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Discussion Starter · #1 ·
Hei everyone, I hope you are doing great.

I bought my 2008 IS350 about a year ago and it has been awesome, aside from the Check VSC message on the instrument cluster. Allow me to further explain:

The "Check VSC" message surprisingly showed up for the first time immediately after filling up the gas tank with 95octane gas [the previous owner never mentioned nothing about this]. Aside from the Check VSC message on the instrument cluster there were no difference on my driving experience, everything felt normal, after like a month when I was driving my way to work and the car went to "Limp mode" [rpms wont go higher than 2000]. Since then I have tried several things, and the code always comeback. This is the order of the things I have tried after mainly exploring the web looking for solutions and considering other people experiences:

-Disconnected the battery = clears the code, but it randomly shows up again. As you may know, this actually clears everything, so this is no solution.
-Cleaned the MAF sensor with CRC Electric Cleaner
-Cleaned the Throttle Body with CRC Throttle Body and & Air-Intake Cleaner
-Replaced all 4 wheels Brake Pads with OEM ones
-Cleaned all 4 brake rotors and calipers with CRC Brakleen
-Replaced the fuel tank cap [I always fill up the tank up to its max point, no further, and close the cap after just one click, at the gas station]

The Check VSC message kept coming back, and as a consequence I continued getting into Limp mode randomly, so I decided to get myself the Bluetooth OBDII scanner. Scanning my car after getting into Limp mode I got C1201 together with P0504, P0175, P0172 and P1170, and I did the following:

-Replaced 6 spark plugs with OEM ones
-Disconnected and cleaned with CRC Electronic cleaner the 4 connectors that go into the Injector Driver ECU. Also cleaned/brushed the ground connections of this DCU.
-Replaced the PCV Valve
-Replaced the Fuel Filter Assy OEM
-Poured a 473ml bottle of Cataclean into may fuel tank when there was 1/4tank remaining [as per Cataclean indications]

So after the above the Check VSC kept coming back, and every now and then I have been going into Limp mode [I can get out of Limp mode by turning OFF the engine and starting the car back, but this is so annoying while daily driving as you might imagine].

Trying to go a little bit further I followed the advice of doing the "Zero Point Calibration" through Techstream [I got it from ebay] by selecting the ABS/VSC/TRAC "Utility", and executing the "Reset Memory", and then a "Test Mode". After these I cleared all DTCs, and after a day without any issues today I got the Check VSC message again. Doing a Health Check on all DCU I am getting C1201 together with P0175, P1170 and P0504 [I attach to this post the Freeze Frame Data Report from Techstream for each one of these].

The TIS Repair Manual suggests to replace the ECM, and if that does not do it then to replace the Skid Control DCU, but I have a hunch that this might not solve the issue after everything I have done. And seeing C1201 constantly together with the other codes I am starting to believe that it might just be a "consequence" DTC and not the root cause of whatever issue my car is having. Honestly, I have no expertise in Toyota/Lexus cars, and I cannot see how P0175 [System too rich], P1170 [Fuel Performance/Fuel Injector], or P0504 [Brake Switch A/B correlation] might be related to C1201 Check VSC and cause me to go to Limp Mode [unless this is some kind of engineered behavior to protect me as a driver from an accident by going to fast on the road], and all this time I have been troubleshooting the wrong code or starting from wrong assumptions about the root cause.

I would highly appreciate any feedback or tip to continue troubleshooting this issue, if anyone could take a look into the data attached to this post and provide some lights to what to look at, which parameter is out of range, what part could be affected, I would highly appreciate it.

Thanks!
 

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With most of the codes being related. If you cleaned the Maf and it is in proper voltage range. I would think it may be a falt in the the injector or harness to an injector. You do have one code for your brake light switch also.
 

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Discussion Starter · #3 ·
With most of the codes being related. If you cleaned the Maf and it is in proper voltage range. I would think it may be a falt in the the injector or harness to an injector. You do have one code for your brake light switch also.
Hei, thanks for your feedback!

I forgot to mention about this, but I checked on my rear brake light, and both lamps, and all of the 3 turn on when I push the brake pedal...I also check on my brake fluid level and it is at max level.

Please let me know your thoughts, thanks!
 

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Hei, thanks for your feedback!

I forgot to mention about this, but I checked on my rear brake light, and both lamps, and all of the 3 turn on when I push the brake pedal...I also check on my brake fluid level and it is at max level.

Please let me know your thoughts, thanks!
It is a signal issue with the switch on the pedal to the ECU. Just replace it.
 

