Loss of Regen Braking?

Hi ,

It is much easier to help you if you post the diagnostic codes that the car reports for why it turned those warning lights on.

People often read the codes using an old beater laptop with a USB J2534 dongle and Techstream software, though there are other ways. One way that is very quick if you don't have such a setup is to trigger a code blink-out mode with a short length of wire, and count the blinks, and report those here. You can search up many threads here on how to do that.

Without the reported problem info from the car, we'd all be guessing.

 

In your shoes? I'd take it to dealership, have them check it out, see what the trouble codes are.

I appreciate that's not directly helpful, but it's a rolling computer.

Should not cost over $100 for that.

Maybe should have asked first though: do you have anything constantly plugged into OBD port? That caused similar problems for me, in past.

 

how many miles on her? is the inverter pump working?

 

I had a scangauge constantly connected, and it was the apparent source of similar issues, dubbed communication errors by dealership. They saw sporadic loss of signal when connecting with techstream, if they wiggled the connection, and suggested I try disconnecting the SG.

Did that maybe 4 years back, and had no further problems. Seems like having a constant weight on that connector, maybe tapping it with a knee, can be problematic.

Not saying for sure, and I'm not sure if you still have something hooked up, but if so: but something to try.

 

Reading the codes is more important than clearing the codes. (Clearing makes reading them harder.) Got 'em yet?

My ScanGauge hasn't caused me any such problems, at least not since I bought it for my Gen 1 and it came with the non-Gen-1-compatible cable, and I had them send me the other one.

I did recently see comm errors resulting from a different OBD thingy that I had built using a cheap J1962 connector whose pins were unplated. It worked fine when I first made it, but after about ten years riding around in the glove box, the unplated pins got (invisibly) oxidized enough that it would cause errors just by being plugged in.

I rebuilt in on a better J1962 connector whose pins are gold plated and it causes no such problems now.

In my experience, there was nothing subtle about the effect of plugging the bad connector in. Boom, most of the dash lights including the master warning triangle, "PROBLEM" on the MID, the works. And the lights would all stay until the third drive cycle after removing the wretched thing, unless manually cleared with Techstream, which would show a flurry of Uxxxx comm errors reported by multiple ECUs. (Which is kind of what you would expect, for a comm error.)

In this case, still could turn out to be something more mundane.

 

My experience was "subtle". With SG plugged in, it would be fine for maybe a week, then out of the blue: Check Hybrid System warning, plus 2 or 3 brake and skid-control related lights, plus a strange return-to-defaults feel to the brake.

This was getting to be a regular event. Discontinued the plug-in, problem never reoccured, and that was close to 4 years back.

My guess is there was nothing wrong with the connector, but the steady weight, and maybe something a little defective in the OBD port internal connections, would eventually tip the system, upset something.

It doesn't hurt to try disconnection (if he in fact still has something constantly plugged in), see if that stops the behaviour.

 

I do, as it happens. It just gets kind of exhausting to either keep re-explaining it, or searching up the posts where I've explained it before looking for the ones where I explained it best. Sometimes I end up wondering why I'm doing it and not the person who wants the information.

Here's one with a diagram, might be handy.

Here's one where I explained the blinking in more detail. It happened to be for Gen 1, where more ECUs blinked, but the principles haven't changed.

Here's another.

Can that get you started?

None of this is secret knowledge, by the way; I know it because it's covered in the Repair Manual, and there's a PriusChat wiki page on how to hook yourself up with that. (Elektroingenieur wrote the wiki page as a way to repost it less often.)

You'll want that anyway, as having the codes by themselves isn't super enlightening; the manual is what says what they mean and how to find out what caused them.

 

I don't think the order actually matters; it's just a set of codes. It cycles around forever, so it 'starts' with whatever one you wrote down first. (I think the computer actually starts the sequence with the lowest one, but again, it doesn't really matter.) As long as you don't mix up the digits and write down 13 and 84. That doesn't happen often, because it is a longer pause in between pairs, long enough to tell the difference.

38 (a/k/a C1238) has to do with the signal from the right rear wheel speed sensor.

41 (a/k/a C1241) is listed a few pages later in the manual (making it hard to find if you look where the other ABS codes are) because it's a code that either the ABS or ECB systems can report. It has to do with low supply voltage reaching the brake circuitry. This doesn't always translate to a 12 volt battery problem; as easily it can mean a loose or corroded connector issue somewhere in the wiring harness, etc. But it doesn't hurt to go confirm the 12 volt battery has a reasonable charge. Perfection's not the standard here; voltage below 9.5 (edit: under load) is what'll set the code,

43 is a VSC code that just means "hey, there's an ABS code, go look at that."

36 is an ECB code that just means "hey, there's an ABS code, go look at that."

So it's your two ABS codes that bear looking into.

The C1238 has a thirteen-page section of troubleshooting steps in the manual so you can pin down what was causing it. (The thirteen pages cover all four codes that are like this one, for all four wheels. It's just the first few pages that are in common to all, and the last six pages that pertain to the rear wheels.) A multimeter is needed.

There's a reference to a speed sensor signal check procedure (elsewhere in the manual) to try after you have repaired or replaced something. It involves triggering a test mode, then driving a certain distance a certain speed (a big empty parking lot or empty street is good). The test mode is more sensitive than normal, so you find out if the problem is fixed or not faster than you would find out just by clearing the code and waiting for it to come back.

The C1241 has seven pages of troubleshooting info. It also has a few different three-digit "INF codes" that give you very specific details about what was detected to set the C1241 code. Sadly, you can't get the INF codes via light blinks. A reader like Techstream will get them for you.

Techstream can also unpack the "freeze frame" that was taken at the instant the code was set and records all of the sensor readings at that instant. For instance, it will have the voltage measurements at several places in the brake system at that time. That can also be very helpful in working out why the code was set.

 

For whatever reason (maybe because it wouldn't be simple), the repair manual doesn't give anything like an OK/NG resistance test for a wheel speed sensor. Instead, it approaches the problem by giving continuity/isolation specs for the wire harnesses (starting with the short stub one at the rear that you exhumed the inside end of, and then from there forward to the brake ECU), and a test that the brake ECU is correctly putting 5.7 to 14 volts on the RR+ side of the circuit. The steps end up at replacing the wheel bearing/sensor as the last resort, if you haven't found the problem anywhere else.