1988yotapickup

Have the check engine light on. It only comes on after I put the truck in drive and h it 25-30 miles per hour. Have both diagnostic codes 51 and 52. engine runs great and there are not other issues with the truck. any suggestions?

I have a new knock sensor in hand but dont think thats the problem since it only comes on after I hit 25-30mph.

scope103

Welcome to YotaTech.

I'd start by looking at the manual. http://web.archive.org/web/201211190...85diagnosi.pdf (This manual is for a '93, but the diagnostics are the same, except for the connector.)

Then I'd take a few minutes with "search." Code 52 is probably the most-discussed item on this forum. But to give you the executive summary: it's definitely a knock sensor issue, but it's probably not the sensor itself (those are very tough). Your problem is almost certainly caused by a bad "pig-tail" that connects the sensor to a connector just outside of the intake manifold. It is a system that requires the ECU to read a subtle voltage in an electrically noisy environment, so these issues can be difficult to resolve.

RAD4Runner

Second that^^^ Toyota components are usually bullet-proof, so do not suspect them right away.
Problems are often caused by how they are wired or put together. Check this first. Less expensive to check and fix than replacing expensive parts that are not broken in the first place.