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Discussion Starter · #7 · (Edited)
Did you check the voltage range on the MAF?
Hey Solar.

I will take a look into the Air Fuel ration Sensor and would share the results. Before that I will take a look into the brake pedal sensor and circuit, as the repair manual indicates that "If any DTCs other than P0171, P0172, P0174, P0175, P1170, P117B are output, troubleshoot those DTCs first.", so I will start with P0504.

Thanks !
 

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Discussion Starter · #8 · (Edited)
It is a signal issue with the switch on the pedal to the ECU. Just replace it.
Hei Solar,

So today I did a couple of checks, with the car parked:
-Visually confirm that the brake light and both brake lamps when I pressed the brake pedal = all 3 lamps turned ON "normally", I noticed they went ON and OFF as I pressed/depressed the pedal without any delays or lag.
-Monitor the "Stop Light Switch" in Techstream = The status of this signal changed between ON and OFF normally as I pressed/depressed the brake pedal, no lags/delays noticed.
-Checked Fuse #18 = normal condition with continuity measurement with multimeter.

What I haven't been able to check:
-Voltage measurements as indicated in the TIS repair manual between ST1 and E1 pins = I was not able to confirm the location of E4 and A5 in the ECM, the connector layouts in the manual does not match to the ones seen on my ECM, dont know why...
-Inspect the Stop Light Switch Assy = cannot remove the switch, it is hard to rotate it either clockwise of counter clockwise. I sprayed it with some WD-40 and will come back to it after a couple of hours...would you have any tips on how to take it out? is it clockwise?

So far on what I have done, would you consider the Stop Light Switch Assy, or circuit, to be compromised?

Thanks again for your support!
Automotive tire Motor vehicle Gas Electrical wiring Auto part
 

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If Techstream confirmed. Then the only thing would be resistance change. Try replacing bulbs or cleaning the bulb connections. Voltage measurement is usually done at the MAF connection point.
 

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Discussion Starter · #10 · (Edited)
If Techstream confirmed. Then the only thing would be resistance change. Try replacing bulbs or cleaning the bulb connections. Voltage measurement is usually done at the MAF connection point.
Hey Solar, how are you? I was able to take out and inspect the Stop Light Switch Assy:

1. Resistance between pins 1 and 2 is below 1ohm for pedal not pressed, and goes above Mohms when pushed = normal
2. Resistance between pins 3 and 4 is above Mohms for pedal not pressed, and does not go below 1ohm when pushed. Actually it does not go any lower than kohms range = abnormal, according to Repair Manual it should go below 1ohm.
3. With a Test Light connected to the chassis its bulb turns on when put in contact with pin 1, and also for pin 3 of the harness that goes connected to the Stop Light Switch Assy = I think this would discard any blown fuse or harness issue.
4. From Techstream Data List I monitored the Stop Light Switch and Brake Pedal Load Sensing Switch = both turned ON and OFF as I pressed/released the brake pedal...sometimes I noticed that there was a delay between both signals status update, but most of the time they changed simultaneously...don't know if the delay could be a sensor status refresh rate from Techstream, or if there is an actual a delay on the switching status update from the Stop Light Switch Assy itself..
5. I had cleared all DTCs yesterday and have not driven the car since 2 days ago. I ran a Health Check not too long ago and P0504 was detected, so it must have appeared while I was troubleshooting the Stop Light Switch Assy today and yesterday...but there was no Check VSC on the instrument cluster, or C1201...

I cannot conclude 100% if the Stop Light Switch Assy is compromised based on the above, but I am considering getting a new one because of #2 test above result.

Anyway, during this week I will continue monitoring the DTCs every time I drive the car to see if P0504 comes up, and when it does, if the Check VSC or C1201 show up as well.

Please let me know your thoughts.

Thanks!
 

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Discussion Starter · #12 ·
I would replace the brake switch. Even if it comes back. It seems the most likely and cheap to try. I am also still thinking the MAF is bad as well.
Hey Solar, wanted to share an update:

So the P0504 has shown up today, but no Check VSC no Limp mode no C1201...and this time on Techstream the Stop Light Switch signal remained OFF even when the brake pedal was pressed and the light on, so I will replace it...

While I wait for the Stop Light SW Assy I will continue monitoring my car codes and will share any updates...next I will take a look into my Long Term Fuel Trim, I think it is high for both banks so will figure out how to test the MAF with multimeter and Techstream, hopefully it is not something more serious like the catalytic converter? I attach to this post my last Health Check from Techstream. Any comments on this please let me know.

Thanks!
 

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