No fuse for the cargo light?

Curious. If you're measuring +12V across the lamp terminals then you have a circuit with potential. It's improbable Toyota would design a circuit that doesn't have some sort of short protection. That said, 3 ohms is too low for the bulb; that would result in a 63.5W light @ 13.8VDC, and my guess is it's a 5W bulb, so it should be reading 38 ohms. Try a new bulb.

Check through the owners manual, as it's surprisingly helpful.

Of course you won't get any codes through the OBD, that's just for the powertrain. If this car uses a communications bus for the BCM then the dealership may be able to determine something. Why Chilton's calls the BCM and ECU is misleading at the very least.

 

If the voltage drops to 0.7 volts with the lamp in place, this means there is a large resistance in series with the lamp. Toyota may have placed this resistence there to limit the current. The idea is that even if there is a dead short there can only by a few hundred milliamps in the wire. So no fuse would be required. This is not an unreasonable design for a tiny 1 or 2 watt bulb that is ony used for a few minutes a day, if even that.

I'm guessing. You have to take a few more measurements with you DMM to confirm this (or not.) Essentially you'd measure the output impedance of the light socket by plotting the voltage as a function of load. If Toyota did in fact do this then there is not much point in using an LED.

 

There is a 15 amp fuse (#13) in the under hood fuse block that is for the dome lamp circuit. The owner's manual shows it on page 405. I pulled this fuse and the cargo light did turn off. If blown, you would not have a working dome light in addition to the luggage compartment lamp. I question whether the schematic from Chilton's is correct. It would not be surprising, however, that the ECU or BCM would monitor the switch side of the lamp and use this to determine if the rear hatch is closed. When you are measuring voltage at the lamp socket, you may be seeing a high impedance input from the ECU or BCM that is monitoring the voltage on the switch side of the lamp -- not a voltage intended to power the lamp.

 

I pulled the rear compartment lamp and did some measurements myself. As stated in my prior post, there is a 15 amp fuse that powers the luggage compartment lamp, the main ECU, the audio system, and "personal lights" (includes the dome lamp). The wires to the rear compartment lamp appear to be smaller than 22 gauge wire and are not sized to handle the current required to clear (blow) a 15 amp fuse. So it does appear that damage was done to the wiring, the switch in the hatch, or the ECU (assuming the the Chilton schematic is correct). Given the post by another Prius owner who shorted around the lamp, it appears likely that the ECU is in the circuit.

When my C4 hatch is opened, there is battery voltage on the blue wire and the black wire is grounded by the hatch switch (12 volts across the lamp and it lights). With the hatch closed, battery voltage remains on the blue wire, but the black wire goes to battery voltage, indicating that the switch went open.

It may be helpful to know if the dash display still correctly reports when the hatch is closed and when it is open. Over current damage to the small wiring or the hatch switch may mess this up.

You are correct in that the dome lamp comes on whenever the rear hatch is opened. If a wiring modification must be done to fix your problem, perhaps it would be easiest to wire into the brake light right there on the corner of the car. This circuit is powered all the time (the brake switch grounds one side of the lamps, turning them on). You should add a small inline fuse to the feed to the lamp. This would work as long as the hatch switch and the wiring to it is undamaged. The lamp, however, would stay on forever if you leave the hatch open. You could add a small SPST toggle switch in the wiring to shut it off if you left the hatch open for long periods of time.

 

Hrm, I did the same thing. Think I shorted it while changing the bulb. Slightly different outcome though....any incandescent bulb does not work...but my LED bulbs will faintly light. So, its getting SOME power, but not enough to illuminate an incandescent bulb.

I checked fuse 13 and 30 under the hood, both are good.

Did you ever figure out how to fix yours?

 

The ECU has been damaged when you grounded the wiring while installing the LED. It is unfortunate that Toyota did not fuse the circuit properly, allowing the fuse to survive and the circuit board to fry. I had earlier suggested that you could wire into the brake light bulb assembly assuming that there was an always "hot" wire on the brake lamp. After going over the wiring diagrams, this is not true. The wiring to the brake lamp is only "hot" when you step on the brake. Therefore, the easiest fix is to route a wire thru an inline fuse from the 12 volt battery under the back seat to the rear compartment lamp. Sever the wire from the ECU and replace it with the 12 volt feet directly from the 12 volt battery. If you make this modification to restore the rear compartment lamp, there will be no automatic lamp shut off after 20 minutes if the hatch is left open.

