98 civic dx hatchback, 100k miles, all stock, wife's car. check eng light came on yesterday and car began to idle low and stall intermittenly at stops. local independent honda shop coded PO135, (indicates a failure in the oxygen sensor heater circuit bank 1 sensor1). their recommendation/esimate to replace the primary sensor $320 more/less. also recommends replacing aux sensor because its failure tends to follow primary's, (another $320). these guys have done all service on the car and have the trust of my wife but $700 with no guarantee that the car won't continue to stall.

should i explore other potential causes? what are other causes for the low idle/stalling? try to change sensors myself? i'm no mechanic but consider myself capable in the garage.

i will say that the idle/stalling and check eng light probably are not a coincidence. thanks for all help. dan

 

That code says that there is an electrical problem in the HO2S1 circuit. That means that there could be a bad O2 sensor or something messed up in the circuit. The problem with this is you need a scan tool to be able to diagnose it. Disconnect the O2 sensor, the readings should go to 0V. Then short the sensor, the readings should go to 1V (if its narrowband which i think it is). If both of these occur, then the circuit is fine and your O2 sensor might be the problem. To check the O2 sensor, disconnect a vacuum line and check the O2 sensor output, the O2 reading should go lean (toward 0V). Then spray some carb cleaner in the throttle, the O2 reading should go rich (toward 1V). Sometimes the techs only know how to replace parts, this is especially true if they don't acutally know how the O2 sensors work. If this does not occur, then the O2 sensor is bad. You were correct to suspect that maybe the O2 sensor isn't bad, and the above tests should help you determine what the real problem is. Your gonna want to do the first set of tests first to check the circuit and if those check out, test the O2 sensor. You can change the O2 sensor yourself, especially if you buy an OEM sensor. You might need an O2 sensor socket, which can be found at any autoparts store.

 

i have the exact same roblem with my wifes car. It just started the other day, so i took it in to get tested and they came up with the same code. I just don't want to spend $250 if thats not the problem.

 

Before spending lots of money, CHECK TO MAKE SURE THE WIRES ARE NOT EAT THRU!! My check engine light came on for a couple weeks and I decided to buy a new 02 sensor, before I did, I decided to look at the old one and make sure the new one was similar, in my inspection, my wires connecting to the sensor were frayed and all I had to do was sauder it. These wires are so close to a heat source sometimes and a little saudering of freyed wires will save you money.

 

Hi everyone, been reading thru these forums for a while and time to ask for some help. I work on motorcycles a little so i have a thin foundation of these mechanics but please break things down for me
I see this thread hasn't been touched in a year so thought I'd tag onto it. This is precisely the problem I'm having anyway. I have a scanner

And it came out w/ the same code P0135.
As per what MarcB said I checked the wires and they seem fine. This 98 LX has just over 65K on it. I took off the shield and unfortunately I saw this tiny hairline crack in the manifold



Do you guys think this could be the issue before I throw out another Hundred bucks on a new o2 sensor?

I'm still trying to understand "Agents" advice above, but I don't know what he means w/ 0 volts? or how I would short the sensor, or which vacuum line to pull? clueless [:@] I'm guessing that could only be checked w/ an obd1 tool?
Thanks for your help y'all!

 

If the crack in your exhaust manifold permits outside air to mix with the exhaust gas, then even a good O2 sensor will not send the correct signal to the ECU.

By the way, code P0135 actually indicates a problem with the heater component of the O2 sensor or the circuit for the heater:

 

Thanx for your response ron. I appreciate the specifics of the problem (the heater component) but I guess the best thing to do now would be purchase a new sensor and see if the problem is gone. Hopefully that crack is surface and not all the way thru for now, Maybe I can jb weld it as a quick fix or order one of the cheap $40 header (without the S) in the meantime.
Big thanx for the diagnostic chart- ironically the first check was reset the system and see if it comes back, which it didn't...that is for a while. Checked the wires, didn't see any loose connections.

Just to throw it out there, there WAS a second trouble code (PO304) I think cyl. 4 misfire, when I first tested it. Yuck!

 

This sounds a lot like the frayed wiring problem that a lot of '98s have. Did you check fuse #15 under the dash? It feeds power to the sensor heater. If it's blown you probably have a frayed engine wiring harness. Reportedly, the problem occurs under the intake manifold and you really need to be under the car looking up to see it.

Don't worry about the misfire code unless it reoccurs.

 

mk, i'm out to check the fuse now[sm=smiley20.gif] didn't come across that yet in the hundred pages of exhaust threads i've been reading.
I was worried that I'd have to buy a whole new manifold...was thinking of doing the ex conversion since I'll probably be spending money anyway, but didn't realize it was that tough! So much for wanting to spruce up an LX

As for the reappearing? It has. Took a few days tho. First time, I bought a new air filter (the old one was completely messed up) and reset it. But it came back.

 

For a misfire you should replace distributor cap & rotor, plug wires, plugs. Use only Honda parts for the cap, rotor, and wires. Yes the wires are expensive but they are often the problem.

That crack doesn't seem to be leaking now but it could be trouble later. You can't JB weld it. Either replace the manifold or maybe have someone try to arc weld it.