98 Civic LX with Code P0135 and missing engine.

[TarHeelBlue]

I have a 98 Civic LX that's completely stock I bought last year to use at my part time job delivering pizza.
The car has been dependable and easy to maintain until lately.

I noticed the car missing a bit when I was stopped at a light and it struggled to accelerate. Shortly after this started the CEL came on throwing code P0135. When I pulled the sensor to replace it I noticed the manifold was cracked. Replaced the manifold and cat, put in new 02 sensors and still getting the same code and symptoms. Tested the harness with a multimeter and I'm getting no ground for the O2 sensor heater circuit. Probed the wire behind the connector and nothing. According to the manual the ground is provided by the PCM itself so I replaced it with a good PCM and got the same code and symptoms.

I tried splicing the heater ground wire on another sensor I had and ran it directly to the thermostat housing ground, expecting the sensor to work properly but the check engine light to remain on due to the computer not registering a ground. No results.

At this point I am at my wits end. I have replaced the manifold, cat, 02 sensors and PCM with no change. The only thing I can think to do next is replace the wiring harness from the PCM to the engine and sensors, I am thinking there must be a broken or shorted wire somewhere along the path. I replaced the sensors with Denso sensors that are a fit for this vehicle.

Anyone have any suggestions on this? I have read that fuse #15 under the dash can burn out due to a wiring harness contacting the intake manifold bracket on the bottom of the car and intend to check this out today but I would assume this would provide the power and not the ground.

All of this comes on the heels of our 07 LX going into the shop for an engine replacement after the block cracked. Luckily that one was covered under warranty.

 

[lethal6]

We had a tech here at work with the exact same problem. He tested pretty much the same way you did, with also swapping out a known good ECU and the choose just kept coming back. Turned out to be the aftermarket parts thrown in the car to save money. These Hondas don't like aftermarket sensors. Did you get the sensors from Honda?

I had a pesky code in mine for O2 sensor that kept coming back even with new sensors. It was the aftermarket ones I put in to save some bucks that f**ked me in the end. Put some expensive ones in from Honda and it ran like a champ until she was totaled by an idiot on a cell phone.

Not saying that is your direct issue, but I have seen it more than once.

 

[TarHeelBlue]

Thanks for the response. I didn't go to the dealership and pick the sensor up but I did get a Denso which is as close to oem as they had.

Just a little more info, the miss and slow acceleration only seem to occur when the car reaches operating temperature although the cel is steady. I'm not sure if this is due to the fact that the car is running a preset A/F mix before trying to get into closed loop mode via the 02 sensor. I never got a chance to look at the wiring around the intake manifold bracket but I'm going to do that and try to back probe the ground as far as I can follow it in the harness.

I'll definitely get in touch with the dealership and see what they have as far as original 02 sensors go, if that doesn't solve the problem I plan to get a harness from the local Honda yard and install it.

 

[TarHeelBlue]

I got a chance to put the car in the air and take the intake manifold bracket off. The plastic tubing was already in place over the wires and I didn't see any damage. Fuse #15 under the dash was good but I still swapped it out to be sure. Got a new 02 sensor from the dealership for just over 140.00 and still no change.

I'm starting to think the issue could be somewhere else and just triggering the 02 sensor code as unplugging the 02 sensor completely has no effect on the miss or idle. I checked the TPS today and it's good. I want to change out the PCV valve and either replace or clean the IACV next. The rpm's seem to jump around alot but once it gets past 2500 everything smooths out.

 

[TarHeelBlue]

Just wanted to post an update that the Civic is now running normally again. I ended up replacing the harness which was corroded and splitting where it goes through the firewall and that brought the 02 sensors back online. New plugs, cap, rotor and wires took care of the miss. I had a few days off due to the snow so I went ahead and replaced the PCV Valve. Took the throttle body off and cleaned it real well along with the IACV and put a new gasket in. Replaced the valve cover gasket, plug tube seals and grommets. Been about a week now and still no issues and the car passed inspection.