Prius 2nd Gen – Repairing the Multi-function Display

I’m going to start this page by giving credit where credit is due: Hobbit did the initial investigation of the 2004-2005 Prius Multi Function Display (MFD) communication failure issue, and everything I’ve done so far has been built on the work he has shared on his web site.

Please don’t email or call to ask if you can send us your MFD for repair:
1. We don’t have a test bench set up to simulate a Prius, so we need to have the car here for testing.
2. We aren’t set up as a mail order repair service, and dealing with emails & shipping would be a pain.
3. We have may not have perfected the repair procedure yet.

This is the story of an MFD that is in for it’s second repair. We fixed it once, but it only worked for a month. Since the MFD is a $4000 part, it’s probably worth spending some time to determine whether a reliable repair is possible, so we gave it another go. I attempted to repair a damaged solder connection using a reflow station on the first try. This time I’ve resoldered the damage using a soldering iron, and I also by-passed the suspect area with “green wire”.

Warning: Even though there is only 12V going into the MFD, LCDs create very high voltage using a step up transformer. This is the story of what I did, not instructions for you to follow step by step. If you kill or maim yourself, don’t blame me or Art’s Automotive.

The symptoms for a failed Prius or Highlander MFD are:

"audio off" displayed on Prius multi-display screen

“AUDIO OFF”, even when the radio is playing

"Check the connection of the air conditioner" displayed on Prius multi-display screen

A “Check the connection of the air conditioner” message

Prius multi-display screen in power flow mode with no indications of power flow showing

There will also be no information on battery state of charge or power flow. If the vehicle has navigation, there will also be problems with connecting to the navigation unit.

Prius multi-display LAN monitor screen showing no connection to network

The LAN monitor says pretty much the same thing. The EMV (MFD) now says CHEK (which means there should be a code stored), but I couldn’t get it to give up any codes while it was broken. Maybe I was just being too impatient. The MFD was moving very slowly. It seemed to be spending most of its cycles trying to establish communication, and was very slow to respond to user inpu

"System Check Mode" displayed on screen. No connection to audio h/u and g/w

When you enter the System Check Mode (press & hold the INFO button on the side of the MFD & turn the headlight switch to the parking light position three times in a row, starting & ending in the OFF position), you’ll see a NCON (No Connection) warning for the AUDIO H/U as well as G/W.

The AUDIO H/U is the stereo.

G/W stands for Gateway. The Gateway ECU is the computer that allows the 3 busses (AVC, BEAN, & CAN) to talk together.

EMV is OK. What’s the EMV? It’s the MFD. Why not just call it MFD instead? I have no idea.

Basically, this means the MFD can talk to itself, but not to anyone else.

In the Vehicle Signal Check Mode does not rely on information from the bus. (The bus is a two wire data path between control units). The MFD monitors these items directly.

IG is “Ready”.
PKB is the parking brake.
TAIL is the headlight switch position.
ADIM/TCAN is the MFD dim/bright status (based on the headlight switch position it seems).

Prius display showing "Vehicle signal check mode" and values for battery, ignition, parking brake, speed, tail light, and brightness

Since the headlight switch is used to enter diagnostic mode, its position must be monitored without using the bus.

The speed is likely used for function lockout based on vehicle speed. So if you are looking to hack this, so you can drive, dial, & crash, this is probably a good place to start.

Why the parking brake? I’m not sure. I do know that Toyota locks out some scanner utilities (like brake bleeding) if the parking brake is not set. So I’d guess that the PKB signal is responsible for some sort of lockout.

Anyway, all of the stand alone MFD functions seem fine. The problem is only with its connection to other control units.

Removing Prius trim panel on dashboard

Time to yank it out. The Prius has a well designed dash. My handy KTC plastic pry bar is all that’s needed to remove all of the covers. You could use a sturdy tongue depressor, a taped screwdriver, or whatever.

Prius dash disassembly in progress

Here I have the covers removed. Well, removed enough.

removing toyota multi-display mounting bolts

The multi-display is held in place with only two bolts. There are also some retention clips, but they’ll release if you just pull straight back.

back-probing Toyota dash display connectors

First I check the resistance on the AVC bus. The terminating resistor for the AVC bus is in the stereo. An open would indicate a break in the wires to the stereo, or an open resistor in the stereo. Without the terminating resistor, the data signal gets big and sloppy. The control units will talk and listen, but have trouble hearing what’s being said, and may not be able to communicate at all. The resistance should be about 60 ohms because each resistor is about 120 ohms and they’re wired in parallel.

ohmmeter reading 68.3 ohms

68 ohms. Close enough.

disassembled prius multi-display on a office desk

This is about as disassembled as it needs to get. Since this is our second attempt, I’m a lot more thorough in my checking this time. Last time I looked for a broken solder where Hobbit said it might be, found it, and fixed it.

This time I spent some time verifying where the bus goes with an ohm meter. This turns out to be a little frustrating. 1) because of disappearing traces, and 2) because the board is coated with something that makes is hard to get a good connection with the probe tip.

Luckily Hobbit’s previous work makes it easy for me to “cheat”. It’s a whole lot easier to test when you have a pretty good idea what the eventual answer is going to be.

Square wave signals displayed on an oscilloscope

Lotsa squiggly lines. Somebody’s talking on the network.

