Repeating CEL? Huh?

[knightpitt]

So, here’s a really strange issue. I’m wondering if anyone has experienced the same. '95 M3. I had been experiencing an intermittent blink of the CEL, so I decided to check it with the pedal trick. I checked it, 1226, Second Knock Sensor. It blinked the same code over and over and over. No pause in between or anything. After 3-4 minutes, I got tired of waiting for it, so I just shut the key off and went into work. After work, I started the car up, and the CEL was illuminated all the time while driving. Dang. So, when I got home, I decided to let the codes cycle through all the way this time and then do a reset. Well, this time, it’s reading 1221, O2 Sensor. Over and over and over. So, I went inside, letting it keep on blinking so that it would finally get to the end. 20 minutes later, and it’s still just sitting there blinking 1221.

Anyone experience/understand/fix this before?

[RogRacer]

You likely have a bad 02 sensor, and a bad knock sensor as well. You can use a Peake reset tool to clear the codes to see if they re-occur, but they likely will.

[knightpitt]

I'd buy that I have both of those issues... certainly wouldn't be a huge surprise or expense. But, what I don't really understand is that the computer just repeats the same code over and over when I try to check the codes. From my understanding of the OBD1 system, it's not supposed to do that. It's supposed to read out the code, then read out 1000, end of all codes, then I can reset it with the pedal again.

Not to be a cheapskate, but I'd rather not shell out for the Peake code reader that will tell me exactly what my car is supposed to tell me to begin with and to reset the codes that the car is supposed to allow me to, if you know what I mean.

[RogRacer]

I've always used my Peake tool for codes and resets, so maybe someone else can chime in.....but I do believe the behavor you describe is normal for the OBD1 system....and the system just endlessly repeats the fault codes. Further, I'm not sure how you clear the codes...but it is possible that removing power for a while will do the trick, but I'm not sure....

[CRYPTiC]

I've experienced the exact same two CEL situations and also have a 95 M3.

The knock sensor fault came up 2 weeks ago. The mechanic told me to ignore it until it comes back again. The O2 fault came up 2 days ago. They did a scan today while the engine was running and the sensor reading came up flat at 0.32V, so it's probably dead and will need to be replaced.

I tried the pedal trick on Sunday and mine also endlessly repeated 1221, so, from what you're saying, it sounds normal despite what Bentley says. I think you can clear the CEL by holding the throttel pedal down for 10 seconds instead of hitting it 5 times within 5 seconds, but I don't have my manual handy.

[donoman]

My O2 sensor also raised a malfunction flag recently. Do you guys advise changing all 4 sensors at the same time, or just the one in question? They are quite expensive and I'd prefer doing one at a time unless there is a reason not to do that. :)

[donoman]

ps. Does the Peake tool do anything that the Pedal Trick (in conjunction with a homemade reset tool) can't do?

[knightpitt]

Cryptic -- it's good to hear that what I've found isn't completely bonkers. I was worried about the ECU. I'll check out the pedal reset... I think that I've tried that before and it didn't work, but I'm not positive... it's not how the Bentley says to do it, though.

donoman -- your car is OBD2 (because it's a '96) and the pedal trick doesn't work for it, therefore you need the Peake tool to read the codes yourself. As for the O2 sensors, if I were you, I'd probably just bite the bullet and do them all... I don't recall if the OBD2 system specificies *which* O2 sensor has gone bad. Also, if what I've read on this forum is correct, your OBD2 car has 3 O2 sensors, not 4.

[Balthazarr]

I'd replace the pre-cat first (2) and see where you are.