Knock sensor error codes P0325 & P0330

I posted this in the first gen forum yesterday, however I am re-posting here as this forum is more applicable.

Help. I have a '96 4x4 Tacoma SR5, 3.4 5VZFE non California model (no EGR system). with error codes P0325 & P0330.
Have changed both knock sensors (Matsushita from Oreilly's) and lower harness (from Toyota). Still have the error codes. Tested the wiring harness for shorts to ground and continuity. Bypassed the wires from the lower harness connection to the ECM connector. No change, still have the codes.
Is there anything else in the system that could cause the P0325 & 330 codes?
How to test or diagnose if the problem is with the ECM?

Thanks for any help and suggestions.

 

The knock sensor is a piezoelectric sensor that in a normally running engine oscillates at a steady frequency. This oscillation generates a steady low voltage signal that the ecu monitors as a no knock condition. When knocking is sensed, the oscillation changes, the voltage signal then changes and the ecm retards the timing or does whatever it has to do to eliminate the knocking(pinging). I would carefully clean and check all connectors, retest the resistance of the harness, not just a beep or light continuity test. Your codes indicate a "circuit malfunction" . Do you hear pinging while driving, especially up a steep hill? It may be that it is indeed pinging for some reason. Why did you change the harness originally? There should be specs on the senors you used that indicate the expected resistance. If not can you compare the resistance of the ones you removed to the new ones? That may reveal something. Sometimes aftermarket parts are just not the same. Since you have it on both banks it must be something common to both circuits. Maybe the connector at the ecu is dirty or not seated fully or some pins are bent?

 

Hi Troyken, thanks for your reply. I originally changed the knock sensors and lower harness due the ECM codes. I checked the knock sensors that I took out by lightly tapping on the block near the sensor and they did produce a voltage but decided to change them and the lower harness due to the difficulty of getting to them. Also changed the valve cover gaskets, plugs, wires, etc.
If I reset the code and drive the truck. The code does not come on until I put the engine under a light load, 3rd gear acceleration. While I don't hear the pinging, it should happen when lugging the engine. The code seems to come on quicker when the engine is hot verses when the engine is cold.

When you say "circuit malfunction", are there any other components related to this circuit? I saw something online about the EGR circuit could play into this but my truck does not have an EGR valve.

I checked the ohms for each wire in the main harness to the ECM and also ohms to earth with a good Fluke meter. All checked good. I don't see any bent or corroded/oxidized pins but will look again carefully. I'll go back and check the harness shield pin to earth and see how that reads. Other than that, I don't know what else to check besides pulling the ECM and sending it out to be checked or buying a replacement. This is getting expensive and I'm still not sure what is causing the problem.
It'll be a week or so before I get time to work on this again.

Again thanks for your help. It's greatly appreciated.

 

I think other than connectors that is a direct run circuit to the ecm. I wonder if you can fill up with premium Hi- test gas and see if it makes a difference. It sounds like you may be pinging and the sensors are "hearing" it. Are you using lower grade regular gas? How many miles are on it? Sometimes the pistons get a lot of carbon build up and that causes detonation. Is the engine running hotter than normal? That will contribute to the issue too.

 

Hi Troyken, Thanks, I have tried premium gas. Forgot to mention that I sent the injectors for cleaning and flow testing. They were actually quiet clean when I pulled them out and flowed quiet well. I expected them to have more carbon on them, with amount of miles on the truck - 265K. I can post the before and after flow results if needed. Thermostat was changed about six months ago, stuck open, was running cold. Now the temperature is normal. The check engine light was on before the thermostat change, seems has been on for quite a while, my son's truck. Will do some more testing on the lower harness and knock sensors, should be able to get a voltage reading by lightly tapping on the engine block. Will confirm that each sensor outputs a similar voltage. A little concerned about the replacement sensors from Oreilly's. They appear to be made by Matsushita, same as the original ones that came out of this truck. Although, I'm not sure if the one's that I took out are the originals due to the age, miles, and not knowing the repair history. It could have had Denso brand knock sensors in it originally, although I can't imagine that the two are not interchangeable. I noticed the intake has been off previously.
Thanks.

 

I'm getting out on thin ice here but... It seems that when an engine pings, two things happen to deal with it:
1. The ecu retards the ignition timing
2. The ecu adds fuel.

Your comment about the fuel injectors now makes me wonder.... is it pinging from a fuel related problem , pressure or flow from the pump maybe if the injectors tested good? Maybe you need to have a mechanic (or you) test drive with a scan tool connected to see what the fuel trims, timing and coolant temp look like. Maybe a subtle vacuum leak is causing a lean condition making for a hotter than normal burn and causing detectable pinging?

This is a tricky one for sure.

 

Hi Troyken, I was thinking about testing the fuel pressure. Actually the fuel filter looks original, will change that as well. I don't think I have a vacuum leak, checked all the hoses and replaced a few. Intake gaskets are all OE or Mahle. Repaired rat chewed wires to the VSV that controls the idle up function when turning on the air conditioner. This all works correctly now, as well as the idle up function when turning the steering wheel.
Will do more testing and post the results in a couple of weeks, busy with work.

Thanks for all your help.

 

What are your thoughts on aftermarket fuel filters vs OE? I had issues with an '86 4Runner, caused by an aftermarket fuel filter.

 

I'm always leary of aftermarket stuff these days, but If it fits, doesn't leak,and runs ok it should be ok. Good luck with it.

 

Hey Kevin, did you ever figure out what was going on? I’ve got a 1997 with the 3rz and just started getting the p0325 code. It happened after my negative battery cable slipped off while I was driving. I’m really hoping it’s not computer damage, but I’d rather figure it out here than pay a diagnostic fee at the dealership.

 

hey Austin, sorry for the really late response i did not see the email in my inbox till now. I did end up finding what was wrong with my truck. The computer could not get a reading on the Oreilly's knock sensors. I did end up changing the ecm for one i found on ebay along with finding a fuel testing kit that works on Toyota Tacoma hoping it was one of those and not the knock sensors. I i ended up replaying the knock sensors with factory toyota and have not had a problem yet. Im not sure if losing a battery cable would damage the ecm but anything is possible. The knock sensor could have failed when the cable came off. let me know if you have any questions i will try to check my email more often