Knock Sensor And Over Drive

[tong]

2000 Lexus RX300, about 110,000 miles. Like other member’s car, had a code P0171: bank 1 too lean- several months ago. Cleaning the mass air flow meter but no use. Then came the code P0325-knock sensor 1 Circuit malfunction (Bank 1). Did nothing about it because the car runs well. One day, suddenly, the car could not get into reverse and then could not go to over drive: when speed reaches 60miles, RPM is 4000-4500. Two local auto shops said it’s the transmission failure and it would cost about $3,000.00 to $4,000.00 to replace it.

Reading the posts from other members (really appreciate them and that inspired me to do the same): it looks like it’s a common problem for the Lexus (shame on Toyota to have so many troubles for Lexus) and it relates to the knock sensor. So I decided to try to replace the knock sensors first to see it works or not. And it really works.

Thanks for the information from other posts, I bought the parts from Conicelli Toyota dealer in Conshohocken Pennsylvania from their website partznet.com at much lower price with no sales tax, no shipping charge (over $250.00 order).

Knock sensor #89615-12090 $123.83 each

Plenum gasket #17176-62030 $10.33 (for upper intake manifold) from local Toyota dealer

Throttle body gasket 22271-0A020 $6.48 from local Toyota dealer

Lower intake manifold gasket –left #17177-20020 $22.73

Lower intake manifold gasket –right #17178-20020 $21.83

Knock sensor wire part #82219-07010 $22.14

By-pass hose #16261-20010 $9.11

Buy a Haynes manual “Toyota Highlander Lexus RX 300-330” from Kregan or Pepboy

At least having 10, 12, and 14 MM ratcheting ratchets, a hose clamp pliers and buy a socket cap tool #9 43303 from Sears. It’s about $10.00 and it makes to take off bolts on the back of the intake manifold possible and much easier.

It’s not an easy job so prepare at least for a 2 days at weekend to have a plenty of time and be very patient to do it.

Feeling the torque: I have a torque wrench but I had a bad experience to use it. So, when you loose the bolts or nuts, feeling how much strength you have to use. Then, try to use the same strength to install them.

First step: Take off parts on the outside of intake manifold

1. Remove wiper arm

2. Remove the plastic cowl cover and vent tray

3. Remove windshield wiper motor with electrical connector

It’s necessary to remove these parts to get access to remove intake manifold and they are easy to take

off. Just remember to put these parts on the order with all the bolts and nuts.

Second step: Remove vacuum control switch

1. Remove engine cover

2. Label each vacuum and coolant hose with tape and disconnect them

3. Remove the nuts and take off the vacuum control switch

At first, it looks like very complicated because so many hoses there but each one have a fixed length and

only suit one place, so, if you label them carefully, it’s not hard to put them back later.

3rd step: Take off upper intake manifold:

1. Drain the coolant

2. Disconnect ground strap from the left side of the manifold

3. Disconnect PVC hose from PVC

4. Loose 3 mounting bolts that connect intake manifold with throttle body

5. Take off 4 bolts on the back of the engine. 3 bolts are connected to the back of the manifold: one (14mm) is on the engine brace, one (10mm) is for ground and another (10mm) is for Power steering hose. The forth one (12mm) is to connect throttle body to the right engine hanger. When removing the forth bolt, you need to take off the heater hose first.

The most difficulty one is on the engine brace with intake manifold (14 mm). Because the brace has curve on sides and the space is so limited between firewall and the manifolds and is in the back, you have to put a cap (the tool bought from Sears) into a socket, and then use a ratcheting wretch to turn the cap to loose the bolt on the brace. You could not take the bolt out even after you totally loose it; you have to use a screw driver to pry the brace to get a sufficient space to take the bolt out. Other two bolts are easer than that one to take out.

6. Loose 2 nuts and 2 bolts on the upper intake manifold. When loose the bolts, try to feel the torque. The two bolts are very tights. I have to use a ½ inch size socket to loose them. Then, move the upper intake manifold.

4th step: Take off lower intake manifold

For the purpose of replace knock sensor, you don’t need to remove injectors and fuel rails from the lower

intake manifold. That’s a big relief.

1. Disconnect electrical connectors from fuel injectors and move heater hoses from lower intake manifold.

2. Remove 9 bolts and 2 nuts following a cross pattern sequence and take the lower intake manifold off and put it on the side. You need to remove air intake duct to make space for the lower intake manifold.

3. Remove a water transfer hose. You can see the 2 knock sensors now.

4. Disconnect the electrical connector for the knock sensors. It’s not very hard to push it off from the connector but it took me a long time to get it off from support connector that attached to the vehicle body. I had to break it off then use a plastic cable tie to tighten the new cord to the support connector. I thought this kind of connector is not for reusable.

5. Took off 2 bolts and 2 nuts, and then remove the water outlet which secures the left side of the gasket.

6. Use a 1 1/16 wrench or a flexible wrench to loose the knock sensors and replace them with new ones.

7. Replace the both gaskets and install the water outlet and lower intake manifold.

5th step: Install intake manifold

The hard part is to put the 4 bolts back into the back of the up intake manifold. From my experience, put

the power steering hose bolt first because the hose connector has to put into the curve of the manifold.

And don’t tighten any bolts until you put all bolts into the thread. With right tools and patient and care,

Most of us can do it.

After replaced the knock sensors, the car can go to over drive now. The code P0325 is gone. Based on

repair manual from Lexus, the relationship between knock sensor and over drive is: when no

knock sensor 1 signal to ECM with engine speed between 2,000 rpm and 5,600 rpm, and the ECM set the

corrective !Removed! angle value to the maximum value.

I think the knock sensors may be not bad at all but just the electric harness. Change both the knock

sensors are just for the safe purposes because as DIY mechanics we don’t have the device and the

experience to test it, and we don’t want to take the risk to take off the intake manifold again if changed

the harness did not resolve the problem.

This is just my experience and I just want to share them with my club members. Take cautious when you

work on your cars.

The code P0171 is still there, it may be something wrong with injector or the Max airflow meter or O2

sensor. Hope someone find a better way to fix this Lexus problem and post it here.

[mccldwll]

I read this post about knock sensors creating problems, and other posts about how it is unnecessary to use premium (91+) fuel since knock sensors correct for "ping", and can't help but wonder whether an over-reliance on the knock sensor to correct for octane leads to premature failure. I know I've heard something to this effect in the past. Any possibility this is the case? Also, I often hear that may get 1 to 2 mpg better with premium under certain conditions. That's 5-10% better mileage, and with gas at $3/gal, could easily be worth paying extra for premium.