My check engine light comes on . it read that my oxygen senseor or is it my cat-convertor?.is it regular problem with these chevy cargo van 2004 express

Well you would need to use a scanner to monitor the data coming from the sensor after the cat. Code 137 means the data voltage is too low or zero. The sensor generates ac voltage based on the amount of unburned oxygen in the exhaust.
The actual problem could be an exhaust leak closer to the engine, or that new cat may not be up to oem standards.

what kind of codes you have?.try to reset,how many came back.

0174 is system too lean, right bank. 0420 is catalyst sytem efficiency below threshold, left bank. fix would be either oxygen sensor or catalytic converter replacement possibly would need both. note: this veh would possibly have up to 4 oxygen sensors, but cause of problem would be the ones coming off manifolds before the catalytic converter possibly in manifold or y-pipe/down pipe.

Oxygen sensors are located in your exhaust usually 2 - 1 upstream (in front of cat.converter) 1 downstream (behind cat.converter) and from under the vehicle.

p0420 is Catalyst System Efficiency Below Threshold (Bank 1) o2 sensors reading are used to check the cat if the cat is plugged you will lose power o2 sensor send a voltage signal to the computer 0 to 1 volts The o2 upstream of the cat should switch back and forth from 0 to 1 volts, average .450v if voltage stays high engine is running rich (low oxygen) if voltage stays low engine is lean (lots of oxygen) cats have a 8-year 80000-mile warranty

most any sensor going bad can cause the check engine light to come on,try disconnecting the posative battery cable for 15 seconds ,then put it back on,will reset the codes, or take it to auto zone,they will test your computer for codes at no charge to you.i had a venture van my was ox. sensor. thanks robert b.

I would try to clean out the egr valve , check for leaks at the evap canister, check the evap canister soleniod , and lastly change out the cat convertor, The cat convertor is most likely under the federal emmission warranty of 8 yrs,.80000 miles. You can take the vehicle in to have checked by local dealer or call gm customer service to check the warranty on the cat. convertor by giving them your vehicle number.

You have a V6 engine, bank one is the row of cylinders on the passenger (right) side, bank two is the row of cylinders on the drivers side (left). Your codes indicate an inefficiency in the cat on the left side but this could be due to a bad O2 sensor or an engine that is out of tune and overloading the cat. This car seems too new to have a bad cat. I would change the plugs and the O2 sensor after the cat before going any further. The reason I say the O2 after the cat, it's the one that is critical in sensing cat efficiency. What is the mileage?

I think you will find the aftermarket Cat Conv. is the source of your problem, but without hooking up to the factory test equipment at my disposal at my Ford dealer this at best and educated guess based on 20 years of emission related work, I am a Ford certified master electronics technician

there are 3 one on each side of eng. on the Y pipe one behind the cat. convertor. not to hard change