I have a 1994 sr5 3.0 v6 a/t 4x4 I recently had a new waterpump/timingbelt replace done on my truck Shorty before install the check engine light went on and I noticed a difference in its running, lousy acceleration ect. The mechanic got code # it is saying knock sensor needs to be replaced. Replacement cost by mechanic is 200.00 up I have a couple of questions on this issue. 1 What will happen if it isn't replaced will it damage motor ? 2 How hard is it to replace? I am not a mechanic I am not afraid of trying to replace it, I just don't want to screw it up any further. Its just costed me 600.00 for the water/pump/timing belt replacement which was going rate around here. I had asked the mechanic for a truthful assessment on the truck as a whole he said engine/transmission are fine but... needs shocks and 2 frount axles Cab is in fair condition needs fender, bed is kinda beat up dents scratches ect Frame is fine normal surface rust in areas I am not rich, I have had the truck going on 9yrs The mechanic said he wouldn't put too much money into it drive it till it dies Any advice would be appreciated thanks I don't care about dings and dents or scratches and I do like this truck but I don't need a money pit either

 

Do a search here for Code 52 -- which is almost certainly the code you got. It means the ECU has "lost contact" with the knock sensor, and as a result dramatically retards the timing to save the engine. Retarded timing= lousy running.

While your mechanic is pointing in the right direction, it almost certainly is not the knock sensor itself; they are very tough. The most likely problem is the "pigtail" from the knock sensor to the connector on the "outside" of the intake manifold. The pigtail is in a hellish environment, and just doesn't last 20 years.

BUT: when you do your search, you will find many who have replaced both the pigtail and the sensor, but still have a problem. Probably due to damaged wiring elsewhere, but where?

To get to the pigtail (and the sensor) you have to remove the lower intake manifold, which means you have to remove everything above it. I can do it, so it certainly isn't that hard, but I don't know it's the job you want to be your first.

If it was me, I'd read through the manual, replace the pigtail, and hope it will do what it probably will do: clear your code. Then replace the shocks and the front half-shafts (much easier) and you'll be good.

 

If he is only charging you $200 to replace the knock sensor that's a very good price. Most of the time the issue is the wire that runs from the sensor to the main harness located on the drivers side cylinder head. Unfortanitly this is a pain to get to and requires the hole intake manifold to be removed. It's a pain.