Good morning all:

This vehicle is the 94 EX that has a 93 LX 1.5 liter transplanted into her. All is going well other than a check engine light. I have read the code as a 43, and I looked in the manual to see that it is the 02 sensor (thanks Ron) but I have a couple of questions. 1) The code doesn't throw until after driving for 3-4 minutes. Does that mean that it has reset each time the car is shut down and then diagnoses itself bad again after driving? 2) Is it normal for this particular code to have a delay before illuminating the check engine light? 3) Given the delay, is this indicative of anything that is a 'been there done that' for anyone? 4) I may have loaded the O2 sensor during the time when we were trying to figure out the MAP sensor/harness problem. Is it possible to clean an O2 sensor?

Of course, any and all help appreciated.

Ed Fisher
Dallas, Tx

 

It's very common for the ECU of 5th generation Civics to lose CEL codes after the key is turned off. The ECU will not re-throw the CEL code until it receives two fault signals.

Is the CEL code for the O2 sensor itself or the heater element? Are there any engine performance problems associated with code 43?

 

The O2 sensor normally doesn't work until it has a chance to warm up, so yes the delay is normal. Every time the engine is started, the ECU ignores the sensor for a few minutes to allow it to warm up. Then the code is set if the readings are not as expected.

With the engine cold, unplug the sensor and measure its heater resistance between the two wires that are the same color. If the heater is open circuit the sensor is definitely bad and needs to be replaced.

 

Ron:

I am not sure how to tell if the code is for the heater or the sensor. I don't seem to have any performance problems with the code, but I haven't gone through a full tank of gas yet to check mileage.

MK:

Do I understand you to mean that when I unplug the connector upstream from the O2 sensor itself that there will be two wires that are the same color there, and to look for identical colors/heater wires there? If open a bad O2 sensor because a heater is bad? If any resistance then the O2 sensor is likely good?

Thanks for the replies and the help.

Ed

 

My mistake. Code 43 would only indicate a sensor not heater element problem.

 

Oxygen sensor replaced this weekend and the car is running beautifully. My fuel consumption was disappointedly at 26+mpg and I fully expect it to return to the 36-37 range now. No codes, smooth idle, and good acceleration, at least as good as the 1.5 liter can put out. Thanks for all of the help.

 

After engine replacement, be sure to set the spark timing with a timing light. Having it off can really hurt your gas mileage.

 

Also reset the ECU after the O2 sensor replacement to speed up the ECU relearning process.

 

MK and Ron J.

Done and done (timing set and backup fuse pulled for quick learning). Thanks fellas. BTW, after going about 75 miles my fuel gauge hasn't gotten below the full mark yet. I think she is back!

I really appreciate the help, always.

Ed