Featured Dome light fuse / J6 Connector / slow battery drain

Welcome to PriusChat!!

How many hours per week do you drive this vehicle?

How old is your current 12v battery?

 

how many volts does it lose overnight?

 

I’ve discussed junction connector J6 before. I wouldn’t assume that there is anything wrong with the connector or fuse; among its other functions, J6 connects the unswitched DOME and HEV circuits to loads, such as the body ECU, door control receiver, and hybrid vehicle control ECU, that all need power when the car is off.

There aren’t actually that many loads. In the System Circuit pages of the Electrical Wiring Diagram (more info), J6 is shown in the diagram for every system that involves the combination meter, for example, since one of its power supply connections is from the DOME fuse, via J6.

What were the test conditions? For example, were the doors open (so the interior lights would be on), or did you have a key in the car or nearby? Have you reviewed any of the earlier threads about similar problems?

I’m not sure how you’re testing, but it wouldn’t surprise me that you’d see low resistance to ground. If the terminals were actually grounded, though, I’d expect fuses to blow.

This calculation is faulty. A current of 0.4 A (400 mA) at 12 V is 4.8 watts, no matter how long it continues.

 

Since you have the ability to measure the quiescent current flow, I suggest you look for a stuck relay in the main relay/fuse box next to the inverter, in the relay box above the engine, and in the relay/fuse box under the dashboard, driver side.

 

texas hybrid batteries

 

I’ve seen this before. There’s a switching circuit in the combo meter that draws about 300 mA from the dome circuit. It’s only supposed to draw for about 10 seconds after the car is turned off but if the switching transistor fails it will continue to draw.

I can tell from the picture that somebody worked on that board before. They either damaged something or didn’t realize the problem.

We’re aware of this possible malfunction so all meters that we sell are tested for proper current draw and shut down switching operation before going out to a customer.

I’d be happy to work with you on a repair or replacement.

Matt
TX Hybrid

 

I highly recommend Texas hybrids for the win.

On my second year of his rebuild works like a champ. Thanks Matt!

 

pleasure

 

Did you resolve this draw problem? I too have a constant parasitic draw on that circuit of 0.4A
Regards
David

 

The combo meter PC board contains a DC-DC switching power supply which provides proper voltages to the VFD (vacuum fluorescent display).

You are correct that this DC-DC converter should switch off when the car is off.

The 300mA drain should occur only when the VFD is illuminated (car in IGN or READY mode). However, something is causing this DC-DC converter to remain active at all times. It should only be switched on during times when the VFD display itself is illuminated due to the car being in "READY" or "IGN" mode.

I've been working with VFD displays throughout my lengthy career as an electronic design engineer. Starting in the 1970's they became popular in clocks, calculators, VCRs, CD players, microwave ovens and many other home stereo components and appliances. They are still widely used today.

VFD displays are actually a specialized vacuum tube. They contain a filament which must be heated in order to emit the stream of electrons which lights up the blue-green fluorescent segments inside the display. This filament does not get bright enough to glow visibly. However, power consumption of a VFD filament is 1 to 2 Watts (or a bit more) even though it isn't hot enough to glow. Because the Prius combo meter VFD display is rather large and also must be capable of getting very bright in order to be visible inside a car, its filament will have higher power consumption than VFD displays used in household devices.

My theory is this 300 mA is powering the VFD filament even though the car is off and the display isn't displaying anything. 12V x 300mA = 3.6 Watts.

This DC-DC converter generates the proper voltages to operate the VFD. As described above, the VFD filament requires 3 to 4V at roughly 600mA (2.4 Watts). A VFD also requires a -30V DC source to supply the stream of electrons which causes the fluorescent segments to glow. Current demand from the -30V source is <50mA (up to 1.5W). Max current occurs only when many of the VFD display segments are illuminated at the same time. However, the VFD filament current is constant regardless of whether any of the fluorescent segments are visibly illuminated. Therefore 2-3 Watts will still be consumed by the filament itself even when all of the fluorescent segments are off.

The DC-DC converter is located near the transformer on the lower right corner of the combo meter PC board. There are several electrolytic capacitors of the "through-hole" type located near the transformer. This section of the combo meter PC board is several inches away from the place where the well-known 220uF 16V capacitor which often fails is located. In fact the 220uF capacitor bears no relationship to this other issue of the combo meter consuming excessive 12V supply current while the car is off.

Therefore this issue needs to be addressed so that forum users who choose to repair their combo meter can end up with a repair which is fully functional.