spookiedog

Help
I have a 98 4Runner, Auto, 4wd, Supercharged, non-cali truck.
The engine light has come on and the diagonistics say it is a bad knock sensor. The Toyota dealership says, "Can't tell which of the two knock sensors are bad, need to open it up to find out which one is bad". This requires removing the supercharger and cost one heck of alot ~$1100
Knock sensors seem to be $189 each, so pretty frustrating, they can only tell when they have it opened up. Side note: they do have the knock sensor wire in the quote, curious, since I have heard that is a problem point...
Any suggestions or comments welcome, price, alternatives,do-it yourself?
Have replaced a 7MGTE before, no prob, of course not having a check engine light makes it easier.
Also installed the supercharger myself, but I am also mechanically inclined. (Way too many beaters in my life)
Would like to know what causes a knock sensor to go bad (bad childhood?) Why are there two, according to the toyota dealership? Why would the check engine light not know which one is bad? Who designed that check engine light (stupid question, I know) but I would like to meet them in an dark alley.

Thanks in advance any help I could get, or at least grammer corrections
Kevin

Brian R.

I have heard that knock sensors rarely fail and it is almost always the wiring. Take both connections apart and snug up the connections. While you have them apart, clean them with electronic cleaner.

Therre are two sensors because you have two banks of cylinders. A 4 cylinder engine only has one.

The CEL only knows it is getting a bad signal. Probably, the two sensors feed the same input into the ECM so there is no way to tell which sensor is bad.

You can check them if you wish by testing continuity between the sensor contact and the sensor body. There should be no continuity.

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spookiedog

Thanks for the advice. Will be buying a factory service manual this week and digginig into to see how hard the knock sensor wires are to get to.

Thanks again
Kevin

Brian R.

If you only need to access the connector for the harness, it comes out the front of the engine from underneath the intake manifold and you can reach it without any work. To access the sensors and their connectors, you will have to remove the intake manifold and the No. 2 timing belt cover.

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spookiedog

Brian,
Thanks for you help, I got it fixed and replaced the timing belt and water pump (was leaking, minor). Ended up replacing the wire and all seems well now.
Bill came to $1100 which normaly I would have done for myself, but considering this is the first thing to go wrong in 81,000 miles, I don't feel to bad.
Thanks again for your assistance.

Brian R.

You're welcome

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