Hey all, I have a 1996 LS400. When I got it; it had a code for the cam position sensor…P0340 I think. I bought two new ones, went to auto parts store, had code cleared and went on with my day. By that afternoon; the light was back on again with the flashing TRAC light. I went back to the auto parts store, had it read and the same code came up. I did some reading online and people were saying that the crank position sensor could also be bad. So, I drove two hours to the nearest store that had one, bought it, replaced it, light went off after battery unhook and re-hook, but it came back on yet again!!! There is a crack in the EGR pipe, but I don’t have any way to pull the code until I get to a store again. Any light shed on this would be appreciated. Thank you!!

 

Well, first, you need a ELM327 code scanner. They're like 20 bucks and way cheaper than going through the hassle of driving 2 hours to a shop to use theirs. We don't know if the current light is the same code as before, or, something new, or, if the sensors were installed incorrectly, or, if there are multiple codes.

Leaky EGR doesn't necessarily mean the car will throw a code. Any other issues? Drivability issues?

Also, the obligatory: Has the ECU been repaired?

https://www.clublexus.com/forums/ls-...capacitor.html

 

Thank you for the reply. The car drives really well. No hesitation, stutter, etc. Starts just fine each and every time I need it too. When I had the initial codes cleared the first time; Two new codes under the “catalyst” sector popped up. I had those cleared and they haven’t cane back Since…or so I thought. This new light could be them. As far as the installation; I’m almost certain I did them correctly. Just to clarify; when talking about engine banks; the last bank is determined from sitting in the drivers seat correct? That’s what I’ve always been told.

 

Your type of problem often needs to use an oscilloscope to troubleshoot. As long as cam sensors are OK, your symptom means that the ECU is detecting some abnormality or the ECU is running with too much ripples. I'd simply check waveforms of 3 sensors as are like the chart below. NE means the signal from the crank position sensor and G1/G2 from cam position sensors. The relationship of these 3 signals should be like this below sharp and there should be no strange noises. If the phases are not like this, it means that the timing belt is skipped. If there are noises, it probably is caused by the too much ripples and you need to check the ripple level as is explained at the FAQ page.

 

Thank you! I will look into that. The car is a replacement for my old daily driver. I paid 2k for it and it looks halfway decent runs good, etc. The CEL is just bugging me kinda lol.

 

So I went today and bought my own OBD tool. The CEL came back on and was still pulling P0340. I cleared it shut the car off, restarted it and it came back on. All parts are new. Both cam sensors and crank sensor. Could this be a faulty part? The car still runs perfect with this light on. Should I not worry about it??? Thank you to all in advance!!

 

You can drive it with the CEL on. It's just that the ECU is now running in what most call "limp" mode - the ECU just uses a predetermined set of parameters that allows the engine to run.

You replaced just the one sensor?

Try swapping the new sensor A with the existing sensor B. See of you now get a Bank B circuit malfunction (P0390 - the DTC follows the sensor).

• No - the problem most likely not the sensor but the A circuit for that sensor. You need to do what Yamae suggested in post #4. There's also a link in that post for checking ripple voltage without removing the ECU.
• Yes - the sensor is faulty.

 

I have replaced both sensors as well as crank position sensor.

 

If I may, let me rephrase what Yamae and Paulo are saying. The tests they have suggested will determine whether the sensors have failed, or, if it's the ECU that's reading the sensors incorrectly.

What Yamae is suggesting is measuring the sensors directly to determine if it's instrumentation failure. Paulo's method of swapping the sensors is also a test to determine instrumentation failure, and is more friendly to those of us without advanced tools.

You've already replaced the sensors, so they will probably pass these tests. But, still best to do it just to be safe. If they pass, the next most likely item is the ECU.

The thread Yamae linked to:
https://www.clublexus.com/forums/ls-...-by-yamae.html

is how you can test to measure the health of your ECU.

Side note - ECU failure is inevitable. It's not an "if", but a "when". This is why I asked had your ECU been repaired.

 

You once wrote,"I will look into that".

I still don't hear any results of it. Instead I found you started another thread and barking the same thing. I must say that you are in a closed loop where you are trapped in. Sorry to say that your way of troubleshooting is not quite effective. You probably can't escape from it.

A computer controlled car needs to use electronics tools such as a code reader, a DVM and an oscilloscope for a quick troubleshooting. If none, it requires you time and money throwing parts next to next. Why don't you measure the ripple at least. It only requires a DVM and a capacitor which cuts the DC component.