Back-probing display connector

Next I hook up a scope. What will I be able to tell from this test? Not a whole lot. Mainly that data is being sent on the bus, but I can’t make sense of the 1s & 0s, so I won’t know what it means

Small connector on circuit board

The connectors are very small & delicate. If you just tug on the plastic connector, like you would in the normal sized world, you may break all of the solder joints where it mounts to the board. A better way is to gently insert a small screwdriver into the connector joint and twist. That way the force is applied to the plastic connectors, not the solder joints or wires. I found this out the hard way while fixing one of our LCD monitors here at the shop. I had to go back in to fix the problem I created after fixing the problem it originally had.

Prius display repair on cluttered desk

Time to tear it up. This is my third MFD disassembly, so it’s pretty easy now. I know were every connector & screw goes. The first couple times my desk looked like an operating theater with bags & bins & labels. Now I’m getting comfortable and just lay it on top of all the work that has piled up on my desk while I’ve been working on the Prius. Hopefully OSHA doesn’t notice my open can of V8 🙂

Disassembled toyota display with test wires added.

Now I’ve got one red wire & one white wire coming from pins 60 & 58 on the big board connector, and another red & white set coming from TP47 & TP48 on the little board. I’ll be able to “see” data on either side of the connector, and I should be able to tell whether the problem is between the external connector and the big board connector, or between the big board connector and TP47 & TP48 (which are sort of near the little board connector). If the connector goes open, I should see data that looks “unterminated” on the small board side and normal data on the big board side

test wires soldered into display circuit board

I’ve been practicing soldering very tiny stuff, and my skills have improved. First I soldered two leads at TP47 & TP48 on the “small board”, just like Hobbit did. Hobbit figured TP47 & TP48 were “Test Points” 47 & 48, and found that they were an easy place to access the AVC bus on the small board

circuit board and soldering station

I have a plan this time. Rather than assuming the surface mount connector is at fault, I’m going to solder test leads on either side of the connector so I can check the signal on either side of the connector, and know for sure the connector is where the break is.

3mm soldering iron tip dwarfing tiny surface mount connector terminals

Thanks to the SMD soldering tutorials on Spark Fun and some practice, I decide that I’m not afraid to try soldering my test wires right to the tiny pins.

This picture is just to give you an idea of the scale. This is a standard 3mm soldering iron tip (cold). As you can see, it’s over four pins wide.

close up of circuit board

Next I start looking for a connection spot on the “big board”. I could just backprobe the external connector, but I was hoping to find a location closer to the board to board connector. That way the connector would be better isolated during testing. Two of these tiny copper grommets go to a couple short traces the go right to the board to board connector on the other side. However, the grommets are so tiny 30 GA wire will not fit through and the coating on the board is making tinning them very difficult. After a while, I give up on this idea

Prius display repaired after resolder

I figure I may as well do the small board side of the connector with 60/40 solder while I’m at it.

Now that I’ve had time to think about it a little, I wish I had soldered wires here as well. I think that having the wire soldered to the connector leg and the pad may add a bit of support to the joint. Hobbit pointed out that the leg contact area on the new improved MFDs were much larger. Soldering the wire to the side of the leg & the pad should bolster the joint and make it stronger. Oh well. Next time. (Hopefully on a different unit!)




A couple months ago, during my first repair attempt, I had used the reflow station because it was easy for me. It’s a lot like plastic welding, and I’m pretty good at that. I had wanted to use the soldering station, but after some practice on an old motherboard, I realized I did not have the skill to work on a $4000 component yet.

This time I had more experience with a 1mm cone tip soldering iron & solder wick, so I was not worried.


I figure I may as well solder my test wires together and tape them up. They will act as an alternate route around the connector while the unit is in service. And if the does break again, they will be a way to test the MFD quickly without much disassembly. I worried a little that there may be a shielding issue, but the scope pattern looked fine.

Prius multi-display working in audio mode

But there’s nothing to test, the MFD is working perfectly. After a little shaking, smacking, vibrating, and connector tugging, I’m convinced it was probably fixed by the resoldering. I suspect reflowing the skimpy bit of existing solder does not create a lasting repair, and that adding 60/40 solder will be a better solution, but time will tell.

partially assembled prius display connected for testing

The unit is back in the car with the rear cover off. The test wire sets are dangling out the back for easy testing at the first sign of trouble.

Toyota display with trouble codes on the screen

None of the codes are current though, so I don’t bother to look them up. I imagine they have something to do with a loss of communication.

display in system check mode

Now that the MFD can talk to the stereo, the system check now says there are some AUDIO H/U codes.

Prius multi-display in diagnostic mode. Screen shows health display

After clearing codes and a test drive down our roughest local street, everything is looking good.

If you like the idea of fixing MFDs or electronic parts yourself, I’d recommend the following resources.

Hobbit’s website ( has a ton of Prius related stuff, including the original MFD repair page.

Spark Fun ( They have SMD (Surface Mount Device) soldering tutorials, kits to build for fun & practice, You Tube soldering demonstrations, etc.. They’re sort of like HeathKit from the 70s. Lots of fun, if you like that sort of thing.

Toyota’s information site ( Training courses and of course vehicle specific information.