Looking for a lil help for a poor college student.
2004 Honda Civic EX with 100,000 miles
I noticed the heater has not been working. Coolant level is fine, and checked the fuse for the heater and it's good..it just blows cold air. Also, I noticed a check engine light. It was read, here are the results:

Check engine light: p0135
Def: A/F sensor 1 heater system malfunction (probable cause)
aa1 open or short circuit condition
aa2 Poor electrical connection
aa3 Faulty A/F sensor 1

Any ideas? Not sure how a 02 sensor can cause these (heater blowing cold air)symptoms if that's what the CEL is saying...
Any input is appreciated as I did a search and it seems it's prob the 02 sensor closes to the motor...
Thanks,
Joe

 

This is probably two problems.

Does the temperature gauge go up to normal? Also you could open the hood and carefully touch the coolant hoses to see if they're hot. If the thermostat is stuck open, the engine will stay cold and the heater will not work much if at all.

On the O2 sensor, unplug it when cold and measure the resistance of its heater circuit (the two wires that are the same color, usually black or white). If it's open circuit, replace sensor.

 

Thanks for the input...
Yes the temperature gauge does go to normal, however, I did not mention earlier about a month ago, the temperature gauge went to H and I put the heat on to cool the motor and the heat worked...it has not done this since.
I just took the car for a drive and noticed that the top hose coming off the top of the radiator was warm while the bottom hose was cool to touch....Is it safe to say that a bad thermostat can cause the heater not to work?

Regarding the 02 sensor, I'm guessing you are referring to the 02 sensor at the front base of the motor by the exhaust manifold?

Thanks for the input,
Joe

 

Have you checked the coolant level in the radiator itself? Don't just check the plastic tank. Remove the radiator cap (engine must be cold) and the radiator should be full to the top.

Yes a P0135 relates to the first O2 sensor, the one closest to the engine.

 

I just checked the coolant level in the radiator itself. And no coolant spilled out and no overflow...seemed dry, so I'm guessing I'll pick up a lil distilled water later and top her off at the point of entry at the radiator cap. Sound like a good idea? or any more input is greatly appreciated...
Thanks for your time

 

Like I said, it should be full to the top. If you can see the top of the core is dry, it's really low. I suggest putting in premixed coolant so you don't weaken the antifreeze by just adding water.

 

Wow, well done...I was able to put about 1/4 of gallon into the top of the core, and guess what? The HEAT works!
Thanks a bunch for your expertise.

Now I must tackle the p0135. I would imagine 9/10 of 10 especially for a car with 100K it's the 02 and not the harness....