Problem- 99 Impreza OBS with a cracked knock sensor that has been throwing codes every time it sees a little moisture.

 

Temp solution- pull out cracked knock sensor, spray with a conductivity promoting aerosol (PB has even worked), replace knock sensor and watch CEL and hesitation disappear.

Might work if the sensor is freshly cracked. After a couple times getting moisture in it the sensor element corrodes and then there's no fix-in-a-can solution. 

 

Other option for short term is to solder a couple resistors together to get around 580k ohms. Cut the connector end off the sensor and crimp it to one end of the resistor, put an eleyet on the other end and bolt it to the block. Shrink wrap it or liquid tape it or plasti-dip it to keep it from shorting to the block or getting moisture on it. 

Yikes! Do not fool your ECU out of limp mode with resistors. If you use heavy throttle up a steep grade, or just accelerate hard, the engine will ping a bit by design. The knock sensor retards the timing until it doesn't ping, that's part of how they adjust for maximum fuel economy and efficiency. However, if the knock sensor is missing you'll get bad pinging and risk melting the pistons.

 

If the sensor is going bad, replace it! If you have to deal with limp mode and hesitation, suck it up, better than ruining your engine by letting it ping.

Was supposed to be short term like 2 years ago on mine. It worked so I left it that way.

This sensor has been cracked since I bought the car 6 months and 15k ago, and I've been doing this for probably 4 months. I also have a cracked one on the '99 Forester I have used the same method on, until the water pump gave up and she bent SIXTEEN valves.

 

As long as I don't smash through any lagoons they remain functional.

Knock sensors are pretty cheap and easy enough to replace. I've bypassed one just to get the car driveable, but it knocked terribly when I tried to pull a trailer with it. So it's worth it just to put a new one in to protect the engine from damage.

The way I see it, it's still functioning properly, it's just getting a low knock sensor signal CEL when water gets in and effectively shorts the signal. I had the codes read after I reset it the first time to be sure, it was clean. I've never noticed any pinging at all, believe me I'd have shut it down immediately. I learned my lesson setting the timing too hot on a SBC.