Hello from a CT Owner with Issues

Hello Forum, signed up as most of the useful information online to do with the Toyota Hybrid system came from this site.

I own a Lexus CT200 (2017 model, middle facelift). Based in the UK. 96,000 miles on it.

I'm here for help for a very specific C1202 fault. It's intermittent on and off for the last two months.

Last year I had the brake booster replaced at the Toyota dealership I bought it from. 50 weeks of zero issues so I suspect that new part was fine and fitted fine. Unfortunately they closed their door on me when I took it back and said as the warranty which the job was done under ended last summer, so did their warranty on that work...

Unlike when the brake booster went, when my fault this time is ON, I lose ABS / traction and the brake feels like it takes more effort. But cruise control still works as does regen braking so I suspect speed sensors are fine.

C1202 says brake reservoir malfunction. But the fluid is and remains at the high / correct level.

Took it to Lexus, that day the fault was NOT on (typical) but still wanted them to check it out. They followed the procedure and said they looked over the system, cables etc and said no issue found, advised me to take out my Nextbase dash cam (new one which can only be powered via the OBD port). I am not convinced that is related.

The issue has been on and off since. I suspect it's moisture / water related but then yesterday was a hot day and it was on most of the day so even that doesn't check out completely.

I checked the voltages on the pins, cleaned them out with contract spray and high pressure air to dry them. Voltage / resistance stuff was as expected.

I'm at a total loss on what to do, or how to further troubleshoot. Though I am not overly familiar with circuit diagrams or electric troubleshooting I do most of my own work (servicing and part repairs when needed) to my cars except bodywork and tyres. So I'd like to give it a try, but my knowledge of hybrid specific stuff is not deep.

I have had a good search of the forums on here with people troubleshooting C1202 but many of the threads they either have a worse issue such as more brake booster codes and then the threads just stop with not always a solution.

Can anyone help? Very, VERY grateful for your help. If the forum supports donations and I somehow get this fixed for like say a month straight, would make a big donation!!!

 

Thanks for your reply @bisco. I have not tried that for long but Lexus did say that it could be interfering although I’ve had that since last July and the issues didn’t begin until February.

I held my iPhone under the reservoir yesterday and watched from my Apple Watch live as I pointed it around places I couldn’t see.

I found something bloody amazing in terms of a breakthrough. The bottom of my reservoir has exposed metal wires which show surface corrosion. They are missing the black plastic protection altogether. I have no idea how this finish could fail other than being exposed to fire level heat or being scraped off by hand. See my photos.

I found on eBay that nearly every example of this part from way older CTs have the black protective layer in tact. This is surely why mine works - thick metal in tact capable of passing a signal when dry and then when wet or humid, causing the fault light and C1202.

this is a new one for future owners of all these 3rd gen systems to check?

I have emailed Lexus as I have that ‘relax warranty’. Perhaps if they agree this is a material failure they can repair it without cost to me other than their second inspection of the issue which should be easy as I have shown them these photos.

if not… I believe from reading on here Toyota and Lexus dealers would NOT replace just this part if we asked them to and that they’d force the entire brake booster system. If that’s the case, I wonder why Toyota who replaced it last year did not replace this as well? Or… when they worked with the system why did they not notice this? If Lexus do not sort it, in fact, even if they do, I may approach the Toyota dealer and ask for an investigation. They weren’t interested when 50 weeks later this issue occurred as they said it was no longer warranted by them since my used car warranty had expired and that’s what their job was covered by in Feb 25.

Do you know if that is a Toyota policy that this must be replaced as a full system or just a dealer choice to do so, as when they inevitably try to tell me it wasn’t needed at the time, I would like recourse to Toyota and the warranty company who were likely paying out for this piece for it to not end up in my car. Etc.

 

Spoke to Lexus today. They reckon the protective coating on my reservoir cable is fine. Upon further inspection today.. I agree.

I joint the pins on the car end of the connection to the reservoir tank with a paper clip to simulate a ‘good connection’ since it’s a simple float switch and when connected, should give in theory solve my fault lights. Nope - no difference. Suggests the reservoir tank itself maybe fine.

my next course of action tomorrow is to check both ends of the PINK wire from the reservoir tank (car side of the cable) and the other end of it. It leads to the ‘skid control ECU’, pin 36 on my UK RHD car. To see if there is resistance or an ‘open’ in the circuit. I hope I’m using the right terms here.

if so, I can bypass it for a while and see if the system can go a few weeks without issue. Then… I’ll dig into the actual loom and fix the wire properly and reseal it all up.

If not.. Lexus can decide whether to replace the skid control ECU or the reservoir as these are both covered under the ‘Relax’ warranty. They told me wire loom repairs will NOT be covered unless they are connected to the part itself (e.g. how the reservoir has its wire seemingly glued into its bottom. But not the loom it plugs into).

this is all going by the diagrams I found on the leaked Tech Doc system from the CT forum. I presume you guys have something similar for the Prius. If not worth grabbing a copy as I think it’s basically a 3rd gen system and identical