Ok so I have codes p1381 which is CYP intermittent interruption & p0135 which indicates primary heated o2 sensor heater circuit fail. Tested if there is voltage from the electrical connector that connects o2 sensor and there is a good voltage passing wanted to know if there was anything else to check before buying a whole new o2 sensor like what a burnt out o2 sensor would look like?

Now to the CYP sensor, tested electrical current between the electrical connector of the dizzy. Opened the dizzy cap and no oil neither corrosion & there was great voltage. I still get thrown these codes after disconnecting the back up fuse for 3 mins and driving it around... Says in my repair manual to replace dizzy but do I really need a brand new distributor over one sensor? It's killing my gas, I get roughly 230 miles a gallon city and that's horrible for a 99 civic DX all stock motor.

 

Let me correct myself 230 miles a tank.

 

Start with the O2 sensor. The car is probably running in limp mode right now since it sees a bad sensor.

 

What's limp mode? I've read that when it's a bad sensor the PCM stays in open loop mode

 

Exactly.

 

no, no. the CYP error dumps in fuel, which is causing your O2 failure. the most likely case for CYP failure is wiring. it's a pretty isolated circuit, just check the wiring from the dizzy to the ecu, look closely for exposed wires, loose plugs or pulled out pins, corroded pins. Then replace the distributor. then replace the ECU.
then replace the O2 because you fouled it out from running in limp mode for so long. yes, it's bad, I can guarantee it.

 

Good point on the CYP.