2003 Dashboard, Horn, MFD Screen Problems P3002 & P1636

1. What is the voltage across the 12V battery when IG-OFF now?
2. If below 12.4V, first fully-charge the battery.
3. When you can make the Prius READY, what is the voltage across the 12V battery?
4. If less than 13.8V, check the DC/DC 100A fuse as that may be open.
5. I suggest you obtain and download the electrical wiring diagram at techinfo.toyota.com so that you can study the diagram and figure out why the dashboard electrical systems that don't get power at IG-ON will get power when READY. You probably have more blown fuses or perhaps a failed relay.

 

Hi Francis,

1. No, the DC/DC fuse is going to be located up in the engine compartment, perhaps in the relay/fuse box near the inverter.
2. Your 12V battery needs to be fully-charged now. Use a real battery charger.
3. You need a 12V source to energize the relay coil, and an ohmmeter to measure resistance across the switched terminals. The resistance should not exceed 0.5 ohm after you account for resistance in the ohmmeter's test leads.

 

Wow, this sounds like missing power to me as well. There are multiple problems. I would start with the dash power (because that's the most obvious "no power" indicator). But thats me, there is always more than one way to skin a cat.

 

Its really so hard to tell. I see no harm in replacing the HV ECU if you have a known good one laying around (which I'm betting you do). The no dash problem doesn't appear to be intermittent to me, it appears that power is consistently lost after the car is operated. What I would do is get it to the loss of power and then troubleshoot from there (of course thats easy to say from here).

 

"No power" is a separate issue. The hybrid vehicle ECU will not affect this.

You need to study the electrical wiring diagram that relates to one of the dashboard items that does not get power. It is certainly possible that one fuse is supposed to provide power during IG-ON while another provides power when READY.

If that is beyond you, then you should seek professional help for this issue.

It is certainly possible that if you figure out the power problems, then the hybrid vehicle ECU will work just fine. An ECU is the last thing you should change, not the first - unless you know the ECU was subject to damage - for example, if the passenger footwell area was flooded.

 

You need to download the repair manual info, as I previously suggested. There are many fuses and relays that are involved in providing power when the car is IG-ON.

 

I am probably completely off base here,but it sounds like your HV ecu is toast.. I do not know if that would cause your other malfunctions or not.. Almost reminds me of an anti theft problem...

 

With any electronic system (like the Prius), if you are aware of any power supply issues, that is the first thing that you have to take care of. Only after you have correct and stable power, then you would address whatever other issues remain.

It makes absolutely no sense to be replacing an ECU for communications issues, when you know that some systems are not receiving power at IG-ON. First, get all systems to power up at IG-ON. Then if the hybrid vehicle ECU still is logged as not communicating with the other ECUs, it would be reasonable to replace it.

I recognize it may not be easy to resolve the power issues, but that really must be done first.

 

Well, since your OP says you can make the Prius READY and have actually driven the car around, I don't think that anti-theft is an issue. If you could not put the Prius into any mode besides IG-OFF, then the immobilizer ECU might be a concern.

 

The thing about this car is that we know for sure it's had electrical problems (witness the three fuses you replaced, they didn't blow for no reason) and we know for sure it's had electrical mods (as you observed about the roof harness) ... not necessarily in that order. Have you had much of a look up under the dash just to see what's in there?

I agree with Patrick that it only makes sense to start with the wiring diagrams, pin down what you're really looking for, and systematically track it down. For example, a number of the things behaving weirdly are controlled by the Body ECU. Have you checked it for codes yet? A ScanGauge can't do it; Techstream can, or the Tc-to-CG jumper and counting door-light blinks. But I'd add that it wouldn't surprise me if you get the diagram, learn from it what all components are supposed to be where, and then you look and find some box that wasn't even mentioned, that turns out to be Joe's Fantastical Automatic Door Opener, Shift Handle Heater, and Bluetooth Windshield Wiper Control, perhaps expertly installed by Joe himself as a personal favor to the DPO ... in which case there might be a limit to how helpful advice from the rest of us, who might not even have a JFADOSHHBWWC, could turn out to be.

-Chap

 

Yes, you should be able to download the electrical wiring diagram for the normal $15 subscriber fee.

You'll also be able to identify where the various ECUs are located when you have access to the repair manual.

Suppose the MFD is one of the units that does not get power at ACC-ON but gets it when READY. The wiring diagram would point you to the 15A DOME fuse.

 

That's a trick question, right? WITHOUT having the wiring diagram, I would start by ... getting the wiring diagram. I spend enough hours of my life reverse-engineering crappily documented stuff. If you're lucky enough to own something as well and thoroughly explained as your Prius, it only makes sense to take advantage of all the work they put into making it clear for you.

-Chap

 

IF you can save the files as .pdf then they will be available on your computer as long as your hard disk does not crash.