping, testing, reassembling in the new pack, and installing.  Of course this is just a hypothesis based on a small sample of issues compared to the total.  But we are highly sensitive to problems as they present themselves, so we don’t miss warning signs.

Where does this leave us?

Luscious Garage no longer recommends rebuilt battery packs as an alternative for Gen 1 Prius owners looking to save money.  When presented with the latest information, our customers opt for new packs as a reliable repair.

We continue to support our past rebuilds with a one year warranty, the same as Toyota extends to its brand new packs.  All of the complications mentioned in this blog were covered under warranty.  But the potential hassle of a rebuilt pack is an essential consideration for Prius owners.  What is the cost savings of a rebuilt pack really worth? 

Someone recently emailed us a link to a rebuilding manual, now available online, for folks looking to rebuild their battery packs themselves:

Toyota Prius Hybrid Battery REBUILD

I admit I haven’t put up the $80 to see what it says.  Hopefully it’s empowering to people.  That is certainly the hope of sharing our information about the dynamics of part sources and the challenges of producing a reliable battery.  Though $2299 for a replacement pack is expensive, you know exactly what you’re getting, which has certain value the more experience we have in the battery field.

Need help with a battery problem?  Email us for an appointment….

Carolyn's avatarPosted by Carolyn Permalink Categories: Repair »


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