Recent purchase of a used 2000 RX300 with 96K miles. Previous owner had just replaced both knock sensors/harness with parts obtained from Amazon. Will be asking what code it was throwing before the work and if the old knock sensors were tested along with a list of what parts were replaced and what manufacturer. Previous owner also stated the car sat for many many months and it had 1/4 tank of fuel.

ON the drive home CEL came on with a 171, 325 and 330. Yay!

Removed and cleaned MAF. First time did not work so swapped with one from my 2002 Camry, (looked the same and googeling around looked like even thought numbers were different it should work), Did not fix the 171, (kinda odd because never had that error on the Camry after over 50K miles...). So switched MAF's back but looked very carefully at the one originally from the RX before re-installing it using a flashlight and magnifying glass, (it difficult for me to see much without out the magnifying glass ha ha. Noticed a very slight off color on one of the internal sensor wires. So spent another 5 minutes carefully cleaning with MAF Sensor cleaner then let dry and reinstall.

Now the 171 is gone but now getting 325/330, (usually on freeway between 2K -3k RPM). Under over does not seem to throw code. Also getting the OverDrive disable/limp mode if not in Overdrive when the code throws.

After reading many threads I am curious how often the codes are thrown with no other code for a real condition such as misfire and what else can cause the sensors to report a real condition yet throw no other codes? For example what if a very small amount of coolant is getting into a combustion chamber but not showing bubbles at the radiator cap or throwing a code - can this cause the knock sensors to report a condition? I have been re-setting the code while driving with a handheld scanner so I can still drive on freeway without over revving by not using overdrive. I will leave the code and continue to drive to see if any other code appear.

We also have been using 91 Octane and several bottles of fuel injection cleaner with (PEA). Read several threads suggesting Knock sensor codes may be related to bad/old fuel.

Next step may be to do the Knock sensor hack, adding a 3rd sensor and tying it to both leads and trick the ECU. Concern is if we have a legitimate condition and the 3 knock sensor will not do much to report future legitimate conditions. This is for testing purposes only.

Thanks in advance for any suggestions.

 

Hello,

The codes you have are pretty self-explanatory, especially if you looked through other forum threads on the subject.

Knock Sensors are an essential piece of any Fuel Injected vehicle, as Knocking, or Detonation, can wreck an engine in seconds, even if you run Premium gas. This is precisely why the Limp Mode for those codes is so restrictive, ensuring that there is no chance of your engine running into knock, and that you as an owner won't have a chance to miss it, like a stick shaker in modern aircraft, by resetting those codes each time, you are not helping anyone.

There may be a chance it's as simple as the Wiring Harness under the Intake Manifold, but more often than not, it's the sensors themselves, or a combination of both that fails. Considering the amount of work to access those, it usually makes more sense to replace everything at once, unless you want to dig in again later at some point.

There is a very good reason why those sensors are where they are, if there was a chance of placing them elsewhere with the same result, trust me, they would have done it. All the ways of bypassing or otherwise altering this system are mostly half measures that are mostly there to get rid of the light on the dash, they are not there for a solid permanent fix. If that's something you are after, not sure what to tell..

Other thing is P0171 code that you had, it is very likely related to the Knock Sensor issue, as Knock Sensor Codes set the Ignition Timing dead at 0 to prevent any chance of knocking, which could result in a Lean Condition. MAF sensors are very fragile, especially if you go straight for the measuring wire, by this very intense cleaning, there is a possibility that you skewed the readings of the sensors enough to get the code out of the system, but it doesn't mean that it won't come back once the Knock Sensor issue is resolved, not that the sensor may not be supplying correct information. What's even worse is that you may not even end up getting a code again, just because the readings will be just within the tolerance window, but the engine won't run right, increasing wear and fuel consumption.

In short, my suggestion would be to fix the issue correctly and never come back to it, rather than trying to find workarounds that may come haunting you later.

