djamps

Have you done a compression test?

DK Audio

Well, what do you know, my CEL came on this morning. Here are the codes, "P" means pending...

171
300 P
301 P
305 P
135 P

DK Audio

Any ideas? I have not done a compression test, don't have the equipment to.

DK Audio

On my way home from work my check VSC came on and check engine light flashed for a little bit. All the above codes are now not pending.

135
171
300
301
305

Gdwrench35

If, when the problem is not occurring, the engine runs normally, then your compression is ok. That problem would not come and go. The odds of you having a compression issue are slim to none unless you have a gillion miles on an engine you've abused.

From what I see of your codes, you likely have a bad A/F sensor. Bank 1 upstream. Disregard all of the codes except the P0135. You need to monitor the signals coming out of the sensor itself (data stream) on a scan tool and see if it is responding correctly. If you don't have this ability, simply unplug it and see how it runs without it. The damaged heater circuit is likely shorting out the ECM's ability to manipulate fuel mixture, causing your lean codes and misfires. Very common. Unplugging the sensor will force the car to run on a preset (rich) fuel mixture. If the car runs better this way, then replace the sensor. DO NOT drive the car very long with the sensor unplugged as running overly rich can cause catalyst damage and those suckers are expensive. Unless your good with a welder, then its a pretty cheap repair.

DK Audio

Thank you! The car has 150k well cared for miles so yeah, I doubt compression.
Do you know the location? I've tried searching without luck, bank one is driver side, right?

Gdwrench35

Left bank, or driver side. The upstream A/F sensor will be the one in front of the catalytic converter in the exhaust pipe. Follow the exhaust, starting at the driver side exhaust manifold down. The first sensor you come to is it. I'm not certain to its exact location but its usually right after the exhaust manifold. The connector itself may be in the engine bay or under the car. Find the sensor in the pipe, follow the wire to the connector, and unplug it.

Make sure you clear the codes after you unplug it. It will likely set a code right away for O2 open circuit and stay in open loop but thats ok for a short time to test it.

DK Audio

Great, thank you so much for your help. Is this an OEM only part or standard at an auto parts store? Not sure how much truth this has but I just read that Lexus doesn't actually manufacture these sensors, they buy them elsewhere.

Gdwrench35

I always recommend using dealer parts if you intend to keep the car and can afford the extra cost. Otherwise the parts store version will work just fine, just wont last as long. If you go that route, I'd recommend the Bosch brand or NGK. I also recommend replacing both upstream sensors at the same time to help keep the fuel trims balanced correctly.

And don't forget, as I've stated before, prove the part out before you buy anything. Try and watch the data stream and see the sensor fail. You can take Ohm readings from both sensors and compare the suspect sensor with a known good one. Unplugging the sensor should work to at least take away the lean miss so you can tell its causing it. You can also add some carb spray to the intake tube while the car is running and watch data to see if the sensors respond correctly.

Please understand, there could be a lot of different things causing your problem. You've got to isolate it down and prove it. Guessing can get expensive. I'm basing my 'guess' (which until you prove it, that's all it is) on your fresh set code list and the assumption that you installed your parts correctly. The misfire codes are expected with lean codes set so you can disregard those. The lean code just means a lean condition exists with no suggested cause. The A/F code tells me that either the ECM, A/F sensor, or the connection between the 2 are failing. If your ECM was failing, you'd have a lot more symptoms. The wiring between the 2 is unlikely but should not be overlooked. Always inspect the looms and connectors for damage or corrosion. And always put them back in their proper holders. They are in those things for a reason!! The sensor itself, which is exposed to extreme hot and cold temps with moisture and vibration and such, is the most likely culprit of the A/F code. The A/F code is the most likely cause of your described symptoms. But again, its still just a guess until you prove it. Things like the Air intake temp sensor, coolant temp sensor, bad gas, and so on, can cause symptoms like this as well. Either way, you've got to fix that A/F code before you go any further in the diagnostic.

DK Audio

Drivers side, unplugged the sensor (3 wires, black white and blue) before the cat, right after the tin heat shield. Cleared codes, drove the car, no change, still got misfire codes popping up, car still shakes at a stop. Not sure if I got the right sensor but I did not see one before it. I saw another after the cat which I assume is just O2.

djamps

If the sensor is bad and throwing heater codes I doubt the ECM is using it for closed loop corrections (plugged or unplugged) -- so it doesn't surprise me you didn't see any difference. your best bet is going to be swapping it out with a working unit.

DK Audio

So did I have the right sensor? On this diagram I don't even see it, I see "Heated Oxygen Sensor (Bank 1 Sensor 2). The one I unplugged was before the CAT so I think it would be called "Heated Oxygen Sensor (Bank 1 Sensor 1). Is that the correct part in question?

djamps

Sensor 1 is pre-cat and sensor 2 is post-cat (or even IN the cat on certain vehicles). Either way, #2 is further away from the engine than #1.

DK Audio

Right, this is the part in question though, right? What GDWrench calls upstream Bank 1 A/F? I'm wondering because Lexus calls it O2 sensor but GDWrench is questioning my A/F sensor. I just want to be sure I am looking at the correct sensor. It is pre cat on drivers side.

dicer

He means the O2 sensor. A/F ----- Air / Fuel, and the O2 sensor is what helps the ECU calculate the correct Air fuel ratio.
And like mentioned don't just replace the one side, do both of them. Get them from Rock auto, just a more affordable price. Then you can get the 2 for much less than one at the dealer.
Pre Cat means before the catalytic converter, and is in the exhaust manifold just above the bolt flange where the exhaust manifold and cat connect.