W211 Engine Warning Light - Limp mode

[Crazy Mike]

My 2002 E220 cdi has an intermittent fault where the engine management warning light comes on and the car goes into reduced revs / power / limp mode. This has happened 3 times in the last few weeks and after stopping, switching off and leaving the car for a while, it starts and runs with no problems showing. The last period between warning lights coming on was 1.5 weeks (c 200 miles). There's no other noticeable problems apart from these 3 observations.
1) The cooling temperature gauge barely reaches 50 - 60 deg (This may have been like this for a while so may be totally unrelated)
2) After a run, there is a 'rattley' type sound from underneath the car when stationary. Nudging the exhaust with a stick seems to temporarily cure it. This again may have been happening for some time. Not sure.
3) I always re-fuel at Tesco but last tank, 250 miles ago, was from a independent BP garage. May just be coincidence though.

Whilst the warning light was on with engine running, I used a Launch Creader CRP123 diagnostics and although when trying to read one of the Engine modules, it reports a communication error, the only other significant fault is C25D8 'Inspect wheel Brakes for mechanical faults'. There are a couple of other fault codes that cannot be found in the database, 1234-0000 and 1222-0000 so I don't know what these could be.

The advice is likely to be to find a Indie with Star diagnostics or take it to main MB dealer. Does anyone know a Indie with Star in the Oxfordshire area ?

Any thoughts or recommendation where a Indie with Star lurks - would be very welcome !
Thanks

 

[mercmancdi]

If your running as cool as that all the time ,, should I think be around 88 -90 so that’s not good as some sensors are temperature related if I were you I would take cheap option and get a stat put in and take it from there.

 

[W1ghty]

Ian at Star Services , Caversham near Reading any good for you ?

 

[AP211]

+1 on starting out with the thermostat replacement.

You should be running at either 87 or 92 degrees depending on the thermostat (factory stat is 87). It might not be the cause of all of your issues but it's one issue and a good starting point.

 

[Crazy Mike]

Thanks for the replies.
I'll start off as suggested with a replacement thermostat. If that doesn't fix it then at least the engine gets it's coolant replaced which probably needs doing anyway.
Star service at Caversham noted - thanks
Will post an update in due course. Thanks again.

 

[Crazy Mike]

I have now changed the thermostat and replaced the coolant which has fixed my low temperature reading - back to the 90 deg mark now.
However, the engine management light still comes on and goes into limp mode. I managed to have a diagnostic check using a Snap-On device which reports that the accelerator pedal potentiometers are at fault here. The guy who did this seemed fairly certain that this was the only fault so it's highly probable that this is causing the issue.

So my question is does anyone have experience of Snap-On diagnostic equipment (I guess like others there are many models) and their diagnostic accuracy and does anyone have any knowledge of the accelerator pedal on the early W211's needing replacement. It's pricey replacement from MB and I can't see a aftermarket option.

It seems there is a lack of Indies with Star diagnostics in my area. Any thoughts anyone ? Thanks

 

[W1ghty]

I have now changed the thermostat and replaced the coolant which has fixed my low temperature reading - back to the 90 deg mark now.
However, the engine management light still comes on and goes into limp mode. I managed to have a diagnostic check using a Snap-On device which reports that the accelerator pedal potentiometers are at fault here. The guy who did this seemed fairly certain that this was the only fault so it's highly probable that this is causing the issue.

So my question is does anyone have experience of Snap-On diagnostic equipment (I guess like others there are many models) and their diagnostic accuracy and does anyone have any knowledge of the accelerator pedal on the early W211's needing replacement. It's pricey replacement from MB and I can't see a aftermarket option.

It seems there is a lack of Indies with Star diagnostics in my area. Any thoughts anyone ? Thanks

If it were me , I would find out the cost of the part you think is at fault (from MB) . If it wasn’t expensive I would get your garage to fit it and see if that sorted it .
If the part is expensive I would travel to an Indy with Star before throwing parts at it .
If you have breakdown cover what about calling them out for a diagnostics check ?

 

[Supernoodle]

What exactly were the faults though? Did your guy with the Snap On tell you exactly what was reported? The wording is important. There are multiple pedal faults that could flag, circuit high/low, range/performance, etc. One track or both tracks?
Understanding that should help guide what possible reasons could be.

They're normally easy to check.
Most tend to use two analog tracks, where the signals oppose each other, ie one track goes low to high, the other low to high as you press the pedal.
The other common type is where one track gives half the output of the other.
Both types also tend to have two seperate supplies, one for each track, for redundancy in case of failures.
ECU would do electrical fault checks on each track and a plausibility check between the two tracks.
Don't forget it could be a wiring/connector issue as much as the pedal itself.

 

[mercmancdi]

If it were me , I would find out the cost of the part you think is at fault (from MB) . If it wasn’t expensive I would get your garage to fit it and see if that sorted it .
If the part is expensive I would travel to an Indy with Star before throwing parts at it .
If you have breakdown cover what about calling them out for a diagnostics check ?

+ 1 for breakdown cover if you have it let them have a go at your house as long as light is on

 

[Crazy Mike]

Update. Decided to go down the breakdown route. The engine warning light came on earlier in the day but the time the breakdown arrived the light decided to remain off. No problem as 2 codes were stored DTC 1222 & DTC 1234 "Accelerator pedal position sensor". He also checked the plug and wiring for anything odd but all ok. That has given me confidence to order the pedal assembly.
The error codes match what my own diagnostics picked up (see initial post) but couldn't identify as they had 0000 after them. The breakdown guy said he had seen this before on these W211's. The parts guy at MB also said it's not an uncommon part request.
Hopefully a new pedal assembly will fix it. Will update later.

Thanks for all the good advice given here.

 

[Crazy Mike]

Final update - The new accelerator pedal assembly was fitted (very easy !) and c200 miles on and no warning light. So that's fixed it.
On the old unit, it looks like the actual potentiometer could be removed and replaced but MB tell me they only supply the whole unit (no surprise there) and not just the pot. It makes me wonder if a squirt of switch cleaner may have saved me some ££ !
Thanks again to all those who helped here.

 

[W1ghty]

Final update - The new accelerator pedal assembly was fitted (very easy !) and c200 miles on and no warning light. So that's fixed it.
On the old unit, it looks like the actual potentiometer could be removed and replaced but MB tell me they only supply the whole unit (no surprise there) and not just the pot. It makes me wonder if a squirt of switch cleaner may have saved me some ££ !
Thanks again to all those who helped here.

That’s a good result buddy