 

I found a body control module for a 2010-2011 Prius on eBay for ~$150. Way less expensive than I would have expected. I realize the Prius C may have a different unit, but the price shouldn't be that much different.

I only have 450 miles on my car... and already broke it. How stupid is that design? Argh. My car goes in for a 30day/1,000 mi. service at my dealer here in a couple weeks. Its kind of a meet and greet with the service team, allows them to make sure the car is not having any immediate issues, answer questions that may have come up and set some dealer only options that can't be set by the consumer. Door locks, running lights...yadda yadda. "Hey ya know... this cargo light doesn't work back here...is there a switch someplace to turn it on?" Let them sort it out.

As a side note....did any of y'all notice the little warning sticker on the back-side cover to the cargo lamp assembly that says WARNING - unplug assembly before changing lightbulb? I did... AFTER I shorted it.

 

yeah, definitely just have the dealer deal with it for you.

i just changed mine out and noticed that sticker

 

NO! I never saw any sticker. For goodness sake, I was changing a BULB, not hotrodding the ECU!
Yesterday I spent 5 hours at the dealer plus another couple of hours on a previous visit and the Service (?) department never fixed the blown 'whatever' that shorted out from the lousy bulb holder. The service rep was too embarrassed to tell me the news, the manager explained on bended knee.
I am really pessimistic for the future of this car. On top of that they were so confused that they sent me away without any paperwork verifying my oil and tire service, plus no customary car wash. They probably did this service off the record to avoid a negative rating. I was too nice to them. I travel 20+ miles to this dealer, thinking that it is better than my local Toyota ripoff artist.
What a testimony to famous (?) Toyota engineering. Now, after my vacation trip without a trunk light, I am supposed to leave the car for a couple of days for their mechanic interns to practice on it. I'm telling you, they better have a rental car ready. They are on my bad list now. I hope a Toyota rep reads this forum to get a clue.

Change your bulbs CAREFULLY! That sounds ridiculous, doesn't it?

 

That's really crazy.... exactly why I hate messing with the electronics and prefer to work with good ole nuts and bolts.

 

It is ridiculous. I had the same thing happen to me - took the car in about 3 times for them to figure out what needed to happen - but they covered it under warranty - still. Shame on Toyota for not putting in a fuse for the light.

Always, always, always make sure to unplug the light before changing the light. I never saw the sticker either - I still don't know where it is

I've never gotten any free car washes w/ my Toyota dealer...

 

Hey all,

I've been lurking since I bought my first prius LONG before Larry David....Long before that no good son of a bitch stole my personality and made so much money from it. I digress.

This, the 2013 C-3 is my fifth Prius. I went from the Prius 'wave', to the Prius Condescending Attitude, to the Prius Flip-You middle finger. Yes, eventually I hated Prius drivers.... Except the ones I saw dangling ciggys out their driver side windows. Somehow they were my kind of people. When it comes to Prius Racial profiling I'll tell you who I hate the most. The Wealthy MILF Venice Mom's—One of whom nearly ran me over with her Prius while I was in the crosswalk. So close I smacked the hood of her car as she rolled by. I yelled. She hit her brakes, looked back at me and flipped me off. Man, what's the world come to?

This is an amazing community. I love how you guys made the news about the leaked manual. Anyway. Count me in as the Village Idiot who broke his cargo light circuit inside of 12 miles. At least I found this article, because I've gone thru the manual already looking to see if the cargo was wired to the same fuse, but how it would make little sense that there's be some faint juice to the new cargo led. what a PAIN in the BUTT it was just getting the lamp holder out. I think I sweat more than a 2 hour workout. Anyway. IS THERE A FIX? I'm making an appt. I'm not asking about being honest, as I will be—I'm just wondering how to phrase the question so the service guys get it. Do I say I "Broke the ECU installing a cargo light?"

Thanks Prius Community!

 

Well, at my 15k service at a NEW DEALER, I can say that my luggage light is working again. They gave me a loaner while they spent 4 hours patching it up.
Now get this; I know that I blew the circuit by inadvertantly changing the bulb while the circuit was connected, but they claim there was a "cut wire in the driver's threshold". That is amazing that that happened at the same time that I was in the hatch area changing a bulb, when the light went out.
I believe they found the Chinese fix (priuschat.com/threads/cargo-light-fuse.110828/) because they did not include an ECU in the parts list. Anyway, they are a dealer that aims to please and I will return again.