2005 Honda Civic EX O2 Sensor

I have a 2005 Honda Civic EX with the 1.7 engine (as they all have.) I recently started getting an ECM code of P0135, which indicates the heater element on the pre-converter O2 sensor is not working properly. Along with this code, I have gotten three codes for cylinder mis-fires: P0300, P0301, and P0303. The physical problem I see is when I sometimes start the car, especially when it is cold, the car runs rough for 1-5 seconds, then runs normally. I assume the heater element in the O2 sensor is faulty, and causing the sensor to send faulty data to the ECM, causing the car to run rough. Any other suggestions/alternative ideas before I drop $300 on a new O2 sensor?

I’d make sure that the connector is seated well. Not absolutely sure of Hondas but very often there’s have a clip over the connector that could have popped off, causing it not to make proper contact.
It is likely heated so you should be able to measure the resistance on the heater coil. It usually is around a couple of ohms* or so. If you don’t see that, the thing is definitely bad.
Once you identify which wires are the coil, see if you measure 12V on the connector. You should be able to unplug the sensor and just turn the key on to the pre-start position.

*Check your tech manual. It being a coil, it often has very little resistance but more than a short would be.

The O2 sensors are not relevant to cold starts as the PCM doesn’t use any info from them until the car is warmed up, so I would ignore the O2 sensor for now and look at other things.

How old are the plugs & wires? Filters? Check your coolant temp sensor.

Cig, isn’t that 0135 code usually related to the ECM not measuring current going though the a/f heater coil?
No doubt you’re right it isn’t really used when the car is cold, though.

$300 for a heated oxygen sensor?? Most of them can be found for under $100…

Thanks, didn’t think about the O2 sensor not being involved at startup. I had the codes re-read at a different shop, and I’ve also got several codes regarding the EVAP system: P0497, P1456, and P1457.

As for plugs and wires, the plugs were replaced this summer with OEM plugs. No plug wires on this car; each cylinder has its own individual coil that mounts directly onto the plugs.

As for coolant temp sensor, not sure how that would affect the car at startup?

RemcoW - as far as I know 0135 isn’t about finding current. Its just about timing - how long it takes the O2 sensor to start switching. The heated circuit in there decreases the time to get to closed loop. So AFIAK its just about how long that takes to get there.

For GungaD, the coolant temp sensor (and coolant temp itself) is crucial to the fuel mix. If it reads off the PCM thinks the engine is colder/warmer than it really it is. This will create a fuel mix that is too rich/lean. So one possibility is that the coolant temp sensor is off, giving the PCM info about the car being colder than it really is. It creates a too-rich mixture & you get misfires. Or vice versa on the temp reading thus going too lean.

The thing is that if the temp reading isn’t out of possible spec the PCM won’t know its wrong - so you wouldn’t get any codes that might lead you to it.

If you have a multimeter checking it is really easy. You can probably get the resistance specs from Autozone’s online repair info - then you just measure according to actual temperature.

Gotcha. I didn’t know that about the A/F sensor - goes to show one learns something new every day.

Well, I didn’t write any books about it & I’m just a shade tree guy - so I might not have it all together in terms of the interpretation. Either way, the first thing to check is actually the circuit/wiring itself. In this case I just figure this car obviously has other problems & O2 codes are so fickle I usually figure on ignoring them until any other issue is solved first.

It’s all coming together now. A month ago I had to bleed some air out of the coolant system. (I suspect there is a small leak in the radiator, as I can sometimes smell antifreeze from the front of the car, but the shop didn’t find anything with a pressure test.) Despite the coolant I used saying it is compatable with Japanese cars, I wonder if using that coolant may be causing the problem, or if running the car with too little coolant may have damaged the sensor. Now I just have to find my multimeter so I can start checking the sensors.

Have you been losing any coolant? Do you know how/why the air got there or are you assuming it’s the potential radiator leak? I hate to say it, but if I see misfire codes plus bubbles in a cooling system…I’m thinking rule out a head leak now.

Not wanting to discourage you but do know that using regular antifreeze sold at the FLAPS is referred to as “HondaCide”…
They are picky when it comes to coolant.

Not discouraging at all. If anything it tells me I should make a plan to visit a Honda dealer. I do not know how the air got into the system. The pressure test did not find any coolant leaks or pressure changes in the system. As said before, I can sometimes smell antifreeze from the front of the car. But I have yet to see physical signs of a leak. Have I ruled out a head gasket leak? There is no visible sign of antifreeze in the engine oil, or of hydrocarbons in the antifreeze, and the pressure test did not point to a head gasket leak. But that doesn’t mean the head gasket leak doesn’t exist, and it’s still on my list of culprits.

The way I understand it, Hondas/Acuras require silicate free coolant.
Most sold at the regular parts stores are not.

It apparently does a job on the gaskets and waterpump so I’ve always used the dealer coolant.

I went out to start the car this AM to take it in for a diagnostic. And the head gasket finally gave out. Apparently it was a very slow leak and today is the day it finally gave way. Gold star to Cig for calling it.

Sorry to hear that. Edit: not that ciggie was right - that your car blew a gasket, that is.

Thankfully I was only going across town to the Honda dealer, and not on the road to downstate Illinois from Chicago. Funny though, when talking to the dealer mechanic, I said, “if this were a six-year old American car you might talk about junking it with a blown head gasket. Since it’s a Honda it’s still got 150K miles left in it, so you fix it.” He nodded and said, “That’s why I left a Chevy dealer for Honda. And it looks like you’ve been taking care of it, so I am gonna agree with you.”