Hey guys,

I was driving to work this morning and my CEL blinked a few times. I freaked out a little (considering that I heard a blinking CEL is much worse than a constantly lit one), but then it stopped blinking. Didn't turn on again till after I had the guy at Advance try to check it (he said that his device wouldn't connect with my car) but then it stayed lit from that point on. I then take it to Autozone and that guy's device connected and the read out said P0155. The light has stayed on since the first guy checked it at Advance.

P0155 according to the little receipt from the guy at Autozone says this:

Definition
BBHO2S21 heater circuit fault

Probable Cause
BB1.- Open or short circuit condition
BB2.- Poor electrical connection
BB3.- Faulty H02S21

I have looked and looked and looked on this site and have not been able to find a matching Code in all of the threads that I looked through when I typed in this code (or any of the key words from the descriptions). Going to call Mazda tommorow and see what they say, but I was hoping to get some information from you guys (who I trust infinitely more than the guys there).

I did put this information into google and found this explanation on a general Mazda forum....

"Info taken from the 247 boards...

Mazda Specific OBDII Trouble Codes
These codes are as of 12/04, so they should apply to all '96 -'05 Mazdas. Trouble codes less than 1000 are generic OBDII codes and apply to all OBDII compliant vehicles as a minimum Federal Standard.

It should be noted that in '08 all manufacturers will be required to move to the CAN protocol, and movement has already started in that direction. For example, the Mazda 6 and RX-8 are already using CAN. This means that scanners previously used for OBDII likely will not work in these vehicles."

Scrolling down it says this for P0155:

"P0155 O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)"

I should add that I did a search when I got to work earlier and found that a temporarily blinking CEL is most likely triggered by a simple misfire. I should also add that Mazda said that I was due for new plugs the last time that I had the car in for an oil change (I didn't have them change the plugs cause I can do it myself for far less than $270).

Any help is much appreciated.... Thanks!

 

you have a bad O2 sensor

 

that code is in relation to your O2 sensor (oxygen ) in your exhaust. O2 sensors are heated via electricity to bring them up to operating temp within seconds of starting your car, this way the PCM go go to closed loop quicker. Its all emissions related. If your car is not under warranty I wouldnt worry about it. An o2 sensor heats up in around 30 seconds by itself. Shouldnt cause any drivibility issues.

 

Maybe, but I wouldnt condemn the sensor itself if thats the only code he has. If the sensor isnt functioning he should be getting other codes. Only way to tell is to get a scan tool on it to check the o2 function.

 

Well that is a relief. I have had the Cat replaced already under warrany and I was hoping that it wasn't that. I have 3K left on my warranty and I will just have them give it a look. I am changing the plugs this weekend and so hopefully that will eliminate any more misfires (if that is indeed what that was earlier in the day). Thanks for the information guys!

 

I thought that there was a way to check the codes yourself. Some kind of trick that you can do with your keys to get the CEL light to blink in a certain pattern that will tell you what exactly is going on. Is there such magic with these cars?

 

No magic key tricks with OBDII cars. Blinking CELwas OBDi (pre '96).
Blinking cel is a misfire. usually the plugs.

Only way to check codes is with a scanner. You can pick up a code reader for like $20.