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Flickering check engine light

samm

Member
Hi guys,

This is an interesting one. Check engine light has been on for a few weeks.
I put my diagnostic pin in 19 but there is zero flashes, as if there is no communication with the diagnostic module.
The small 8 hole push button diagnostic thing does light up, although it does not give any flashes when I hold it down for 3 seconds.

Now the CEL flickers while I drive.

Any idea where the pin 19 were actually goes to? So I can trace what's going on?

Many thanks!!

Happy Holidays

Sent from my SM-N950F using Tapatalk
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Pin 19 goes to the DM (diagnostic module), same as the pushbutton and LED in the 8-hole diagnostic block. Could be your DM is failing, it's located under the passenger footwell carpet, the same module is used on all 034/036 models. I've had a couple go bad.

That said, if there are no codes, it MAY not show 1 blink... I wouldn't condemn it for that. I'd also pull the instrument cluster and make sure the correct bulb is in the CEL location. If the proper bulb is flickering, I'd try swapping a different DM. If you have access to a digital scanner, see if it will communicate with your existing DM.

:cel:
 

samm

Member
Dave

Thank you for responding as usual!

Oh yes I totally forgot about that bosch carb unit...

I will hopefully pull up the carpet and take a look.

So you have had a couple go bad? They just stop communicating? Or was it water damage?



Sent from my SM-N950F using Tapatalk
 

gerryvz

Site Honcho
Staff member
I'm wondering if it could be a bad contact at the CEL wire or bulb. Perhaps you can pull the cluster and physically inspect these items. A bulb swap or replacement with another seldom-used warning light bulb would be one thing to try.

I've never heard of a flickering CEL light before. Generally, if a code is stored in the DM, then the CEL is on solidly when it's on.
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
So you have had a couple go bad? They just stop communicating? Or was it water damage?
One failed such that the CEL was on at all times, even with the key off, and the module was warm... draining the battery. Totally DOA.

I forget the failure mode on the other one, but I think it may have refused to communicate with a digital scanner. Swapped out with good used units and haven't had a problem since.

No water damage or other obvious reasons for the failure, they just died. Thankfully these have zero impact on vehicle/engine operation, their sole purpose is to provide a visual indicator if there is a problem with components that can affect emissions. Some 1992 USA model year cars don't have the DM (or CEL) at all, it was phased in mid-production. The DM was North American only, it was not used anywhere else in the world.

I've never heard of a flickering CEL though, that's a new one...

:tumble:
 

samm

Member
Well that's some great info.

The fact that I cannot get any lights from pin 19 may point to the Diagnostic module being dead. First step would be to visually inspect it and then swap in a working one...

Thanks

Sent from my SM-N950F using Tapatalk
 

samm

Member
Hey guys,

So I installed a different CARB module and the check engine still there.
The light comes on and then flickers and goes off for a portion of a journey, then comes back.

Car is running fine and its just an annoying light!

I am trying to trace the wiring routing from the back of the odometer to wherever it goes to see if there is some loose connection or bad ground or anything out of the ordinary?

I may experiment with different modules (start with LH, I have the 400E one installed right now). Will see and report back
 

samm

Member
I forgot to mention that I am still unable to get any flashes or any light whatsoever from PIN 19.

As mentioned I have installed a different MAS unit but still same issue.

Does any one know if this could be a fault arising from the Base module or perhaps an electrical connecition/

I do not want to have to dismantle too many unnecessary parts to trace all the wiring :-(
 

samm

Member
Re: Flickering check engine light rpm drop 20mph

Hey guys,

this is very interesting.

When it is cold outside and sometimes doing around 20mph (and sometimes when coming to a stop) the rpms drop from whatever rpm the car is at DOWN to around 500 rpm (close to stalling) but never stalls. So you could be doing 20mph then the rpms drop to 500 rpm and up again, a few times. then goes away completely.

Is this some kind of sensor or a misfire that causes such a quick drop in rpm?

I'm suspecting the LH module is cutting or adding fuel to cause this? Maybe the circuit board has some defect that shows up in cold temp?

This happens in the cold maybe once or twice and never happens for the rest of the day, car drives perfectly with full power and comes to a great steady rpm when I stop.
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Is there any sign of the FPR clicking under the rear seat? If you're not sure, pull the rear seat bottom and go for a drive, it's easy to hear with the seat removed. The clicking may sometimes appear after a cold start and then go away, on a module that is in the process of failing. As it gets worse, it will click all the time.

