CEL - Code 28, knock sensor. Help?
 

Hey guys, I need some help with a Check Engine Light code and resolution. I have to pass a federal inspection in the next 31 days, and a CEL probably won’t help much. I did a search and found some info on replacing knock sensors, but I jut have a few followup questions.

The code shows 28, Knock sensor 2 (LH): Abnormal voltage in knock sensor monitor circuit. Lucky me, the harder one to get at!

Here are my questions for you:
- Do I absolutely have to replace my knock sensor, or will replacing it just have the new sensor show a voltage error?
- Can I just reset the code and hope that it doesn't come back? Never done that before, but I found procedures on how to.
- I damaged the connector on the positive terminal of my battery the other day. Would this CEL be related at all?
- I hear that you’re supposed to, but is it mandatory to replace both knock sensors at the same time?

I just brought this car up from the US. She’s used to gas from her old home, but I was sure to use premium (higher octane) here with a shot from the bottle of fuel additive that the previous owner gave me. The gas was in the tank for 7 days before the CEL came on, so it may be unrelated.

I just need to get the car past inspection, and that would be difficult with a CEL showing. I hope that I don’t have to replace the knock sensors, but I will do it if I have to. Any info you guys can provide will be most appreciated.

1) The problem could be with the wiring that leads to the knock sensor...you'd have to test the sensor itself to determine that.

2) You could, but chances are it will return shortly.

3) No. A bad battery connection would cause multiple voltage problems, not just one.

4) No, you don't have to do both at once.


Hope this helps.



Dave

Have a look at the knock sensors. Both of mine were cracked but didn't throw an error code.

OK, home now. Here's an update. I can hear a very noticeable TICK TICK TICK TICK when the car is running. It's coming from the general vicinity of the knock sensor that throws the code 28.

What can I do to fix this? Replace the knock sensor?
If I replace the knock sensor, won't the sensor just detect the engine knock again? (PS: I don't know anything about knock sensors).

Just need to get something done about this right away, so all help is welcome.

When I clear the codes, I just get a 28 again right away. If someone can confirm that my problem will go away by replacing the knock sensor, I can get one ordered today.

What if it doesn't fix it, then what?

Why wouldn't it fix your problem? You are running premium gas, right? So it can't be bad gas. The ECU is telling you what the problem is. Replace the sensor!



Dave

PS all Subaru's have a slight tick when running....it's normal.

Are you sure the tick is not just the injectors?

Knock sensor odered from subaruparts.com. Thanks, guys.