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Skyvisions, ASE Certified Technician
Category: Lexus
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Experience:  Lexus Expert
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The check engine and Trac lite on at same time..OBD

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The "check engine" and "Trac" lite on at same time, reset and 1000 miles later same thing. Checking OBD gave codes p0446b and c1201. Thoughts on problem (s)?

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If you clear the codes does the p0446 come back consistent and do you ever get a 441 or 440 with it?



Customer: replied 5 years ago.
Yes the same code both times p0446 & c1201.

The P0446 code generally is related to a leaking evaporative emissions switching valves either the close canister valve at the air cleaner lid or the vapor pressure switching valve on the charcoal canister itself. I have seen both of these go bad. The most common of the two is the one on the charcoal canister. This is especially true if you live in the Northeast were rust and corrosion are an issue. Given the age most places or dealerships usually just replace entire charcoal canister because it comes with the vacuum switching valve and it's not much more. Usually the diaphragms in the charcoal canister will also leak and nine times out of 10 you will replace the vacuum switching valve only to get bit and have to replace the whole canister anyway down the road. Without doing proper pressure test and evaporative emissions testing is difficult to say for sure these are just the common issues. As far as your 1201 code this code sets by default whenever there is an engine control malfunction. This in turn causes the vehicle skid control light to illuminate.



Customer: replied 5 years ago.
I am a little confused. My manual says nothing about the Trac light being used as a general fault per your explaination of c1201 fault. I read c1201 as an Engine Communiations circuit. Are you saying when there is a c1201 fault the Trac lite comes on even when there is no problems in the Traction Control System.?

Essentially that is correct. Whenever there is a malfunction in the engine control computer the traction control computer does not know what this malfunction is or how it is involved in controlling the traction control system so it sets a communication error and shuts the traction control system down. You can't have the traction control system trying to operate and control the stability of the vehicle or traction if there is a major component failure electronically that supports the engine control system. Any time the check engine light comes on for whatever reason emissions related or sensor input related you always have the C1201 fault code set. This is done for safety reasons.



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