Anyway - I don't know if that would be the root cause of what you describe. Are there any codes on the E-GAS (or T/LLR, for non-ASR) module? Remember that normal idle RPM in gear is 500, while idle in P/N should be 650, assuming the engine is up to operating temp. But the idle should be steady, not oscillating. I'd check for vacuum leaks (smoke test works best) for a wonky idle.

Any chance you got 2 bad DM's in a row? Also check the built-in LED+button at the CAN box which is wired directly to the DM. It's a faint possibility that a problem there could be related to why you are unable to get any blinks. Unless that is where you are checking for blinks, instead of with a hand-held blinker box?

:scratchchin:
 

samm

Member
Hi Dave,

Always appreciate your input.

The MAS/CARB module could be faulty but man I doubt it. I will keep it in mind though.

The fuel pump relay is new but I will definitely listen out for clicking in case its already gone bad.

Smoke test was done a few months ago with the proper machine, perfect, no leaks anywhere.

Fuels pumps, reg, filter all new. Ive replaced a lot of sensors and all distributor parts are new. Never changed the CAM sensor, dont fully know how it would impact this issue but the CAM sensor does send info to the LH module.

It certainly seems electronic in nature because if I quickly stop the car, switch it off and on, the idle is regular not jumpy.

I have a suspicion its the LH module. Maybe a cold solder joint (or whatever they call that) that only shows up in cold outside temps.

I think its related to outside temps being low affecting the module in the CAN box thing and not really the engine block itself being cold. Reason I say this is because this issue doesnt show up if I start the car in the afternoon (in CAlLI) when its warmer outside.

I'll try the other LH module and go from there. Then proceed with a different TLLR module.

The diagnostic push button thing also never flashes anymore, not once or several. It does show red light when I hold it down.
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Forgot to clarify... the fuel pump relay clicking (if present) is caused by the LH module. If you have a different LH module, give that a try (can't hurt).

I vaguely recall reading something about the DM pushbutton not showing any flashes if there are no codes, instead of flashing 1 time like all the other modules. So, it's possible there are no codes. At this point the proper test would be connecting a digital scanner to communicate with the DM and see if any codes are present, and verify the scanner is able to talk to the DM without issues. I highly recommend investing in an SDS if you plan to own 92-up MB's with HFM, LH, or ME injection systems. It will pay for itself quickly!

:cel:
 

samm

Member
Hi Dave,

The interesting thing is that if there are no codes then what is causing the check engine light to come on?

The way it flickers and stuff is telling me that maybe there is a wire issue going on. I need to trace the wiring.

I will happily get a digital scanner, never really known which one to get. Can you suggest one please Dave?

Thanks as always:)
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
The interesting thing is that if there are no codes then what is causing the check engine light to come on? The way it flickers and stuff is telling me that maybe there is a wire issue going on. I need to trace the wiring.
I agree completely - something isn't right. I'd start by pulling the cluster and confirming the light bulbs are in the proper locations, i.e. that the CEL bulb has wire #1 and not a different number. They are easy to mix up. If it's a different wire, the DM is not the cause of the flickering CEL.



I will happily get a digital scanner, never really known which one to get. Can you suggest one please?
In general I'd recommend the Star/SDS Compact C3 setup (usually under $300 now) plus an older laptop designed to work with it - there are a few choices available, Dell, IBM, and Panasonic. The software needs to match if you are building a dedicated system with internal HDD. Vendors also offer a setup with an external USB drive that is supposed to work with any laptop, but there's more of a chance of compatibility issues if you go that route. Generally the total cost all-in is ~$500 including the laptop and accessories, maybe less if you find a good deal. The system takes a very long time to boot, so consider shelling out for an SSD upgrade, but ask the SDS vendor about this before buying. You can't clone the HHD to SSD as it will break the license keys; but if the system comes with keygens, that may be ok. If you ever plan to own a W211 or newer, get a system with Developer keygens. And if you plan to own W212 or newer, you'll need to upgrade to the wireless C4 system. Whatever you get, make sure it "supports HHT-Win" which is required to talk to the W124 and, I think, W210.

Old thread with lots of details:
https://www.500eboard.com/forums/showthread.php?t=2651

I got this setup a couple years ago on sale for <$300:
https://www.aliexpress.com/item/Promotion-High-Quality-Mb-Star-C3-Multiplexer-with-All-New-Relay-Newest-Software-2014-01/1814325853.html?

