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2023 Prius Z – System Malfunction Contact Dealer

After enjoying the last 10 years with my 2015 ZR Corolla, it was time to save the environment and go hybrid!

Of course, I can never have nice things. Sure, it's got a little bit of damage to the front-left wheel arch... but the real issue was to come. Driving it home from Canberra to Melbourne saw it throw up an error (System Malfunction Visit Your Dealer) on the dashboard preventing me from seeing the power system status diagram. It also threw out most of the lane functions... but adaptive cruise still worked perfectly.

A lot of research was done... and a new auxilliary battery was installed, but the problem persisted. It was noticed, after the battery change, that the error pissed off for a while and came back 30 minutes down the track. I considered taking it to a local Toyota dealership here in Melbourne, but decided I could try and sort it out myself. So... first step... ODBII Bluetooth Reader and App.

Crap photo, but that bit top-left is the steering column cover, and the ODBII reader is in the ODBII socket... so yeah, it's to the lower-right of the steering column, down past the bonnet (hood?) latch. With this installed, I followed the steps of the associated Android App:

Actually, I lie... I first had everything ticked... but realised the errors were only coming under the LKA/LDA node, so the shot above shows just that ticked... made it much faster when re-running. But yeah, let's zoom in on that error...

So, it's C1A77(96) - LKA/LDA - Error "Show warning to user". That's not CIA, it's C1A and that initially lead me down a "there's nothing on the internet" rabbit hole. After simply tapping the link, as it says it'll search the internet, I came across this first link from a (Russian?) tech note from Toyota?

Code	Detection Item	DTC Detection Condition	Trouble Area
C1A7796	Steering Touch Sensor Component Internal Failure	When all of the following conditions are met: The vehicle speed is 5 km/h (4 mph) or more. The lane control system is on. The lane departure alert is set to steering vibrator. A touch sensor malfunction signal from the steering vibration and heater ECU (steering wheel assembly) is detected by the driving support ECU assembly for 5 seconds or more.	Steering vibration and heater ECU (Steering wheel assembly)

So, it's an issue with the ECU inside the steering wheel. The what? My steering wheel has its own digital brain? And it's having an issue with the pressure sensor in the steering wheel? That's interesting, because prior to the malfunction it knows perfectly-well if I have my hands on the wheel (or not) and happily throws the usual "put your goshdarn hands back on the goshdarn wheel or I'll make you drive by yourself"

Anyway... so... I need a new ECU for my steering wheel? sure!

Officially, it's part #1 in that diagram... and it turns out you need to pull the entire wheel apart when you want to install it. Just for fun, I popped open my steering wheel to find out what unit was installed. I wanted to compare model numbers with the part I needed to buy:

I do note that this unit number 864A1-47030 has been superseded by 864A1-47031. Does this mean I have the buggy old version that throws random errors? I went ahead and purchased the new item from YoshiParts and waited for it to arrive.

In the meantime, I scoured the web for other people having the same issues. It turns out that are a few blog posts from owners in Japan noting a similar issue. Supposedly they were told to pop the Steering Heater fuse for 90 seconds and the error should disappear. This should cut the 12v to the steering ECU and reset any error conditions. I'll note that this didn't work for me! Other's have mentioned that they received a whole new steering wheel from warranty and the problem disappeared.

Replacing the Steering Wheel ECU

The part arrived and looked brand new! This came as a great relief as I had no idea what to expect from YoshiParts. Officially I can totally vouch for them on price, service and super-quick postage!

I disconnected the auxilliary battery in the boot and let the car sit for 15 minutes. This is to prevent the Air Bag from deploying whilst we muck around with it.

First step, you'll actually need to pop off the airbag/horn unit. This is held down by three spring-loaded pins which are released by metal clips accessible on the left, bottom and right sides of the steering wheel. In fact, if you look up above where I show the model number fo the ECU, you can see the thin chrome clips. You'll need to press against these to release each of the three pins of the airbag/horn unit.

The first one to attack should be the bottom one. It's accessed through a tiny hole on the right-side of the underneath of the steering wheel. You'll need a long metal pole... be that an allen key, or a flat-head screwdriver and you'll want to find the hole on the under-side of the steering wheel and press the tool into it. After around 30mm, as long as you're running the tool as if it's aiming towards the driver, you'll hit a metal spring of which you can compress. Once you've compressed it enough, the horn button component will "pop up" at the bottom.

The hole is shown above, as seen from the underside of the steering wheel. Below you can see the end of a torx screwdriver pushing up the spring clip from below. This is the goal! Just close your eyes and gently apply pressure until you find the spring.

