Thoughts on diagnosing a hybrid car... in practice.

There is a little bit of a story here. For thousands of years stories were how people learned the knowledge their people had accumulated over the years. We have lost that in this day and age where we have unlimited data at our finger tips. It can be a huge benefit but it can weigh you down. Lets see if we can find some truth hidden in the mass of data about diagnostics.

Enter a new customer with a Prius that does not move under its own power with a "service hybrid system" message on the dash. Other then that message the lights on the dash reflect exactly what happens when you hit the start button without stepping on the brake pedal. They called me since they heard we were good with Toyota's. You wont find someone who loves Toyota's as much as me although I will happily admit that I own vehicles from other manufacturers (when they do it right). Catch 22... the truth never would be...

This was a no start after all. The vehicle would not move under its own power no matter what key you used nor basic's missed. Luckily the customer had AAA so the car was towed to the shop to see what is going on. Having just started my vehicle locksmithing services I asked her to send both keys. I had seen several recent videos about issues with smart keys needing to be replace by locksmiths to make me biased enough to hope this was one such issue that would make me shine. Not only that but they loved their Toyota which always brings a tear to my eye...

Ultimately the issue was not a dead 12V battery or a key issue as those were quickly eliminated through simply having access to the car. Code scan revealed the following: P3004, P0A08, and a couple C#### codes for the regenerative braking and hybrid battery. The key here is what to focus on first. You cannot just focus on the C#### you need to take into account the P#### codes first. Attempting to clear the codes showed that the P3004 was a hard fault where as the other ones disappeared (for now). Codes that will not clear are a great place to start diagnostics. I checked the car screen on the radio and saw the battery was 80 percent charged which is another good sign that there is no issue with the battery itself.

I plugged in the Snap On Zeus as I had recently had a Snap On Diagnostic trainer show us some of the newer features of their flagship system and ran through a few quick tests before I jumped into their new "Diagnose" button that is next to every code in the scan. The inverter pump is not the easiest to access so I decided to grab onto one of the hoses that run from it while I cycled it on and off with the diagnostic computer. Obviously it still moves fluid and in this case not related to the problem we were having. The "Diagnose" button next to the P3004 brought up what I like to call a Point of Sale screen that has common fixes graphed & listed right at the top of the screen. The fixes were not what grabbed my attention: it was the TSB button with the exclamation point. I followed through the TSB relating to this issue and the diagnostic flow chart till it got to the point: replace inverter.

There is an order of importance and critical thinking that needs to go into diagnosing hybrid systems. I ran the issue, codes and what I found by someone I know who has strong diagnostic skills and let him check the car out himself. We had a disagreement as to whether or not we should be replacing the inverter even though he clearly admitted he did not have much diagnostic experience with Toyota hybrids. We decided to go ahead and replace the inverter even though we agreed to disagree on the cause as well as the inverter pump as it is easy to do with the inverter out of the way. My friend was paying more attention then I was to the C#### codes even though they were not hard codes.

On a Prius the Inverter is what sits between the motor/generator in the transmission and the hybrid battery... of course it would have regenerative codes and hybrid battery codes if there was an issue with the inverter itself. I have owned a couple of these with bad batteries and the screen that shows their level of charge in car always show them as depleted. That one simple graphic that is displayed all the time made all the difference in the world when it came to what is actually going on with the car.

In the end it was the inverter causing all the problems which was replaced with a used unit as new ones were almost $4,000 from the dealer (dealer having admitted to never having sold one). Diagnostic trouble codes can lead you down the wrong path especially if you do not prioritize their importance or use your brain to rule out their importance. Everyday I plug a diagnostic computer in and do a code scan on a car that has 20+ codes stored most of which are related to initialization, love voltage, tpms, radio, hvac, that may or may not indicate there is actually a problem. Certainly a TPMS issue related to why the check engine light is on... so far :)

Just food for thought.