TSB (NiMH only): Reduced power when accelerating from a stop

On July 27, Toyota issued Service Bulletin T-SB-0241-17, “Reduced Power When Accelerating From a Stop,” applicable to 2016 and 2017 model year Prius cars sold in the U.S. with NiMH batteries (ZVW50), but only if, “after repeated driving on long downhill slopes,” they have either of two symptoms: a reduction in power “when accelerating from a stop, or from extremely low speeds,” or a battery monitor that “continually shows one bar.”

The countermeasure is a software update for the Hybrid Vehicle Control ECU, in which the “logic has been modified to reduce the possibility of these conditions.” With the new software, the HV ECU part number changes from 89981-47550, 89981-47551, or 89981-47552 to 89981-47553, but no parts are physically replaced. Dealers should affix an Authorized Modifications Label (00451-00001-LBL) under the hood after reflashing the ECU.

In the U.S., the update is covered by the Toyota Hybrid Vehicle System Component Warranty (96 months or 100,000 miles), but only if the symptoms in the bulletin are present and the vehicle was produced before the relevant production change, i.e., it has a VIN earlier than JTDKBRFU#H3035100 (Tsutsumi Line 1) or JTDKBRFU#H3544587 (Tsutsumi Line 2).

At this writing, the bulletin appears to be available only by subscription to techinfo.toyota.com; I’m not aware of a free source. The calibration files are also available to download there, but only with a Professional Diagnostic subscription (from $55).

Considering the real possibility of a damaged ECU if the update fails, however, I’d advise against a do-it-yourself update, unless you (a) are prepared to follow the instructions in Service Bulletin T-SB-0134-16, “Techstream ECU Flash Reprogramming Procedure,” to the letter, including the use of a genuine Mongoose or other approved vehicle interface module, plus a GR8 Battery Diagnostic Station to maintain the 13.5-volt power supply, and (b) could shrug off the cost of replacing the HV ECU (list price $312.50) if something goes wrong.

For reference, here are the old and new calibration IDs (software version numbers) listed in the bulletin:

	Previous MAIN Calibration	Previous SUB Calibration	New MAIN Calibration	New SUB Calibration
1	899834751000	899854702000	899834751300	899854702200
2	899834760000	899854702000	899834751300	899854702200
3	899834751100	899854702100	899834751300	899854702200
4	899834751200	899854702100	899834751300	899854702200
5	899834760100	899854702100	899834751300	899854702200
6	899834760200	899854702100	899834751300	899854702200
7	899834734000	899854701000	899834734300	899854701200
8	899834734100	899854701100	899834734300	899854701200
9	899834734200	899854701100	899834734300	899854701200
10	899834757000	899854707000	899834734300	899854701200
11	899834757100	899854707100	899834734300	899854701200
12	899834757200	899854707100	899834734300	899854701200

 

In principle, yes; if you’ve never noticed the problem, there is no need for the update.

In practice, probably not: if you visit a Toyota dealer and say something like, “After descending the Angeles Crest Highway [or whatever long, steep grade might be well-known in your area], the car wouldn’t accelerate very well,” and mention the bulletin number, I wouldn’t expect them to pass up the chance to satisfy you and bill Toyota for 0.4 hours of warranty labor by doing the update, especially if you’re also paying them for other maintenance in the same visit.

 

The bulletin I described above is only for the U.S. market. I checked the list of Prius (ZVW50) technical service bulletins on toyota-tech.eu and didn’t see anything listed with a similar title.

This is only a service bulletin, not a campaign or recall, so dealers are expected to apply the countermeasure only after a vehicle is presented for repair of the condition described in the bulletin. Toyota and its dealers are unlikely to contact owners proactively about service bulletins; indeed, Toyota Warranty Policy 5.21, “Warranty Solicitation,” prohibits dealers in the U.S. from making such contacts, unless there is a campaign or recall.

There isn’t one listed in the bulletin.

 

Toyota revised the bulletin described in this thread. It now applies to model years 2016–2019, but still only to models with a Ni-MH battery. See T-SB-0241-17 Rev1, “Reduced Power When Accelerating From a Stop” (PDF), October 28, 2019. The original bulletin from 2017 (PDF), now obsolete, is also on NHTSA’s website.

 

For model years 2016 and later, the Four grade has a Li-ion battery. You can confirm this by looking at the certification label inside the left front door (the driver’s door, on U.S. vehicles), which will have a model code that begins with with “ZVW51.”