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Engine light on

1997 lexus ls400 204500 miles, engine light is on code P0340 (cam shaft position sensor bank 1), rough idle at start, once the car warms up it runs ok but loss of power, hesitates, if press more on gas pedal the car jerks. i have replaced both cam shaft position sensors and engine coolant temp sensor but no improvement. any ideas what could be the problem?

Check the wiring for the sensor in bank 1. A replacement sensor won’t fix things if it can’t get the signal to the computer.

I agree w/shadowfax, given that you have replaced the sensor already, this seems like an electrical connection problem. It could be a problem with the on-board computer too. This is usually diagnosed by replacing the computer assembly, and seeing if the problem is fixed. Finally, while unlikely, the sensors you replaced – while new – they may be faulty or may have been replaced incorrectly.

Use dielectric grease in the connections, too. This ensures moisture and water stay out of the connections. Obviously, moisture isn’t a good thing, and the connections will rust leading to more indicated failures, which will just be the wiring, leaving you right back where you are now.


i will reinspect the wires and connections. but i am sure it looked fine.

Looking fine and being fine are two completely different things.

it will also set this code if one of the cams is out of synch as in a timing belt that has jumped timing.

Be sure to ask you mechanic if this could be caused simply b/c the light is supposed to come on due to some service interval schedule. On some cars this light comes on not b/c of a problem, but at certain mileage intervals. From your description of the code read, this doesn’t sound like the cause, but these codes can be confusing. Your mechanic should verify you aren’t chasing wild geese.

It could be electrical or the timing belt, my mechanic did the timing belt at 175k and it was okay till recently 204000 I don’t wanna take it back there anymore he charged me $400 for replacing two camshaft sensors.

It’s always quite possible that the loss of power, hesitation, etc is not related to the cam sensors or cam sensor circuits at all.

This could be related to something that may not even set a code. (fuel pressure or volume, MAF sensor, air leak, weak compression on one or more cylinders, etc)
At 200k miles plus it’s anybody’s guess but I know the first thing I’d do in a shop setting; run a compression test. This will verify the engine top end mechanical condition and allow you to determine just how far to go, financially, with solving this problem.

Well the engine does have noise like tic tic tic tic while idling which doesn’t sound good. I unplugged the MAF sensor while idling the engine shut down, does that mean that the sensor is working?

here is a video of how it sounds

Did anyone try to even listen or watch the video above?

I did (and I’m sure many others did, too). You spent far too much time inside the car, and not near enough next to the running engine, for me to make a guess.

Then again, it’s a video. Without the proper tools to allow my ear to get into the various parts of the actual motor, it’s really hard to tell.

here is another video if it helps.

By “check the wire” I did not mean “Look at the wire and see if it’s there.” Checking the wire involves using a multimeter to be sure that 1) the wire isn’t broken internally somewhere and 2) the proper voltage (as specified in the shop electrical manual) is there.

If you don’t want to take it back to your mechanic, I sympathize, but unless you get under the hood and do the work yourself, you’re going to have to take it to some other mechanic to have it looked at.

All that being said, that engine does not sound healthy to me, though it’s difficult to diagnose exactly where the sound is coming from based on the sound from an on-camera mic that isn’t very high quality to begin with. Based on the sound, however, it is possible that engine damage is happening when you rev it like that, and so you need to weigh whether not taking it back to the mechanic is worth potentially destroying the engine.