Car Wash Caused Hybrid System Warning

Thanks Rachel for the information. One thing that always makes me nervous if the first car wash (Automatic). I have heard the door locks and unlocks when the water touched the handle area. I found it interesting that when hand washing the car, fob in pocket, the door would lock and unlock with my wet sponge midway on the drivers door. So I guess it is quite sensitive.

Hope the first time I use an Automatic Wash I don't observe any error codes....as well.

Bob

 

Just to check, is that $500 cable you bought still the only option we are aware of to access techstream?

 

Frustrating that they can charge $500 for a cable that costs $10 to manufacture...

 

I went through an automatic touchless today (3rd or 4th time in 12 weeks) with no issues, same as the other times. The only things I've touched under the hood are the dipstick and washer reservoir.

 

What magical device is this that you speak of?

 

I've been through a touchless wash several times now without an issue. I think you're on to something suspecting the fuse box getting wet.

 

Did the carwash include stuff to spray upward against the bottom
of the car, hard enough to get up on top of the transaxle? Water
could easily land on things like the MG temp sensor connectors on
the transaxle, but everything underhood is *supposed* to be sealed
with gaskets around the connector bodies and where the wires come in.
.
The MG1 [aka "generator"] resolver and temp-sensor connector appears
to be the same grey one I mention as useful to disconnect in the
block-heater page, right on top of the housing. [Oddly, the resolver
and temp-sensor connectors for MG2 are separated front and back, go
figure..]
.
I spray out my underhood area every spring to get rid of salt and
crud accumulation, mostly avoiding the visible connectors when doing
so, and that makes it easy for me to generally keep my engine
compartment cleaner than just about any other owner's I've seen.
But after I'm done I sponge out areas like the top of the engine
where water tends to accumulate in the head-cover [gen2] around the
ignitors and various connectors and anywhere else I find pooling or
remaining water that I can reach, and take the car for a good highway
run afterward so the heat and airflow dries things out the rest of
the way.
.
_H*

 

In this case, the "high" appears to mean a "high" logic level, not high temperature. It means the "circuit" level is high, or a short to B+ (+5V of the ECU).

Some attachments from the following TIS document:

HYBRID / BATTERY CONTROL: HYBRID CONTROL SYSTEM: P0A2C-247,P0A2D-249: Drive Motor "A" Temperature Sensor Circuit Low (2010 Prius)​

What's a bit weird is that water going into the connector should only be able to bring the level low, not high, according to the circuit drawing in that document. One possibility is the water spray loosened (even temporarily) the connector or the pin at the connector, briefly making it an open connection. That would do it.

 

Yes, that's what I thought, too, until I looked at the circuit more closely (attached in last post.) (OK, this maybe is more technical than we need to get, but.....) The only way that the circuit can "short to B+" (5V) is if the ground path is removed, which means that the circuit path through the sensor itself is gone (open, or at a very very high resistance). Water can only short it to ground, not short it to 5V, since if the water is touching "ground" (which it would have been), the bottom of the pull-up resistor on the ECU side ("MMT") would have been at ground potential, not 5V. But if the line is open, there is no current flow through the pull-up resistor, making the MMT line at 5V as well, which is the input to the ECU. And you would have to have that line at 5V to get the 249 code.

I agree that it's hard to imagine - but I've seen water and vibration do some very weird stuff to connections - and all it would have taken is a millisecond, since these signals are frequently read thousands of times a second by the processor. I've seen stranger. If it happens again, you might want to check that connector for integrity, including the wire-to-pin connection.

I've had mine through a similar wash (with undercarriage spray) a few times, with no problems......yet......Hopefully you won't see it again.

 

I was looking at the Gen 2 documentation for this code yesterday and I think they do mean a short to aux battery voltage - in step 2 of the diagnosis procedure, if the voltage seen at the sensor end of the wire harness is between 9 and 14V, the manual tells you to 'check for +B short'. The ECU does supply 5V to the sensor, and the sensor has a separate ground return wire, rather than using chassis ground as many other sensors and actuators do.

 

Thanks Mike,

(I promise, this is my last "horse beating" )

I agree, they probably mean a short to 12V; but in either condition for a 249 code (short to B+/12V, or open), the voltage at the MMT line would be at 5V or higher. But what would be the 12V path for this, in the case of a water short? If 12V was really being applied to the MMT line by way of a water short, it seems it would have to be at the ECU connections (not at the sensor), otherwise the chassis that the water was in contact with near the sensor would be energized to 12V! If water were present to short from some 12V line at the ECU, I would think a lot worse things would be happening and a lot more codes generated. The only other possibility I could see is a harness short if it is bundled with other wires and there were two breaches in the insulation (one for a 12V line, one for the MMT line).

The A21 connector at the ECU is inside the vehicle, on the right side of the instrument panel, obviously nowhere near the fuse box. So I don't think water intrusion at the ECU connector is the explanation. Noise on the line? Certainly is a possibility - those car washes probably generate lots of EMI. And most of the wire harnesses are not shielded (including this one).

I still think the most likely scenario is a short duration "open" on this line. But hey, I've certainly been wrong before!!

Rachael, you've discovered an interesting problem, to say the least!

 

I've been trying to figure this out too. I don't think it will work. The problem is that the $300 cable lacks the ability to adjust voltages on specific pins. This is required for reprogramming as far as I understand (documentation is tricky to come by). I read the j2534 spec and it's pretty straightforward. Originally I thought I would buy a reasonably priced cable and make the dll interface myself. Sadly, I no longer think this is possible with a cable that lacks these capabilities...