Hi, new to the forum. I recently bought a 95 4x4 with the cpi. The ses light was on. I read the codes and indicated the bank 1 knock sensor was bad. I had to special order and installed it over the weekend. I disconnected the the battery and no ses light. After about the third time I started it, the ses came back on. Took it to auto zone and same code. I cleaned the electrical connector disconnected the battery and again, about the third time I started it, the ses light is back on. Stopped at auto zone today and same code pops up. Any thoughts? Forgot to mention that no other codes show up but I have a slight miss at idle. I did a tune up with cap, wires and plugs.

 

Have you tested continuity between the PCM/ECU and the knock sensor?

What was the specific code that you pulled?

 

Thanks for responding. My haynes manual does not have an electrical breakdown of the pcm wires. My blazer has the pcm under the hood. I cannot find the gray color wire off the sensor at the pcm. I wasn't sure if the gray sensor wire is a direct connect to the pcm or if it goes to some junction and changes color? I bought a line tracer and was going to use it but I am a little nervous that I might mess something up? I can't rember the specific code right now, but it was read at autozone as a faulty knock sensor bank one. I will go back today and get the code.

 

What is the specific code that you are receiving? I do not show any specific bank codes for the knock sensors in my references.

The wiring diagrams that I just pulled up from Mitchell's shows two sensors (one in each cylinder head) that are run in parallel into the same wire back to the PCM. This wire is dark blue and is on connector B terminal 15 (according to Mitchell's).

Here is a test for the wiring. With the ignition on, disconnect both knock sensors. Using a volt meter (or multi meter set to the DC voltage scale), connect the ground to a suitable ground and probe the connector with the positive terminal. It should read +5V. If it does not, there is an open or grounded condition in the wire.

If there is an open or grounded condition, disconnect the connector from the PCM and test the wire continuity, both from the terminal in the PCM connector to both knock sensors as well as every end to ground. If it is continuous from the PCM to both of the other connectors, and not to ground, then the problem lies within the PCM. If it is open at either of the connectors and/or tests continuous to ground, you have a problem with the wiring harness. It may just be easier to run new wiring if that is the case.

You can also test the knock sensors. They should show ~8600ohms resistance to ground.

 

The code is P0325. Knock Sensor Condition. I think the first time I took it to Auto zone the guy must have read off the code for an import. I have the print out and for Toyota it shows bank one. For domestic, there is no distinction. I will update on the sensor wire test. I also noticed that one of the possible causes could be low fuel pressure. I do have a very slight miss at idle. No other codes are present. Thanks

 

Here is the DTC listing for the newer SCFI engines:
P0325 - Knock Sensor 1 Circuit
The diagram for your truck will be different, but the rest of the trouble shooting should hold true.

 

I was able to disconnect the sensors and test the wire. No voltage present for either one. I would like to by pass the wire at the pcm, but I have four connectors at the pcm; red, blue, gray, and black. I pulled all connectors at the pcm and the #15 wire slot is not used. I don't know if I am looking at the right one? I will keep at it. Thanks I will keep trouble shooting.