Hope this helps and best of luck!
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Hi,

Thank you for the input. l read several posts about getting bad sensors after a lengthy install procedure. Understood there are counterfeit sensors and cheaply made ones that should be avoided. I was able to find out from previous owner that he had paid a mechanic 400.00 to install 2 cheap sensors and a cheap harness, hopefully these cheap sensors failing is the issue. I will be "temporary" running this hack to rule out any issues upstream from the sensors/sensor harness/plug before doing the bigger job to install Denso sensors.

Is there a condition with a MAF sensor that was cleaned and no longer throwing an error whereby it can cause harm without throwing an error?

Thank You.

 

ECU is a powerful system, but it is not all-encompassing, it can only judge things with the information that it gets from the sensors, it cannot look inside the engine to see how the combustion is doing, per say. That is to say that if the readings did get skewed during the cleaning, the ECU will make a correction for those readings regardless of how true they are, as there is no way for it to know any better.

To get into some more details, you can look up Closed Loop Control, where all the decisions are based on the Closed Loop of sensors, one backing the other, which creates a very precise, and most importantly, factual control system, it doesn't rely on a list of some predefined conditions. This system can be capable of diagnosing and excluding faulty sensors, but only if there are backups for them, which this car is not equipped with, so there is a chance that a faulty MAF sensor will not get you any codes, unless the readouts are so warped that the Fuel Trims are completely off the chart. That's probably why you got a Lean Code in the first place.

I've had a similar issue with my 2000 ES300, where the engine would noticeably stutter at every cold start, but would feel just fine otherwise. I first suspected a leaking Injector, as it would only happen after the car would sit for a while, but then looked at Engine Live Data and realized that a MAF sensor would be all over the place, showing different readings at every stop, with the engine being under the same conditions. The fuel Trims were off, the car felt strange, but still no light on the dash.

Hope this helps and best of luck!

 

Thanks for the replies. We are losing a very small amount of coolant with no external signs as of yet. My concern is prior owner replaced the knock sensors due to a real condition causing a code such as coolant in combustion chamber. For now I went with Beck Arnley, (I know its better to go with Denso - this is temporary until we fully diagnose the coolant loss). I installed the 2 knock sensors on the plate on the drivers side of valve cover. One interesting thing. Depending on which wire I attach to which sensor it will throw a 330 code but then when I switch the wires no codes at all. Does the ECU sync with one sensor then later if switched it detects that then throws an error? I noticed one sensor has a green dot. I also pulled the radiator side plugs to inspect to see any signs of coolant in combustion chamber., (picture attached), and debating weather to properly install Denso or Beck Arnley sensors. Its a very tiny amount of coolant loss.

Side note. Took in to local tire shop to get some new rear tires. They used floor jacks with no dish/adapter and bent the jack points. I have never seen jack points bend like that. I guess its hard to get good help these days.....

Thanks for the replies.

 

The sensors have two separate signals to the ECU. The diagnostic even says swap the connections to see if the problem moves.
If the problem moves it's the sensor. If it doesn't it's the wiring. No mention of "if it goes away".

Any chance these wire are spliced at the ECU? That might explain it.
https://www.clublexus.com/forums/rx-...ck-repair.html

Check the front of the engine by the oil filter. I've had a very slow coolant leak there for years https://www.clublexus.com/forums/rx-...l#post10932797

 

Yes the error goes away - depending on which wire is to which sensor there are not codes! With the 330 it was also disabling the overdrive. It was perviously spliced with the old , (cheap harness from Amazon previous owner had installed" to one of the new Beck Arnley sensors, (sorry I left that out - devil in the details). The latest code was with the new Beck Arnley Sensors/harness attached to right valve cover side plate hack which went away after switching the wires.

I will check the ECU. But if it were hacked I would think the error would reappear. No codes at all at this point with carful minimal driving. Previously the code would apprear after a mile or 2...

Thank You