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Check Engine + VSC and associated issues

6K views 3 replies 4 participants last post by  knightslugger 
#1 ·
My check engine & VSC lights came up one fine morning. The obd scanner showed only the gas cap open code but not the VSC. I checked and sure enough, the gas cap was not fully closed.

The VSC was defeated and not working (I checked by doing some hard accelerations on slippery surfaces and that "chatter" was not there, letting the wheels spin crazy) but the scanner didn't show anything for it. My search revealed for the VSC light the yaw sensor might be off calibration and a dealer should be able to fix that. Anyways.

I closed the gas cap properly and didn't reset the check engine light from the scanner. I wanted to see how many miles would it take to reset that light on its own. It turned out that after around 225 miles of closing the gas cap properly, when I parked the car overnight, the next morning both the check engine & VSC lights were gone. I was surprised to see the VSC gone too.

I immediately did a few hard accelerations on slippery surfaces and sure enough the VSC was working. From this I gather, that the check engine light made the VSC come on and when it went off, so did the VSC. I will do this whole exercise again by leaving the gas cap open to establish:

1. How many miles does it take for the open gas cap to trigger the check engine light
2. Does it take around 225 miles to reset that light on its own
3. Does the VSC light come on with the check engine light and defeat the VSC

This all episode happened when I was almost at 30k miles and during these lights coming and going, the Maintenance Required light didn't come!

I was wondering if anyone else has experienced this.

Thanks
 
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#2 ·
Your not alone, many have asked the same question. Not clear why the CEL and VSC are attached, but the CEL/VSC coming on together is "normal" for some codes.

To answer your other question, its less about the gas cap CEL, and more about the ECU monitoring the engine. Its normally a few engine cycles to verify a CEL has been remedied, then the light goes out. The cycles are a combination of the car sitting, starting, warming up, being driven for a period, cooling down. Depending on that cycle the miles could be more or less.

You were smart to let the CEL go out on its own, the only real way to know its fixed. Maintenance required/service engine soon lights are different than a CEL. Perhaps thats the answer there.
 
#3 ·
Toyota considers VSC to be a secondary system. If something is wrong with the engine (from gas cap to misfire) the VSC and TRAC systems both shut down. When checking the corresponding VSC or TRAC ECU the code is always "Engine Control Malfunction".

Clearing the ECU by erasing the code will get it working sooner. Toyota uses the 32 key cycles logic for code clearing. Meaning if the problem does not reoccur for 32 key cycles it clears the code.

So in summary if your Camry, Highlander, etc has VSC and TRAC and your check engine light illuminates you will always have a VSC and TRAC light on. If just the VSC and TRAC are on something is wrong with those systems (zero point, ECU, etc.)
 
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