2007
22k miles
intake
header
HFC
exhaust
Hondata Flash

so i threw a P0135 primary O2 sensor CEL. cleared the code with my scan tool and 5 seconds later later the CEL comes back on with a COLD engine.

if the CEL was going to come back on shouldn't it have came on after the car warmed up a few miles down the road. thought the car would be in closed loop mode and not relying on the primary O2 sensor during warm up.

i went under the car and the harness does not appear lose. car seems to run perfectly fine at idle, partial, full throttle.

so based on the above could it still be a bad sensor or another problem?

thanks all.

 

You need a new Primary 02 sensor.

 

Ok, before you spend the $100 or so, here's a diagnostic DIY-check for the heater circuit (which is the code):

Get a 20 Ohm 10Watt ceramic resistor (or 2 connected in series, Radio Shack # 271-0132).

Now take a look at the 4 wires coming from the oxygen sensor: 1 gray, 2 white, and 1 (black? red?). The 2 white ones are going to the heater coil, so cut the 2 white wires, and hook up the resistor between them (or 2 in series). They (it) _has_ to be 20 Ohm, 10 Watts. After clearing the CEL, start the car. Watch the CEL not come up. If so, the simulated heater element fooled the ECU into thinking the heater element works ok. Now you know for sure the heater element is dead.

One thing, you might get a CEL, something to do with expected time to warm up, or coolant temp not up to temp. That's also confirmation for a bad heading element. Replace the O2 sensor.