INTERMITTENT ASR LIGHT AND LIMP MODE

[r44raven]

My indi is trying to track down a very intermittent problem, where the ASR light will randomly illuminate, and the engine drops into limp mode. Turning the engine off/on cures the problem - until the next time, which could be almost immediate, or 12 months away!

Fault reading indicates a problem with the front driver's side ABS sensor - but at the same time, we're getting ABS Code 30.

My questions are:-

Does an ABS sensor fault trigger Code 30?
Does an ABS sensor fault trigger limp home mode?
Is the Code 30 a ghost code, which then triggers limp home mode, or does the limp home mode trigger the Code 30?
If the Code 30 is real, what am I looking for?

Over the years, all the usual suspects, i.e. wiring harnesses, late date ETA etc. etc., have been renewed.

Any suggestions would be gratefully received.

 

[gsxr]

Limp mode triggers ASR code #30, which is a generic ghost code that can be ignored. It is a red herring.

Are you also getting ASR code #2 or #25 for left front VSS (L6/1), driver side ABS / wheel speed sensor?

Look at the E-GAS/EFP module faults, this will tell you what is causing the limp mode.

 

[r44raven]

Thanks for that, gsxr!

I've sent your reply to my indi for his comments!

Interestingly, I do have a brand new E-GAS module I could try for grins?

 

[r44raven]

Limp mode triggers ASR code #30, which is a generic ghost code that can be ignored. It is a red herring.

Are you also getting ASR code #2 or #25 for left front VSS (L6/1), driver side ABS / wheel speed sensor?

Look at the E-GAS/EFP module faults, this will tell you what is causing the limp mode.

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Sorry, should have asked before!

As I understand it, the front ABS sensor fault would not have triggered the limp mode?

And also, did the limp mode trigger the ASR light, or did the ghost Code 30 trigger that?

Thanks in advance.

 

[gsxr]

Correct - an ABS sensor fault should not have triggered limp mode.

The limp mode triggers both the ASR light and also the ghost code #30.

Limp mode is due to a throttle control fault of some sort, completely separate from traction systems. I assume that because there is no ETA / EFP fault light on the dash, MB decided to have limp mode trigger the ASR light instead? The new E-GAS module likely won't cure the problem. Pull codes and see what shows up. You may need to clear codes and drive it until limp mode occurs again, if there are multiple faults.

 

[r44raven]

Thanks for that! It's really helpful. I'll keep you updated.

 

[jaymanek]

I would follow gsxr advice and look for codes in other modules first... but when i had a similar issue and codes were sending me around in circles, it ended up being the transmission loom. I guess some kind of short, although i never actually found a physical issue with the wires...

took me 2 years to find and in the end it became an educated parts swapping exercise until the issue was cured. Hope its more simple for you!

 

[tanger]

OMG this was what my indy just spent the last year+ hunting down! Took apart the wiring harness, replaced the ETA, the ASR module, and the Air Mass Flow sensor. It turned out that the renewed ETA was NOT completely fixed. Put in another rebuilt one (from someone in FL?) and it fixed the issue. The rebuilder of the original ETA swore it was fine but it was not. I can't remember where the first rebuilt ETA was from, but maybe your indy should call Gary or Ed at Johnson Motorcars in Orange County, CA. They were the ones working on it.

 

[r44raven]

Thanks everyone for your additional input; as jaymamek suggests i'm going to follow gsxr's advice and look to the e-gas module for any fault codes.

Although what I am experiencing is annoying, I am not too despondent because searching this forum, there seems to be a large number of members here who have chased similar symptoms over the years - with many and varied causes eventually uncovered!

Hopefully, i'll get to the bottom of this one, and then be able to post a good result here!

 

[e500.org]

I had this - it really triggered when I activated cruise control. It was the E GAS module - replaced with a used one and did not have issues since.

 

[r44raven]

Limp mode is due to a throttle control fault of some sort, completely separate from traction systems.

