Error code B1421

12 volt battery bad especially if original or you ever had to jumpstart the car: Do this test and report all 3 back here:

Weird stuff happening? MPGs dropping? Test The Battery | PriusChat

 

I agree. It is indeed caused by the photo cell being in the shade. Mine has this in the garage, not outside. If you clear it, you can make it come back by putting your hand over the sensor. Somebody screwed up with this DTC, to be sure.

 

Service manual says:

Just another example of over-engineering, IMHO.

 

You would need a Prius specific code reader to see that one, such as mini VCI on eBay.

 

It's a shame that there was no resolution to this.

I'm going to bump this thread with my own question as I am getting the B1421 keep coming up.

I was hoping that it was just a glitch caused by a low voltage on the 12V bus.

However, after installing a new 12V battery and then reseting the DTC, it came back immediately. From reading about the B1421, it seems that this DTC can be thrown just by having your car in the shade. Not a very brilliant design.

My question, is normal daylight on an overcast day bright enough to prevent this code been thrown? I'm thinking yes. So if this is correct, the fact that the code came back immediately after being erased, means that further investigation is warranted.

Just looking for some feedback/confirmation that I'm on the right track before continuing.

Thanks.

 

This whole thing is ignorable. It really is a very minor engineering mistake, and the only way to resolve it would be to reprogram the AC ECU. Someone decided that turning on the car in a garage was an error condition. The sensor causes the AC to run a bit colder if the dash is in the bright sun. Nothing more to it than that.

 

If your air conditioning system works properly, and DTC B1421 is the only DTC that is registering, then don't worry.

If you insist upon worrying, then place an incandescent trouble light 1 foot away from the solar sensor, clear the DTC, and see if it stays away. You need a light that will cast heat upon the solar sensor.

If the DTC goes away under that condition, then don't worry as the sensor and AC amplifier are working properly.

 

@ nh70, thanks for your reply, but you seem to just offering a stock answer that does not address the question I asked. I would hope that reading my post properly would show that I have a comprehension of the points you raised.

@ Patrick, thanks for your reply. That's what I was looking for. My question was because I'm not sure if my A/C is working properly. It seems to take a long time to respond to changing weather conditions. I notice it particularly on a trip. I just thought outside in daylight, albeit overcast, that it should not throw the code. I wanted to check this assumption before working through the physical diagnosis procedure, given the physical location of the sensor. I will try artificial lighting. I'm not worried per sae, but wanted to be sure it is not a genuine problem before dismissing it.

Thanks again for both your replies.

 

if this is an engineering error, why only on a few cars?

 

I would not characterize this as an engineering error. Any Prius parked in a garage or in dim light will log the DTC. The point of the DTC is to show that if the car is in direct sunlight and the DTC is still present, then either the solar sensor or the AC amplifier are not working.

 

Thanks all for your help.

It turns out that, in my case, the solar sensor is working fine. Today is a brighter day and when I went to clear the code, it was not there. So I covered over the sensor with a booklet sitting in the glove box and sure enough it threw a B1421. Took the the booklet away and it disappeared. So, I'm happy with that.

Still finding my feet getting around the s/w (MVCI w/ t/s). (Also still looking for good threads on that subject)

Thanks again.

 

Why does the error say (passenger side)

My solar sensor is only on the drivers side

 

i got this code too, how do it get cleared by it self?

 

Shine a bright light on the solar sensor.

 

ok i'll do that tomorrow and the code will be gone?

 

Until you stop shining the light on the sensor.