The malfunction indicator lamp of my 1996 Civic DX (auto transmission) is on. The car has a little over 90K miles on it. I bridged the two pins in the service connector with a wire and read one long flash by the MIL. According to the Honda Service Manual, probable causes for ECU Error Code 1 are primary O2 sensor short or open circuit, fuel pressure, bad primary O2 sensor, short in wire to ECM/PCM, and bad ECM/PCM. The Honda manual says to troubleshoot in that order, more or less.

I've read that it is foolish to automatically change out the O2 sensor and that one should do the diagnostics properly. However, I don't have the scan tool they suggest for checking voltages and I'm not sure how to check fuel pressure and all the things that affect it. The engine is infrequently rough at idle (misfire?).

Since the vehicle already has 90K mi on it, is it reasonable to take a chance and just replace the O2 sensor? Is it important to get more information by capturing the DTC code(s)? Thanks.

 

One short flash is code 1, but one long flash is code 10. Unplugging the IACV should throw code 14 (1 long, 4 short flashes), so that you can see the difference. Code 10 is a problem with the IAT sensor circuit.

You can also take the car to an auto parts store that pull codes with an OBDII scan tool free of charge.

 

Thanks, Ron. Yeah, I don't really know if it was one long or one short. I'll try an auto parts store tomorrow.

 

Dang. I just read on another site that auto parts stores won't let you borrow a scanner in California and Hawaii anymore. It apparently is against some regulation.

 

-92-00 CEL codes;


click link, each fast blink = 1 and each 1/2 sec blink =10

 

I don't know one way or the other on that but I do know not to believe everything I read on the internet. You should call a store to confirm that. It's better to use an OBDII scanner because it gives more detailed information than the blinking light method.

Whenever you have an O2 sensor code on a 1996 the "fuse 15 problem" should be ruled out.

 

Fuse 15 was OK. I got a free DTC scan at Aamco (AutoZone wouldn't do it). P0135 was displayed. Helm manual says it indicates an electrical problem in the primary heated oxygen sensor, and on pages 11-157 & 8 they explain how to troubleshoot it. I have an old analog multimeter, so after I do my taxes I'll start the process. Is there a particular socket (3/8" drive) that removes the O2 sensor from my '96 Civic better than others? Thanks for your help. Sorry for the elementary questions.

 

One more thing. If I end up buying a new sensor my local parts shop has a Denso 234-4099 sensor for a good price, which is a direct OE replacement. Is that a good choice?

 

Denso is one of the two actual parts manufacturers for Honda's Electrical systems, so i would say thats a go.

 

Thanks guys. The job is done. MIL is reset and hasn't come back on ... yet.

In case some beginner reads this later here are a few details not mentioned in the above posts. After the OBD II scan showed an error code of P0135, the electrical troubleshooting shown in the Honda Service Manual p. 11-157 was followed. My sensor had infinite resistance between terminals 3 and 4, thus it had to be replaced. I "borrowed" the oxygen sensor socket set from Autozone. That is, you buy the tool, but when you return it you get your money back. They give you 90 days to return it. Great program. Too bad the OBD II scanner is no longer included among their loaners tools in California (verified by Autozone). The car repair lobby didn't like it and our governor agreed with them. I took off the oxygen sensor cover (p. 9-12). It may not have been necessary, but it made it easier to use my socket wrench. Denso 234-4099 did not require any splicing of wires. Denso included a tube of anti-seize grease, which was nice. I used it on the sensor threads as well as the bolt threads for the cover.

Regarding reading ECU error codes via the Service Check Connector (p. 11-81), if I'm not mistaken the MIL flash is actually indicated when the light goes off. That is, the MIL goes from on to off to back on. The duration that it is off indicates whether that digit is a one or a ten. My MIL flashed off once very briefly (seemed like less than 1/2 second) indicating an ECU error code of 01 (not 10), and that was later confirmed by the OBD II code of P0135.


Any recommendations for an inexpensive OBD II scanner? I read that CAN scanners are required for newer cars. Is CAN backward compatible to a '96 Civic?