I've had the check hybrid system light on for awhile now. Cruise control doesn't work while this is active. The car behaves normal otherwise. Sometimes AC isn't great when not moving, but other then that all is well. I took it to Toyota for them to diagnose since my regular mechanic troubleshooted as far as he could. Dealership said I need to replace the PCM and after that possibly the DC to DC converter. They wanted me to pay $2,000 for the PCM and if that didn't fix it which they thought it might not then replace the DC to DC converter which would be $4,000 plus labor.

I replaced the PCM on my own with no luck, problem was still there the same. So I replaced the DC to DC Converter myself, again no change. I need some guidance. I'm thinking it has to be a wiring issue but I have no clue what I should be checking or how. Can someone please help me! Or if you live not too far from South Jersey I could drive for help. I'm lost and I'm not in a position to just replace the vehicle and trading it with the light likely will hurt me big time. I'd rather not get rid of the car.

 

From the service manuals:

P0A09-591:

Hybrid vehicle converter voltage switching (VLO) signal circuit malfunction (Open or short to GND)

Trouble area:

• Wire harness or connector
• Inverter with converter assembly
• Power management control ECU

There are oscilloscope checks on A38 and I3 and resistance checks on various pins on A13 and A38. Did you conduct those?

 

I did not. I dont know where any of the connectors are or which ones to check. I saw a few things online but the pictures don't tell me exactly which plug to look at. I don't have an oscilloscope, bit I could pick one up. I have a multimeter.

Do you have any guidance on what to check and how? I followed videos to replace the DC to DC converter and the ECU I just followed what I had read.

 

Get two day access to the entire Toyota tech library for $25:

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You can download and print portions of the manual as needed.

 

i would start with checking the ground wires and the connections to the 12volt battery it self.....

depending on what state you are in it should still have some warranty left ( 10 years or 150,000 miles, ) NJ does follow the illegal Non elected, non voted C.A.R.B. federal law(s)


100% nothing wrong with the PCM and dc-dc I had this same code yesterday and fixed it by getting a new 12v battery. we had crazy weather hot cold hot cold hot... which suddenly failed when driving...

look at the 12v battery, how old is it? load tested? did you check the connector? checked the fuses?
basics first...

this is specific to the toyota hybrid though the problem is in the 12volt system it self
2005 Prius trouble codes P0A08 and P0A09 | PriusChat

 

I bought a cable and paid for techstream. I bought an oscilloscope, I couldn't figure out how to use and couldn't find a video to explain It well enough. I had 2 AC codes that point to a defective Hybrid Controller ECU. I'm assuming it's the 89681-06031 part I found under the dash. I haven't been able to find instructions on how to replace. Not sure if I can buy a used one and install or if there is anything else I need to do to try it. I called the dealer and they said they think it might need to be programmed but they couldn't tell me for sure. Today u had 2 extra lights that were flashing and then they went away. I also noticed the efficiency gauge on the left in the dash was showing I was in the power band when I wasn't accelerating hard and even with light braking it would show it was on full regeneration. Anyone know about replacing the hybrid ecu?