yodapwnedjoo

my cel came on today with a code 27

--SUB-OXYGEN SENSOR CIRCUIT OR SUB-OXYGEN SENSOR HEATER CIRCUIT

--SUB OXYGEN SENSOR/HEATER/CIRCUIT

--ECU

Both the oxy sensors are plugged in.

The truck seems to run ok .
OTHER than the fact that I have an exhaust leak at the exhaust manifold . (manifold is warped ) , trying to find a replacement currently.

Would the exhaust leak at the manifold cause a code 27 ?
Also my catalytic converter is hollowed out on the inside i noticed.
but its been that way ever since i bought the truck yrs ago .
never threw a code until today.. so im not sure if that has anything to do with it.

Other than that I did just have to replace my head gasket a few weeks ago , so maybe any water in exhaust could have messed with it ?
any way to test the sensor or wiring to it ?

Thanks for any help .

scope103

It's not the exhaust leak. The sub O2 sensor monitors the catalytic converter (if both o2 sensors swing together, the cat is bad). Why you haven't had this code "ever since" I cannot explain.

It is possible you've just taken out the heater, which you check the same way as you do for the upstream O2 sensor (you've been on this site for more than 3 years, so I'll assume you know how to do that, or where to look). More likely, it's just now noticing that your cat is bad. The test procedure for the sensor part, not surprisingly, assumes you're not supposed to get a code 27. If after checking the wiring you still get code 27, it recommends you replace the O2 sensor. Which in your case ought to be a waste of time, because based on what you say you ARE supposed to get code 27.

bswarm

I have seen O2s go bad after a head gasket failure. Or using RTV sealant in the wrong place that finds its way to the O2.