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-   -   "Check Engine" light also indicates ECU "relearning" ? (https://www.team-bhp.com/forum/technical-stuff/105828-check-engine-light-also-indicates-ecu-relearning.html)

While reading the thread on an issue with a Scorpio in Ladakh (http://www.team-bhp.com/forum/techni...stuck-leh.html), I came across the information:

"The engine check light does come on at high altitudes and apparently allows the ECM to 'relearn' the oxygen levels being read by the oxygen sensor and change fuelling accordingly."

I went over the owner manuals of my Hyundai Tucson and Skoda Laura, but could not find this information in there. May be I overlooked, so will check again tonight.

So far, I thought that "Check engine" light means something is wrong and I should pull over and stop at a safe place to investigate further. If the same light, in certain situations, indicates that "engine is relearning, don't worry, please continue driving", what's the way to differentiate between the two?

There is no such differentiation, Check engine comes only as a warning or malfunction not learning.

^ +1. Altitude 'relearning' is always 'silent' - there is no indication associated with it. Error / fault annunciation in automobiles (like Check Engine light) are never ambiguously associated with *any* non-error operating situations as a policy by ALL ECU makers. The only exception is 'steady' light at start-up indicating 'busy with initialization', but then start-up is not a normal operating state.

I saw that discussion on the other thread :)

Few notes from the OM of Ford Endeavour (3.0l 4x4): Rev limit is restricted (limit not specified) at high altitudes ~ 16000 ft. This is by design and is indicated by the engine light switching and remaining ON, till when the altitude decreases. No special service is recommended in such circumstances.

So I guess it's something already LEARNT and designed :D

I'll however be curious to know what other owners report and if there are some cars designed to learn. Also, isn't the ECU operating on firmware which can only be updated by the OEM? Or is there a concept of ECU learning and writing into some memory or updating itself somehow?

More questions...

What happens when an OBD-II scan shows P1000 as the error code?

What happens when the engine is running rich due to low oxygen availability?

Why does the Scorpio come with two 'check engine' lights - one called the 'engine check/malfunction lamp' (#16) and the other called 'OBD lamp/transmission check/malfunction lamp'? How is an engine check lamp different from an OBD lamp?

If something is really wrong, ECU will put engine in limp home mode. So you will not be able to cross 1200rpm.
If your vehicle is functioning normally, you can keep driving till you get help. Sometimes bad fuel can get you this "non limp home mode" check engine light.

Different manufaturers implement error codes in different ways.
Some error codes are "error" situations. For example engine temperature sensor saying that coolant temp is high. It will put your engine in limp home mode.
Other error codes, for example in the safari "Rail pressure sensor error" just flag the check engine light, without any performance change.

that said, high altitude learning is always silent in the safari. Maybe scorpio is different. It all varies from mfr to mfr.

Without knowing the error code (scanning the engine), there is no way of knowing error code.

That's my understanding too - at least for my cars. But I am ready to learn :).

I would think so. If there is only one "check engine light" then it should be honored without ambiguity.

Ok, this is good information.
And did you come to know about this from the owner manual?

My point is, if the owner manual does not mention this, how would the owner/driver know of this (i.e. when to respect the check engine light and pull over and when to ignore it and drive on?).

Oh, OK, so Scorpio comes with two lamps.
So which one is supposed to be ON while the ECU is learning at high altitude? And what does the owner manual say about the two lamps?

Ok, but if this is the standard operating procedure, then should it not be mentioned in the owner's manual? Am I wrong in expecting this?

I mean if I get stuck like this in Leh, I should definately know when to fear the check engine lamp and when to ignore it.

What will happen if I do not choose wisely or apply one car's knowledge to another which works differently?

And yes, I surely appreciate that pulling over and calling for help may not work in Leh, but then that only highlights the importance of knowing "for sure" how the car works. Isn't it?

Yup, it is from the owner's manual (mine!). It is presented as a "note" and not under the "warning" or "caution" heading. To reproduce exact words: "Engine performance (rev limit) restricted above ~16000 ft altitude due to design intended protection. This would be indicated with engine light ON in the instrument cluster and should be restored to normal operations, once vehicle is operated below 16000 feet. No Special service is recommended in such circumstances."

Also, if I hadn't read this before and the engine light glows, I would have pulled over to the side too.

One question I have, though might be specific to the Endeavour, is whether by "rev. limit" they mean limp home speed? I tend to believe not, unless some owner here who has driven at this high altitude reports otherwise.

Awesome. Good Ford :).
Thank you.

Absolutely. That's the point.

So if I understand correctly, "check engine" light would mean limp mode above 16000 ft. Below that altitude, it will mean what it's name says - "check engine" (serious trouble).

Am I correct?

Does Endeavour come with on-board altimeter so that the driver can interprete the "check engine" lamp in the right context and take appropriate action?

Cheers!

Yes, if its written in your manual. Since each ECU is like a customized software, designed for that vehicle with standard OBDII codes (if they follow it).

One's note does not mean its applicable for all.

The vehicle doesn't have an altimeter. What I can think of is to get to know the altitude of the hills I'm visiting and "ignore, but observe caution" when the warning light comes on while I'm there. But this wouldn't be a very comfortable feeling as I can never get to know if something else has wrong.

Hi,
Great information! Highlights the fact that when it comes to software, what is absolutely obvious to one person (programming team) might be totally irrational to another. As such without knowing exactly what is done, one can only speculate. Because it does not have to follow 'our' rational thinking.

Regards
Sutripta

Right.

And are there different modes of this light? OFF, steady ON, slow blink, fast blink. At least that can help to demultiplex the signal.

That's a nuisance code mostly with Ford vehicles. Can be one of many things:
- Incomplete hard-reset cycle
- Some internal diagnostic test didn't complete on time etc.

Different in petrol and diesel. In petrol engines with ECU, the ECU will try to correct when Lambda sensor complains. In diesel it will show up in smoke till the ECU corrects itself (difficult to predict / comment, since there is an interplay of a few indirect factors till ECU figures this out). This is a rare condition in lower altitudes. Usually the atmospheric pressure compensation correction kicks in and corrects in a short time (50-200 secs, incl. sensing altitude change).

Engine lamp shows operation related errors inferred by ECU. OBD lamp (most likely, not sure) shows OBD communication related errors. Who knows, perhaps the MM guys might have faced too many bothersome unexplained intermittent problems on their test bench, and thought best to provide a separate lamp for OBD problems. :p

Is this picture is from the Scorpio owner's manual?

And the manual only mentions the name of the lamp and no description of what it means?

If you want someone to predict by the name, then one lamp says "check engine", while the other says "check transmission" (or OBD scan in progress)?

May be.

In any case, they have a dedicated lamp for "check engine" and another one for OBD related stuff (errors, scanning in progress, ECU relearning, etc?) and transmission malfunction.

So it appears that 4x4 and transmissions issues can be clearly identified from engine related issues, which is good.