Check engine light came on.

[Highway_Star]

I went to autozone and used their scan tool, found that there was a p0325 code (knock sensor). This is the second time that has happened (didn't replace it back then, just cleared the code and turned off the CEL, that was a year ago).

 

When looking at the conditions that set the code, I noticed that the long term fuel trims were at negative 10.8%, meaning it was leaning out the fuel mix a lot.

 

Could a very lean mix somehow cause a knock sensor code? Just want to know before I go and buy a new knock sensor if I actually need one.

 

*edit* forgot to mention it's a 1999 Legacy with the 2.2 SOHC.

[nipper]

Just replace the knock sensor. The code only gets thrown if the sensor malfunctions, not if something is beyond it's capability.

[Highway_Star]

Thanks, I know that the fuel trims are controlled by the O2 sensor, I just needed to know if a bad O2 could cause conditions that might fool the ECU into thinking the knock sensor went bad. Looks like I need to replace 2 sensors now.

[wtdash]

On older OBD1 cars a bad KS would cause 'limp mode', but I'd think the car would run Rich not Lean, for safety.

 

If you're over 100K the O2's may be due - should be 2.

 

GL,

TD

Edited October 13, 2011 by wtdash

[Rooster2]

On older OBD1 cars a bad KS would cause 'limp mode', but I'd think the car would run Rich not Lean, for safety.

 

If you're over 100K the O2's may be due - should be 2.

 

GL,

TD

 

I think that a bad KS results in "limp mode" computer function, that retards engine timing to prevent detonation (Ping). Does the KS do this, or affect rich/lean mixture instead?

[wtdash]

I think that a bad KS results in "limp mode" computer function, that retards engine timing to prevent detonation (Ping). Does the KS do this, or affect rich/lean mixture instead?

 

This is for OBD1, which may not match an OBD2 system.

 

From Legacy Centrall BBS - How to Read Trouble Codes From the ECU:

 

 

Code:22

Item: Knock sensor

Diagnosis: Abnormal voltage produced in knock sensor monitor circuit

Fail-Safe <limp> Operation: Sets in regular fuel map and retards ignition timing

 

 

I don't know what 'sets in regular fuel map' means, but it does affect fueling.

 

TD

Edited October 14, 2011 by wtdash

[Fairtax4me]

That's if it goes into limp mode. Just because the code is present doe not mean the ECU is in limp mode. There are several ways a knock sensor can fail and cause a code to set, but the same code sets for all of those failures.

 

Inspect/replace the knock sensor. Deal with the fuel trim issue if it's still around after resetting the ECU.

[Highway_Star]

I replaced both sensors, the fuel trims are back to 0.0%.

 

That o2 sensor is in an awkward place, had to rent a crows foot tool to get it out since there was no room for the socket type tool.

[brus brother]

I replaced both sensors, the fuel trims are back to 0.0%.

 

That o2 sensor is in an awkward place, had to rent a crows foot tool to get it out since there was no room for the socket type tool.

Did you replace O2 sensors (are there 2 as stated earlier?) and knock sensor or just O2 sensors?

[Highway_Star]

I replaced the knock sensor and the pre-cat o2 sensor (I didn't see the other o2 sensor). Like I said earlier, the fuel trims are back to normal and it has a tiny bump in horsepower.

But today I could feel the engine lose power and see the RPMs drop when the new knock sensor retards the timing when I give it a little throttle while the engine is cold.

 

So now I've either uncovered a new problem with the engine, or I installed a bad sensor (it said "made in turkey" on the box), I'm going to take a closer look at the old sensor.

[nipper]

Well thanksgiving is coming...

 

One other thing, since it was fine then started loosing power, a partially clogged cat. Get yourself a vacum gauge. If it starts out high then slowly drops you have collapsed/clogged exhaust system, which means a cat.

[Highway_Star]

I know it's not a clogged cat, they happen kinda gradually, this happened immedeatly after putting in the knock sensor.

[Caboobaroo]

I recently had a bad knock sensor right out of the box that was brand new. Same deal, car came in with a P0325, replaced knock sensor with a new one and the check engine light came back with the same code. Replaced it with another one and it was good to go.