Looking for advice on a 2004 Lexus SC430 with an ongoing knock sensor circuit issue that is still not resolved.

Current codes from the scan:
- P0325 — Knock Sensor 1 Circuit
- P0330 — Knock Sensor 2 Circuit Malfunction

There were also pending O2 slow-response codes, but the main repeated issue has been the knock sensor circuit codes.

What happened:
The car had a major loss of power and would barely go past about 30 mph.
Steps already taken:

1. Full scan was done
The scan showed current P0325 and P0330 knock sensor circuit codes.

2. Intake / vacuum leak issues were found and repaired
A smoke test found multiple intake / hose leak problems. Some of the old hose repairs were badly hacked together. Those leaks were fixed first.

3. Knock sensors and broken connector pigtails were replaced
Both knock sensors were replaced, along with the broken connector ends / pigtails.

4. Wiring was checked
Mechanic says the wiring from the knock sensor side to the ECU checks out clean, but the code still returns after the engine gets hot.

At this point, the mechanic is suspecting the ECU / ECM.

Extra info:
We also spoke to an ECU repair guy, and he said this is weird / not a normal repair case, and they do not have a repair service for this kind of issue.

So I’m trying to figure out:

- Has anyone seen P0325 / P0330 return only when hot on an SC430?
- Has anyone had the issue turn out to be the ECU, or was it still the harness farther back?
- Are there any known SC430 / 3UZ-FE weak points in the knock sensor circuit that could cause this?

Any input from someone who has actually dealt with this on an SC430 would be appreciated.

 

That's a tough problem to have. I would tend to agree with your ECU repair guys thoughts, the ECU generally don't fail unless you're in extreme heat or water gets in there. What kind of mileage/condition/service history do you have with this car? Was the 1st mechanic someone who normally works on these older SC430 and LS430 platforms? Does he have a set of the Lexus Factory Service manuals? I'd really take a step back and come at it from a 1) what happened 1st and why would that happen mechanically. Just saying it was your old vacuum system that caused a sudden loss of power is weird. These car's aren't just normal Toyota's, they were $80,000 luxury convertibles and now they're 20+ years old. Hell, even Lexus dealers don't have anyone in their shop that has experience with these. They'll do whatever the Toyota system says to do, but that's a far cry from a wrench that has years of experience.

 

Let me clarify the sequence better.

1. The car started not running as smooth as before, and I had a lot of intermittent hesitation.
2. One cylinder issue was repaired.
3. 10 days later car would not go over about 25 mph.
4. At the shop, they found hose/vacuum issues. Those were repaired.
5. They also replaced the knock sensors and the pigtails/connectors.
6. After all of that, I still have slight hesitation, and I still get knock sensor circuit codes.

So now I’m trying to understand:

• if the hoses were fixed
• and the knock sensors were replaced
• and the pigtails were replaced, and the wiring/circuits to the ECU tested clean

why would I still have slight hesitation and knock sensor codes?

Would the remaining hesitation still make sense from the knock sensor issue alone, or does this sound like there is still another problem being missed?

I do not think it is transmission.

 

@deardave -- I put your entire post #3 in google and although we know google doesn't always have correct information, maybe it presents another perspective?

 

Maybe someone else with more experience can help you...The (3rd Gen LS) LS430 has the same engine and there's way more posts/experienced mechanics on that forum, they may be more helpful. All I'd say is that Knock sensors are solid state peizoelectric sensors. There's no reason for them to fail unless water caused corrosion on the leads or someone/thing damaged the wires to them. To replace them just because they're showing a code in the computer isn't the correct corrective action because something caused them to fail or to produce code in the 1st place. You/your mechanic needs to figure out what's actually causing the 1st issue (be that Knock sensor value, or your pending O2 fault) If you've been driving your car with a bad O2 sensor for lots and lots of miles you may have damaged something. If there was a lot of air (like 1/4 inch hole sized void) leaking into the intake via the vacuum system (past the MAF sensor) and the car was getting more air than it thought your long term fuel trims (LTFT) would of been wild like 15-25% over nominal, the car can only trim so much before it get into a permant lean condition. These conditions for many many miles can also cause damage. I'm just saying I'd trust the car's sensors to tell you what's actually wrong and not just blame and replace the sensor. Also an active knock sensor fault, or active O2 code can cause the car to go into limp-mode to protect the engine leading to your sudden loss of power. Sensor fault when "hot" probably just means there's a certain number of uncorrectable knock events that need to occur before a fault code is thrown. It's common for engines to knock once or twice on start up, but for it to happen constantly then tells the computer that there's something more going on.

I really do hope you get your car fixed get many more miles out of yours. If your O2 sensors have been bad or thrown codes in the past I'd start by replacing the bad ones 1st. Then just checking the entire intake system (past the MAF) for any damage/leaks. Then borescope the cylinders just to make sure everything looks good internally. Maybe your fuel pump is just about to fail causing lack of flow and multiple knock events? I wouldn't replce more parts without getting a positive diagnosis.

 

@deardave Were the knock sensors replaced with OEM or aftermarket parts? If aftermarket sensors were used, then that may be causing the problem. I know our cars are sensitive to those kind of differences (I had a similar issue with non OEM coil packs). If you used OEM sensors, then I would check your 22 year old ECU for issues. By the way my 2002 with ~185,000 miles on the odometer still has the original knock sensors, but I did replace the pigtails and broken connectors.

 

non oem

 

Just wondering what's your mileage?

If you want to replace your knock sensors with OEM, here's info on my go-to places.

They offer Free Shipping and No Sales Tax for out-of-state customers.

If Treasure Coast is near you, maybe go thru them even if you have to pay sales tax, they have the cheapest price. I looked at some of GA's online parts depts and they didn't have as good of prices as these below:


Ignition Knock (Detonation) Sensor

Part Number: 8961530080

https://parts.treasurecoastlexus.com...615-30080.html

https://parts.belllexusnorthscottsda...615-30080.html

https://parts.prestigelexus.com/p/63...615-30080.html


I couldn't find the OEM PN for the pigtails, all that would come up was for the ES and RX350, so it'd be best to just call them for the part number you need according to your VIN.

Please keep us updated on your progress

 

122k and we replaced non-oem -- but mechanic offered to do oem if we need to swap out

 

Oops, meant to insert "word" above -- but that's great your mechanic offered to replace with OEM if needed.

Not sure how much your mechanic charges for the OEM part, so just offering a choice to get part for yourself and have your mechanic just charge you labor as both our mechanic and also our local dealership allows us to do so. That's why I have those "Go-to" websites I use and stock up on parts to bring and they just charge us labor.



* EDIT: Forgot to mention we also have a 2004 with 127k about to be 128k miles. We bought it last summer (July 22) at 124k miles, stored it over the late fall / winter months and just broke it out of jail a month or so ago.

 

If you also got after market wire harness, the chances are your mechanic had to splice the old end onto it. The aftermarket wiring harness that comes with the aftermarket knock sensor on ebay is not a direct fit.

There is a good chance the splice is the part giving you trouble.

https://www.ebay.com/itm/30421189766...3ABFBM0I7psNRm

 

I might be wrong. According to this old post, it is the sensor side that doesn't fit with the old harness
https://www.clublexus.com/forums/sc4...ustration.html