Seems they are selling the C4 now for the same price:
https://www.aliexpress.com/store/product/2014-Cost-Effective-Mb-Star-C4-for-both-Cars-and-Trucks-with-Xentry-2014-01-Version/1199167_1783909054.html
 

gerryvz

Site Honcho
Staff member
I'm wondering if it could be a bad contact at the CEL wire or bulb. Perhaps you can pull the cluster and physically inspect these items. A bulb swap or replacement with another seldom-used warning light bulb would be one thing to try.

I've never heard of a flickering CEL light before. Generally, if a code is stored in the DM, then the CEL is on solidly when it's on.
I mentioned same thing quite some time ago.
 

samm

Member
Hi again Dave,

Im noting down your entire message.

I do have a CLS55 as well so maybe I will look into the setup that works with that too.

Thank you for the great detail and links! :gsxracer:
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Yup, I bought the C3 kit linked above through AliExpress. They hold your funds in escrow for 30 days so if there's any problem, you can get your money back. After 30 days, the funds are released to the seller. More info here:
https://sale.aliexpress.com/__pc/BhQPgEWPNM.htm?spm=2114.12010108.1000001.2.5f4a77abkF26kx

For the eBay C4 kit, you'd have to ask them to confirm, but they say it doesn't support HHT-Win... if so, it may work on the W124. I'm not sure why they list the 124 as compatible if this is the case. If not using HHT-Win, what software emulates the HHT? I don't know anyone who owns a kit this new.

:scratchchin:
 

samm

Member
Yup, I bought the C3 kit linked above through AliExpress. They hold your funds in escrow for 30 days so if there's any problem, you can get your money back. After 30 days, the funds are released to the seller. More info here:
https://sale.aliexpress.com/__pc/BhQPgEWPNM.htm?spm=2114.12010108.1000001.2.5f4a77abkF26kx

For the eBay C4 kit, you'd have to ask them to confirm, but they say it doesn't support HHT-Win... if so, it may work on the W124. I'm not sure why they list the 124 as compatible if this is the case. If not using HHT-Win, what software emulates the HHT? I don't know anyone who owns a kit this new.

:scratchchin:

Thanks for the reassurance about that website.

Regarding the ebay item, it says suitable for 1989 cars and newer. Ive emailed the seller to see what he says....

Would be great if it could work with w124 and newer w219 and similar.
 

gerryvz

Site Honcho
Staff member
If you read the Exploring the Star C3 thread, it should tell you everything you need to know.

Aliexpress is a totally legit site. It’s related to Alibaba in China, one of the largest e-commerce and cloud infrastructure providers in the world.

The Star C3 is perfectly fine for our 38-pin cars and does include HHT emulation.

It will work in a crude, rudimentary way with 1989 and later cars, such as the 126 560SEC, and early W124 models with M103 six cylinder engines. But you will get the same info on those cars with blink codes.

It works perfectly well, said again, with our 38-pin connector cars (ie all E500Es).

AGAIN, PLEASE PLEASE PLEASE READ THE THREAD and you should learn a lot.
 

samm

Member
Thanks Gerry,

I'll spend more time reading after work hopefully. Just had brief moments of spare time today.

;)
 

samm

Member
hi guys,

I swapped the TLLR (idle/crusie) module and I also swapped the LH module (removed the one that was from a 400E and reinstalled a E420 one) and now the diagnostic module is giving flashes again.

Funny thing is there are two codes stored on the LH module that simply do not want to clear (I tried 3 times to clear them) but they were not on the LH module I just removed.

I'll try disconnecting the battery for a while then see what happens.
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Hmmm. What codes are you getting, and which refuse to clear?

Also, disconnecting the battery won't clear codes or reset adaptation on early LH modules. On late LH modules this will reset adaptation, but I don't think it will clear codes (not sure / can't remember).

:scratchchin:
 

gerryvz

Site Honcho
Staff member
I was under the impression that are different types of codes - some are temporary "soft" codes that will clear with power being removed, and others are "stored" hard codes that require manual removal. Depending on the module and what the fault was that triggered the code in the first place. I could well be wrong on this, though.

Sometimes a failure to clear codes can be a fault in technique.

Also, I would clear all codes that you can, drive the car and see what comes back.
 

samm

Member
Hi Guys,

Yes the codes on the LH module are 4 and 13.

