How many ECM events/non-events to activate & deactivate CEL/MIL

[Chip]

Ive been exploring previous threads regarding diagnosis of the CEL/MIL coming on & I have read my FSM for the OBDII code P0401 that I am getting from a basic code reader/scanner. However, I am trying to understand the number of problem 'events' that causes the CEL to activate and the number of non-'events' that makes it deactivate.
With the weather getting warmer, it seems to come on mostly in the middle (heat) of the day and go off in the morning or evenings when it is cool... weather/temp related??
I am getting ready to begin the FSM procedures of elimination for the DI section on EGR insufficient flow. From previous threads, some of you out there seemed to have a better understanding of properly following the 'recommended' troubleshooting/solution procedures and I would appreciate feedback on what I have described above that would save me time...Bottom line, does what I describe have an obvious solution based on your experience(s)? or should I expect a 'goose chase' without specialty diagnostic tool(s)?

I rarely post because I can usually always find what I am seeking from previous threads on this Awesome forum! ...and I only have 2 yrs ownership experience.
Thanks ahead for any help.

'97 LX450...94k miles

 

[ParadiseCruiser]

Chip -

The P0401 MIL activates/deactivates on a 2-trip detection logic, roughly as follows...

1. Warm up at idle (accessories off)
2. Run eng at ~50 mph for 3~5 min,
3. Idle for ~2 min
4. Turn ignition off
5. Restart, and repeat #2-4

More completely described in the LC version of the FSM on pg EG-259; should also be in the LX manual if that's the one you have.

After all of the threads on this subject, it appears that any one of the components can be the source of trouble. In my personal experience - two complete rounds on this particular code - the culprit was the vacuum modulator both times. In any case, I do not believe there are going to be any shortcuts on this one: You really need to troubleshoot each component according to the book to find the trouble.

Cheers, R-

 

[Chip]

Thanx, I didnt expect many replies...but I am a logical thinking kinda guy and what you said is logical. Thanx for the reply. I'll get back to fundamentals...I guess if there was a shortcut, I would have found it in the various threads.

 

[Beowulf]

Chip,

Ron is right on target with his advice. There are 4 primary components in the EGR system plus some interconnecting hoses and some electrical wiring.
(In no particular order...)
* EGR valve
* EGR modulator
* VSV for EGR (vacuum switching valve)
* EGR temp sensor

The most common "failing" 80 components from what I've read over the past 5 years are the EGR modulator and the VSV for EGR. I cannot remember anyone reporting a confirmed failure of the EGR temp sensor.

Another common failure is the interconnecting hoses as they become clogged with carbon. There is also an EGR passage going through the intake assembly that has been the source of the P0401.

The FSM has a procedure for cleaning the EGR modulator filter. You can try it but it usually doesn't help and you will know immediately if cleaning is going to help. I believe it was Kirt that posted up a pic of his one time and it was clogged badly with carbon so cleaning helped his MIL.

Good Luck and keep us posted on your progress and what you finally decide is the problem.

-B-