OBDII

Toyota Prius 12V Auxiliary Battery Diagnosis and Replacement (Gen II: 2004-2009)

Posted by Amy Kong

Turned on my car one day and saw this: “Caution – The Transmission P lock mechanism is abnormal. Park your car at a flat place, and apply the parking brake completely.”

I’m thinking: “It looks pretty flat to me, buddy.”

The 12V battery (not HV battery) is failing. Here’s how to diagnose the problem and repair the issue.

** There’s also way to access a nifty hidden maintenance menu on the MFD (Multi Function Display) – See video at the bottom of this post **

Diagnosis:
Gen 2 Prius bad 12v battery – symptoms

Tutorial:
How to Replace the 12v Auxiliary Battery 2004-2009 Toyota Prius
http://priusdiy.com/tutorials/interior/12vBatteryReplacement.html

Battery:
Optima Yellowtop DS46B24R
Purchased at O’Reilly Auto Parts, price matched with Pepboys for $129.70 (Originally over $220).
This Optima battery is supposedly “exactly the same size as the OEM battery.”

My Video: My First Readings from MFD Maintenance Mode and Scanguage 2 after the 12V battery swap

Hacking my Toyota Prius – Fun with OBDII

Posted by Amy Kong

Toyota did not intend for Prius owners to perform maintenance on their own vehicle. Without a tool that can send commands to the car’s ECU/computer, standard maintenance such as changing brakes, flushing the radiator, or changing the transmission fluid cannot be done properly. As I perform my own maintenance on my car, I became interested in OBDII (On Board Diagnostics) tools and researched the difference between dealer and consumer OBDII tools. Consumer OBDII tools such as the Scanguage2 and ELM327 can only pull diagnostic codes and read data from the ECU while Dealer tools can issue commands to the ECU and even reprogram the ECU. Definately dangerous if you have no idea what you’re doing 🙂

In the video, I’m toggling my on/off the power indicator light (see top left) using Toyota Techstream TIS (dealer/mechanic software), Drew Technologies Mongoose OBDII cable, Windows XP (32-bit) virtualized on my Mac.

Gallery of Prius in Maintenance Mode and various OBDII tools