Fault codes 28 and 29

[mattmanic]

Hello,

 

My '98 GS300 randomly goes into limp mode, a couple of times a month, I checked the codes by bridging pins E1 and Tc under the bonnet and got 28 and 29. I believe those are the main and sub o2 sensors. It seems strange that they'd both go, could it be someone else causing the codes?

Of course, I don't know for sure that its this causing the limp mode...

 

Thanks :)

[ColinBarber]

If the main sensor plays up you are likely to get errors on the downstream (sub) sensor as well as the mixture will be incorrect which fools the sensor into thinking the cat isn't working correctly. A faulty sub sensor cannot cause a fault on the main sensor. Therefore concentration on the main sensor first, you are correct to assume two sensors wouldn't go faulty at the same time.