GB42

My 1999 LS400 with 150k has had both post cat sensors fail. Replaced the passenger side no problem with direct connect sensor. Problem with replacing drivers side one. In removing the carpeting, I cannot remove carpeting around/at the gas pedal. The gas pedal needs to be removed. How do you remove the gas pedal, it seems to be a double ball and socket at the base and I cannot pull it out/off. HELP anyone?

Pensioner2

My car is an 1998 LS 400 with 275K miles on it. Twice in a month the check engine light came on. OBD2 scan showed O2 sensor upper, bank 1. My freeway fuel consumption dropped from 29 to 22 at 70mph on a long journey.

So, an O2 sensor was dying. There are two on each bank. I decided to change all four.

I bought Denso OEM sensors. There are Denso universal heated O2 sensors available for half the price but they are wire ended and you have to cut off and re-use your plugs. Splicing, soldering and satisfactorily insulating the wires in the hostile enviorment around the catalytic convertors did not seem to be a good idea. I bought the OEM specification sensors.

I drove my car up my ramps and slid under it on the trolly. I removed the splash guard and surveyed the job. It looked daunting from the access point of view and I almost decided to give up and go to my local mechanic cap in hand, but I decided to procees at least with the bank 1 upper sensor. I unplugged the lead and threaded a 22mm combination ring spanner onto the nut expecting it to be seized and tight. It loosened a flat easily and I was able to remove the sensor turning it with my fingers while twisting the cable to reduce the required torque. The sensor threaded body and the thresded socket in the exhaust pipe were both stainless steel. I believe the sensor was easy to remove because it had a compression sealing washer similar to washers on spark plugs. I applied a little of the copper anti sieze grease supplied with the sensor to the threads and screwed it back in, nipped it up and pluged it in.

I then started the car and it ran smoothly. Empowered with my success I followed the same procedure and changed bank 2 sensor 1 as well.

Started the car and it ran smoothly.

On to the sensors number 2.
They are screwed into the side of the exhaust pipe after the catalytic convertors but the wires go through the floor of the car in grommets. Looking at the service manual for changing them I realized that the diagram with the sill scratch plate, the carpet, the throttle pedal and the tube bringing hot air to the rear passengers was conveying something. The diagram was conveying that these parts needed to be removed to access the sensor grommet. The sensor plugs and sockets are mounted on either side of the transmission hump at about calf height below the carpet. The floor grommets are below the heater hot air tubes which run under the carpet to bring hot air to the rear passangers' feet.
I removed the sill scratch plate and the four bolts holding the drivers seat to the floor. I laid the seat back onto the rear seat to give free access to the front carpet. I lifted the front carpet from the sill and was able to feel the heater tube and the 10mm bolt securing it to the floor. I removed the bolt and was able to pull the heater tube from the coupling in the heater box and I used a 6" length of 2"x4" to hold the heater tube and carpet up to be able to release the wire grommet into the car. The carpet can be slipped down from the gear shift consol to access the plug and socket clipped to the tx tunnel. I removed the plug for the old sensor, plugged in the new one and then fed the sensor and 12" of wire through the hole in the floor. I inserted the grommet into the floor, Screwed the greased threads of the sensor into the exhaust pipe and repeated the process on the passanger side. There is a A/C water drain pipe under the carpet running from the heater box to the floor near to the sensor socket. If you knock it off as I did remember to push it back on other wise you might get a wet carpet next summer.

I disconnected the battery for 10 minutes. I believe this causes the ECU to dump its stored data and reacquire is when the motor restarts.

It was all a lot easier than it sounds when reading the procedure, really.

I am now back to 29mpg on the freeway if I take my time. This inspired me to change my plugs and the ECU temperature sensor (bank 2 between cylinder 2 and the thermostat cover). My sensor checked out fine in boiling and iced water but I changed it anyway. This sensor I bought from Lexus. The generic ones are not supposed to be as close tolerance as OEM specifications. The Lexus sensor had three keyways on the outside to restrict which plug will be able to connect. The generic sensors have no keys and any old plug can connect to them unimpeded. I make this comment beacuse I initally went to Toyota and bought a simlar sensor for the same application. It was cheaper but the key positions were different and the Lexus connector would not fit. I did not bother to check and compare the resistance of both in iced and boiling water. I just learned a little lesson and bought the Lexus sensor which was only $5 more.

Nothing else to report except job done and I have placed an OBD2 scanner box on my Xmas list. I have lasted 15 years without one but now I learner another little lesson there too.

Now my question.
Does anyone know what the exact purpose is of the diagnostic data socket on top of the motor? What data can Lexus monitor through it and should I add that box to my Xmas list too?