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1999 toyota tacoma
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Discussion Starter #1
I have a question. I have a 1999 Tacoma V/6. Has anyone tried to unplug the knock sensors and fool the ECM into thinking they are hooked up. I have been told that a cold engine piston slap is causing my ECM to turn on the SES light. I have checked the circuit and the sensors the way the book says to, and everything seems good. So, before I buy a new ECM or tear the engine down, I was wondering if a resistor could be plugged into the line going to the ECM making it think the sensors are plugged in. If so, what size resistor should I try?:confused:
 

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Former Toyota/ASE Master
325i
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1,078 Posts
No, it won't. The knock sensor aren't resistors, they are piezo electric crystals. Piezos make voltage when pressure is applied to them. In the case of a knock sensor, this pressure comes from the sound of predetonation. The computer is tuned to look at the ac wave made by the sensor and determine when these knocks are happening and to retard the timing when a certain threshold is met.
So, for this reason you can't plug anything in that will mimic a knock sensor. Besides, you need it working properly to allow the computer to run the engine efficiently. Personally, I've never seen a knock sensor go bad. Piezos are very rugged, and they are solid state. They just don't break (at least on Yotas). Every knock sensor code I've seen has been either wiring or the computer, the former being the vast majority. Knock sensors make an AC signal, which means that the wires have to be shielded. If the shielding breaks down, the signal leaks out and goes to hell. Given that the wire lives in the center of the bank of your engine (lots of heat and vibration), it's probable that wiring is the cause of most problems.
Hope this helps. BTW, what code(s) do you have? Any others besides 330 or 325? Both?

Furthermore, the condition for the computer setting the knock sensor codes is a complete lack of signal. Excess knocking (like the piston slap idea) won't. So for the computer to store those codes, you would have:

-A dead sensor, or a sensor not screwed tight into the block
-Broken wire or shielding
-A computer that can't see the signal.

Hope this helps. BTW, what code(s) do you have? Any others besides 330 or 325? Both?
 
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