Ken King

94 Nissan Altima with occasional start up problems when warm. Almost seems like it wants to load up. Starts fine when cold. Service station says computer says problem
with knock sensor but rarely are these sensors a problem. Nissan dealer says some other problem can cause the knock sensor error but would need to bring it in? Any ideas of what the problem could be?? Car has 202K miles on it and runs great!!!

nucferr

My 1994 ALtima had a sticking EGR valve. I replaced that and seems to run fune (122K miles). The mechanic did tell me that the Knock Sensor was still throwing codes but when he told me how much (he quoted me about $300 installed) I said forget it, Car runs fine with new EGR valve, (Valve was $80)

I have read in this forum that the knock sensor code is the most common and may come in for other issues. Also the cost of the sensor is about $170. The sensor is located above the oil filter on the back side of the engine just under the intake and sound like a bit&h to install.

I guess I will do without one.

jserrano

A bad knock sensor won't give you startup problems. Hell, you can have it totally disconnected and the engine will still start up and run fine. Altimas are notorious for problematic knock sensors. Maybe it was a bad batch or an engineering flaw somewhere. It is the one item that is almost guaranteed to go bad in an Altima. It won't turn on the Check Engine light but a code 34 will get stored inside the ECU.

The knock sensor actually goes bad with temperature. Seems like the piezoelectric crystal inside the sensor distorts with heat and causes the electrical connection to the outside terminals to disconnect.

The most you can hope for is a loose or disconnected knock sensor wiring. Otherwise, there is nothing you can do but replace it.