Gen 1 Turtle mode-warm weather

Was car parked in the sun? With windows closed? Did turtle disappear after you drove it awhile, with A/C on?

 

Advice I've read, and it makes sense to me, is to run A/C in hot weather (fairly often in FL, I suspect), as air intake for HV cooling fan is on rear shelf, and cooler cabin temp air will make the HV happier.

 

Are you running on the original/OEM replacement/rebuilt traction battery and what mileage?
Not sure at what point you measured the module voltages but here's what I've found…If there's a difference between module voltages greater than 0.3v (0.69 in your case) the car engages turtle mode which allows it to charge all modules over 100% i.e. perform a top balance. When it does this the traction battery fan will be at full speed because the modules will get not a little warm. This is (or was) considered quite normal behaviour for my model and probably why there's no code. However, if it has to do this on more than 3 occasions it'll likely throw up the red triangle because one (or more) modules is failing and cannot be brought back into line with the rest. That's when you will get a few codes. Depending on how serious the ECU deems it to be will determine whether or not the car will allow you to drive it any further…ask me how I know this
Regards, Jay

 

I have little confidence that the turtle light and top balancing are related.

I caught my gen 1 doing a top balancing cycle several times (those posts are around here somewhere). The turtle light was not involved any of those times.

I did see the turtle light one summer day when taking a steep twisty road at very low speed. It seemed to be a warning that the car was putting a temporary limit on battery current because of extreme battery temperature or very low charge. Pretty much as the owners' manual explains it.

 

@ChapmanF

Understandably, for simplicity, the owners manual does not go into all possible technical reasons why a turtle might get set. It describes the turtle to drivers mainly as a battery temperature/reduced power indicator because that’s a clear message for drivers to drive cautiously. It focuses on temperature extremes and “drive without hard acceleration.”

However, as you know, the hybrid control system monitors many signals: pack voltage, module voltages (for imbalance), pack temperature sensors, cooling/fan status, inverter status, HV isolation, and current limits. If any of those conditions imply the pack can’t safely meet demanded power, the ECU will reduce output — and in that situation the turtle must be set to provide a visible driver warning for safety. A severe module imbalance, even when pack temperature is registering normal, is a legitimate reason for the ECU to limit power.

It has been suggested that Toyota only mentions pack imbalance and decreased power in 'R' to protect themselves from disgruntled purchasers immediately discovering that it might do that in 'D' while driving on the freeway—especially since they could be fairly confident it wouldn't be likely to happen until the pack had done many tens of thousands of miles.

 

You've listed a number of things there I do know. However, your assumption that the turtle light is controlled as you think it must be, rather than as Toyota documents, is not among the things that I know.

Gen 1 was the last Prius generation to be equipped with a turtle light. Later generations monitor for the same conditions you've listed above, and do have diagnostic codes and a master warning light to go with them, just as gen 1 did. But the turtle light was dropped, so its supposed necessity as "a visible driver warning for safety" is not especially strong evidence for your assumption that Toyota hedged the documentation.

 

@ChapmanF

On the other hand…by redesigning the system significantly between Gen 1 & Gen 2, Toyota removed the need for the turtle by ensuring that power output remained consistent and protected the HV battery even under fault conditions.

Gen 1 used a 273.6 V pack operated across a relatively wide SOC window of about 20–80%. This broader cycling increased the likelihood of module imbalance under load and potentially increased failure rates. Gen 2 however reduced the pack to 201.6 V, introduced improved NiMH modules with lower internal resistance and better cooling, and—most importantly—restricted operation to roughly 40–80% SOC. By avoiding deep discharge the ECU significantly reduced module stress and imbalances, so the need for drastic power limiting was minimised. As a result, power reduction in Gen 2 is smoother and less frequent, and instead of a dedicated turtle, the driver receives a generic 'Check Hybrid System' or MIL if various thresholds are crossed. So, the same protections persist, but the redesign and more robust NiMh pack made the turtle unnecessary.

 

I've quoted your post with colors added, as the least wordy approach to your way of mixing things that are definitely true and things you've assumed but not shown to be true and things you've assumed to be true that aren't as if they all had equal weight.

In choosing between orange and red I have given benefit of doubt. I do not recall my own gen 1 routinely going below 40% SoC any more than later gens do, and I don't think I've seen any documentation of gen 1 routinely using a wider SoC range, or of that range being narrowed for gen 2, but I leave open the possibility that you could provide some.

Your post #5 claimed there's a turtle "mode which allows it to charge all modules over 100% i.e. perform a top balance" but those aren't directly connected; gen 1 top-balance cycles that have been observed and reported on PriusChat usually are unaccompanied by the turtle light. If such a cycle happens to raise the battery temperature enough, it could happen to also light the turtle for that reason (battery temperature is a documented reason for the light to come on). I never saw a balance cycle do that in my own gen 1 but I won't insist it can't happen.

You responded to the owners' manual documentation of what lights the turtle light by further assuming that "for simplicity, the owners manual does not go into all possible technical reasons why a turtle might get set. It describes the turtle to drivers mainly as a battery temperature/reduced power indicator because that’s a clear message for drivers."

The same description, though, is found in the 2001 New Car Features manual, which is service documentation for technical audiences, the source of much of the technical detail known about the car.



That's taken from page 32. Page 26 also contains a version of the explanation with "This is not [a] malfunction. This condition may be corrected by avoiding sudden acceleration/deceleration, after which the light will go out."

Most recently, you've further assumed that, in gen 2, "instead of a dedicated turtle, the driver receives a generic 'Check Hybrid System' or MIL if various thresholds are crossed."

That assumption, though, conflates two things. The check hybrid system and diagnostic codes will be given in gen 2 when battery voltage / IR / charge thresholds are crossed, just as they were given in gen 1 when those thresholds were crossed. (The exact diagnostic codes are different; gen 1 assigned codes in the manufacturer-defined P3 range, while by the time of gen 2 there were SAE-standard P0 codes with the right meanings.)

The turtle light in gen 1 simply indicated a temperature-extreme or low-charge transient situation—not considered a malfunction—during which the controls would limit output power. The gen 2 2004 New Car Features manual describes the same limiting of output power under the same conditions (page TH-46, "System Monitoring Control", second bullet). It's also not considered a malfunction, and lasts only until the extreme temperature or low SoC passes; there just isn't a turtle light for it anymore.

Your earlier idea that, under your assumed conditions, "the turtle must be set to provide a visible driver warning for safety", seems to be one the Toyota engineers have, after experience with gen 1, decided they don't agree with. The car still limits output under the same conditions, but no longer also lights a light to say so.

I don't find a published explanation of why they no longer thought the light necessary. Experience may have shown that drivers are already good at noticing when the car responds less powerfully to their foot, and making them at the same time identify a new yellow light on the dash was more distracting than helpful.