The code is po138 what is it

https://www.obd-codes.com/p0138 https://www.autocodes.com/p0138_chevrolet.html

P0138 - Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 2)

Fault codes never say to replace parts. They only indicate the circuit or system that needs further diagnosis. The only way to set this code is to have a break in the sensor's ground wire or the signal voltage wire is shorted to the 12 volt heater wire for that sensor. Start by looking for a corroded terminal in the sensor's connector or a terminal that got stretched or pushed out of the plug body. Next, check the wiring harness for signs of melted wires, especially where they travel near hot exhaust parts.

If you haven't found the cause by this time, use a scanner to view live data and look at the sensor's voltage compared to the passenger side sensor. If it's normal, you have an intermittent problem that isn't currently acting up. Try flexing on the wire harness to see if the voltage changes. If the voltage IS high, unplug connectors going to that sensor and wiggle harnesses until the voltage changes. That will help you narrow down the location of the problem.

P0037 is "Heater Control Circuit Low Bank 1 Sensor 2".
P0138 is "Oxygen Sensor High Voltage".

It sounds like it's time to check the connector to your oxygen sensor, and probably replace it (the O2 sensor).

Code 138 is O2 sensor 1/2 circuit high voltage. This means the sensor after the catalytic converter on the side with cylinder one is staying in the rich range. The sensor could have failed or it could be a fuel problem in the engine.

air fuel ratio sensor ,the back one is not reading correctly.have a scan check & read the sensor.most likely is the sensor .bank one ,the back (rear)one

do you have two o2 sensors after catalytic con.could be not good.

yes replace the oxygen sensor

p0203 injecter circuit malfunction cyl #3. p0204 injector circuit malfunction cyl#4. po138 02 sensor circuit,high voltage cylinder bank no.1,sensor no.2

code p 0138 refers to 2 items
1--heated oxygen sensor(HO2S) 2 bank 1--high voltage ==causes --wiring short to positive --HO2S---ECM
2--oxygen sensor (O2S) 2 bank 1--high voltage ===causes wiring short to positive ---ECM
code p 0139 refers to 2 items
1--- heated oxygen sensor (HO2S) 2 bank 1--slow response ===causes --heating inoperative --wiring--ECM
2--oxygen sensor (o2S) 2 bank 1 slow response ===causes --wiring --- O2S

heated oxygen sensors9HO2S) are in the exhaust manifold before the cat converter
Oxygen sensors (O2S) are after the cat converter
it is indicated that the HO2S is faulty-
check the wiring and /or replace both sensors

did it fail high hc? you could change 4and 6 coils around and see if you get a p0306 that means the coil pack is bad. common on this type.