Once it's up, you then need to do the same via the left and right access panels either side of the column next to the stalks. Use your fingernail or a plastic utensil to remove them.

Shown above is the left side of the steering wheel with the cover still in place. You can see where to shove a tool in to pop the cover off. Once off, you can shine a torch in there to see the metal/chrome springs.

Above is cheating as the steering wheel is a spare which I accidently bought, thinking it might fix the issue. But you can see how easy the side parts are to press in. You can even use your finger!

With the three spring-clips undone, you can flip the horn/airbag unit over and unclip the airbag connector. You'll need to slide in a plastic utensil to lift the orange 'cap' from the yellow body. It only needs to lift 1-2mm. Once it's raised, you can then pull the whole plug out of the unit. You then need a tiny screwdriver to slide into both the plastic retension clip and the horn spade clip to slide them off. As with everything Toyota, there's a method to it all and NO FORCE IS REQUIRED. If you're finding it difficult then you're doing it wrong! You can now put the horn/airbag unit to the side.

I didn't take a photo, but there are two plugs to unclip (top and bottom) and then the huge 10mm allen-key socket to deal with in the middle. I had to buy a breaker bar to get it undone!

Once undone, the bolt comes out and the steering wheel can be removed. I've heard it should be on hard, but mine literally slid off.

I removed the housing...

And replaced the ECU. Everything went back in the car and settings were reset for all driving assitance packages. Before-long, bang... System Malfunctionnnnnnnnnnnnnnnnn...

Disabling LDA as a 'fix'...

Even though I'm sure I'd tried this prior to replacing the Steering ECU, I found that disabling LDA stopped the error from appearing.

This aligns with the web page at the start indicating that a condition for the error is that LDA is active and that the warning type is set to vibration. The car continued to function, but with a large orange warning on the dash that LDA was turned off:

And, I mean... I could deal with that. I drove to Canberra and back with everything working nicely, except that LDA. I don't know if I even want LDA to be active? I then stumbled across this Reddit thread titled 'Steering wheel assembly touch sensor needs replacement.' and realised I had one (or two) more options up my sleeve. I could still replace the entire steering wheel, in case it was an issue with the touch sensor... or replace the "spiral cable" in case that had gone faulty. In fact, the other user on that Reddit post was waiting on a spiral cable replacement as we chatted and I decided that was my next step.

Looking at the service manual also confirmed this...

And the fix?

Riiight... Hah.. replace everything from left to right... but actually, it only reckons to replace the steering wheel assembly? What about that wretched spiral cable?

Clock Cable / Spiral Cable

This was actually hard to find on YoshiParts! It's buried in Switch & Relay & Computer on this page and listed as part number 84306.

I only bought the spiral cable, and not the steering position sensor... and it seems I accidently did the right thing! It turns out the steering position sensor contains a security key that needs to be programmed into the main vehicle ECU if you change it! So yeah, although the steering sensor and spiral cable are massively intertwined, you really only want to replace the spiral cable if you do this!

And yeah, replacing the cable was NOT stress-free. I did the same tear-down as above to get to the cable... further removing the steering column housing. This requires three screws to be removed (don't forget the one underneath!)

Once the housing is off, you can remove the sensor + cable by unclipping it at 12-oclock where it connects to the steering column.

These photos are really useless... but there's only one clip top-center holding the unit to the cluster. Once it's off, you can remove and replace the spiral cable from the steering sensor.

One Note on removal: There are four cables to unplug along the bottom. The steering sensor has slack on its cable which can be unclipped, so do that first. Finally the airbag plug needs to be unclipped by sliding a tool down the front of it's plug. Slide the tool into the slot at the socket-end of the plug, not the wire-end! Once you've inserted the tool as far as it'll go, simply slide the plug away from the socket. Again, there will be no need for force! The main goal is that you should NOT slide the tool in from the 'wire side' of the plug.

At this point, the documentation points out that you must not change the angle of the steering sensor when changing the cable. The sensor must stay at position 0 and this can be achieved by locking it with the included locking pin.

So yeah, above, rotate the existing cable until the pin can be installed. Once locked on, unclip the 6 clips around the sensor to detach the cable. Then simply clip the new cable straight on top! No issues really! I have no idea how one would actually manage to set the steering sensor to anything other than 0 degrees...as it's totally locked to the sprial cable. You'd have to actually rotate it a full 180 or -180 to be able to clip it together and you'd sure know if you've done that?

Either way, the car was put back together with this new spiral cable and, 2 hours of driving later... NO ERRORS!

Moral of the story? Buy a car under warranty that was released in your country. But damn, I love this car!