VSC/TRC Lamp Lit

[IanML]

Just noticed the VSC/TRC lamp is lit.

Toyota Techstream gives no fault codes except one for catalytic converter efficiency low, despite the fact that I only had the body ECU selected - is this credible?

Any advice gratefully received.

[gjnorthall]

You don't mention if the check engine light is also illuminated? If so, it's a quirk on many Toyotas that certain faults, such as faulty Lambdas will trigger the VSC light. There is obviously no relationship - it's just that the check engine signal affects the VSC processor. If the only fault indicated is low catalyst efficiency then a brisk drive will often allow the engine light to be extinguished and stay extinguished. It can also occur if the bottom sensor gets soaked driving in heavy rain.

[IanML]

Yes, the CEL is also illuminated, due to the cat converter efficiency code, but a link between that and the VSC indication would never have occurred to me. 

I live in Jersey, so the car does a lot of puttering about and short runs, which may explain the cause. Than you very much for your reply - a brisk drive shall be performed tomorrow (can't exceed 40 here, but I'll keep the transmission in 2 to keep the revs up), and I'll report back 

[gjnorthall]

If the fault keeps reappearing then it’s either a cat converter issue or a lambda issue. On a well maintained car - a cat issue is rare but the response from a sensor deteriorates with age. The ECU does a comparison routine on the sensors and initially records a preliminary code. If the fault repeats then a fault code is flagged. It might therefore take some time for a low efficiency code to reappear. It’s often wrongly concluded that the sensors are doing their stuff and it’s a cat fault. A life expired sensor won’t throw up a code which again leads to wrong conclusions.

[IanML]

Thanks for that - is there any strategy for identifying a life-expired lambda sensor, or is it suck-it-and-see (££££££)?

However, hopefully I won't need to.  I did the "Italian tune-up" this morning, and then realised why I had not been able to clear the DTC yesterday - I had not highlighted it before clicking "clear" ..  Having cleared it, did what passes for a long run on the island, and it has not returned.  Fingers crossed. 

[gjnorthall]

The output of a lambda cycles between about 0.1V and 0.9V around once per second. It's basically a case of looking at the output trace on an oscilloscope or a hand held digital display.  A life expired Lambda will cycle significantly less than once / second or the output trace will be quite flat. Often the Lambdas on this engine suffer from heater failure well before the sensor element is life expired.

[IanML]

Thanks.  Well, I assume that heater failure is signalled by a fault code, so the chances are my lambdas are ok,  and I'm hoping the cat efficiency code was cured by the Italian tune-up.