I have a supplementary follow-up question. If limp mode is related to a throttle control fault of some kind - rather than the traction system - how is it that, in my experience at least, fitting non-matching rolling circumference tyres to the front and rear of the car will trigger the ASR light and limp mode?

 

[R129 UK]

I have a supplementary follow-up question. If limp mode is related to a throttle control fault of some kind - rather than the traction system - how is it that, in my experience at least, fitting non-matching rolling circumference tyres to the front and rear of the car will trigger the ASR light and limp mode?

I believe the wheel sensors have an input so different size tyres can potentially cause issues.

I have no idea how "sensitive" it is to deviations, my ML uses the same method for tyre pressure monitoring and it is rubbish, my partner has a Honda with TMPS which is insanely sensitive.

 

[r44raven]

I am aware that different tyre sizes can cause issues; my question is that if limp mode is not related to traction issues (one assumes here this means slipping/locking wheels, or inconsistent wheels speeds across the car), why is it that different rolling circumference tyres between the front and rear triggers limp mode and the ASR light?

My reason for asking is that I did get repeated triggering of limp mode when I had unwittingly fitted non-matching tyres front/rear - so I assume one caused the other?

 

[gsxr]

Limp mode can be triggered by several different faults.

I can't recall if different tire circumference can trigger limp mode. I know that a tire circumference discrepancy will cause cruise control to not work above a certain speed, and that if the rear tires are smaller, it can trigger ASR to engage under hard acceleration even when there is no wheelspin. But, in both cases, limp mode does not occur (at least in my experience, on my cars).

On your car, when you put the correct / matching tyres on, did your issue with limp mode go away with no other changes? Any chance you checked the fault codes stored when this happened?

 

[R129 UK]

Limp mode can be triggered by several different faults.

What is being described as limp mode here?

Is it activation of ASR and/or something else?

 

[gsxr]

Limp mode is where the ABS+ASR fault lights come on (at least, IIRC both illuminate) AND ALSO, the throttle pedal becomes unresponsive. Meaning, the throttle plate does not begin to open until the pedal is pressed halfway to the floor, and at full throttle, the ETA butterfly is only half open. It's also known as "emergency operation mode" or something like that.

Normally, the ASR ETA is fully throttle by wire. The mechanical linkage is a backup if the electronics fail (or, if faults occur which cause the computers to trigger limp mode). But the mechanical linkage has the limitations described above.

ASR should only activate when wheelspin is detected.

 

[r44raven]

On your car, when you put the correct / matching tyres on, did your issue with limp mode go away with no other changes? Any chance you checked the fault codes stored when this happened?

Yes, when I fitted matching tyres all round, I did not get any repeat of the limp home mode. However, that might have just have been coincidence - limp home happens so randomly and usually infrequently that there might have been no connection with me changing the tyres (and no, I did not get the opportunity to pull any codes).

This all occurred some years ago - and it is only more recently that limp home is recurring again.

 

[r44raven]

Limp mode is where the ABS+ASR fault lights come on (at least, IIRC both illuminate) AND ALSO, the throttle pedal becomes unresponsive. Meaning, the throttle plate does not begin to open until the pedal is pressed halfway to the floor, and at full throttle, the ETA butterfly is only half open. It's also known as "emergency operation mode" or something like that.

Normally, the ASR ETA is fully throttle by wire. The mechanical linkage is a backup if the electronics fail (or, if faults occur which cause the computers to trigger limp mode). But the mechanical linkage has the limitations described above.

ASR should only activate when wheelspin is detected.

The limp home mode I am experiencing is exactly as described by you, except that only the ASR light illuminates, not the ABS. Does this give any clue to what might be going on?

 

[gsxr]

OK - this may be normal, with only the ASR light on. Now that I think about it, yes, limp mode should ONLY turn on the ASR light, as the ABS system should still be active (it is completely separate).

I was thinking of ABS+ASR lights on with an ASR defeat switch - totally different scenaerio. My bad - sorry for the confusion!