Mass air and the IAT sensor. These were disconnected previously when I was testing them while this LH module was installed in the car (several months ago)

Odd that they dont wipe away on this module when nothing was on the LH module that I literally removed moments earlier.

I appreciate the input regarding the battery disconnection.

I hold the button down for 9 seconds after each code to reset it. It works with other faults, but not here.
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Do you know for certain if the module you just installed had zero codes? If not, it's storing codes from whenever it was last in use. Unplugging the module from the CAN box normally does not clear codes or reset adaptation.

To clear, hold the button for 6-8 seconds, per the FSM. I count to 7. Timing to 9 seconds may be too long.

:duck:
 

samm

Member
The module I just installed definitely had both codes above stored.

I will try holding for 7 secs

thanks Dave
 

samm

Member
its so weird.

So I put in the E420 LH module and I get a totally different code that also refuses to clear.

LH module, Idle control/crusie module, base module, EZL module are absolutely clear, no codes.

At pin 19 (diagnostic) ONLY with the E420 LH module I am getting code 19 (adaptation in LH control unit at limit).

If I put the 400E LH module I get code 4 and 13. They also do not want to clear.

Car drives perfectly and I've been driving it everyday last week and today.

Has anyone experienced this before?

Surely if there was an actual problem it should be the same code showing up at the diagnostic pin regardless of which LH module is installed....? :doh:
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
I'm pretty much out of ideas, but can you post the part numbers of the 2 different LH modules in question? Also, do both have the stock/factory EPROM?

If your LH adaptation is more than ~12% lean, it can trigger code 19 on the DM. If a module has the updated software (via EPROM) that allows more adaptation range, it would let adaptation go 15%+ lean without triggering the CEL.

This is where the digital scanner can help, as it lets you view adaptation values on each module.

Persistent LH codes 4 (MAF) and 13 (IAT) will remain until you are able to clear them. If not clearing with the blinker box, it may need a digital scanner to clear, OR the module may have failed where it's not allowing the codes to clear (never heard of this though).


EDIT: Remember, the DM is just a messenger. It only knows what other modules tell it. If one LH module says "yo, everything is cool"... no CEL. Pop in a different LH module that says "Danger, Will Robinson!"... you get a CEL.

:blink:
 

samm

Member
Hi Dave,

I'll get the part numbers as soon as I open up the box again.

So if I install a 3rd LH module then maybe I'll get yet another code (or none!) :D
 

gerryvz

Site Honcho
Staff member
I agree completely - something isn't right. I'd start by pulling the cluster and confirming the light bulbs are in the proper locations, i.e. that the CEL bulb has wire #1 and not a different number. They are easy to mix up. If it's a different wire, the DM is not the cause of the flickering CEL.
Have you pulled the cluster and confirmed that everything is OK and in the right place, and connections are secure? And that the cluster ground is OK?
 

samm

Member
By the way it doesn't flicker now.
Just goes away or stays on.

The other day I reset the adaptation of the LH module. The CEL went for a few mins and then returned :doh:
 

samm

Member
interesting thing I found last weekend. Although I replaced all vaccum hoses on the car, there was this rubber elbow behind the ETA that looked fine but was actually cracked.

I found it by investigating when I could hear a hissing sound that came and went every few seconds near the power steering pump area. So I used a vacuum pump (mityvac) on the vacuum hoses. Vacuum was held with the hoses on their own. But when I added the elbow vacuum was lost.

Anyway, maybe this triggered some fault code many times?

I read that the LH module would store codes but then reduce the number of occurrences by ONE every time there was no problem? Something like that.

Well I had reset LH adaptation after replacing the faulty vacuum elbow and CEl came back in a few minutes.

I must say I really like driving this car! Driven it for several days in a row with no probelmos, thankfully. Many many parts have been changed in my spare time. Hopefully can figure out this annoying CEL. EU cars dont have these CEl right? So I would be totally happy if this was a German market car :D
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Do you have a photo of the hose in question? The only hose behind the ETA is about 1 inch diameter and routes to the back of the passenger valve cover (part of the PCV system).

Only North American market cars have the DM and CEL. The rest of the world did not have either. Japan had an exhaust temp warning in place of the CEL. All other countries had nothing at all.

:roadrunner:
 

samm

Member
Hi Dave,

I dont have the pic. But its that small rubber elbow that connects to the 4 or 5mm vacuum hose that goes right behind the ETA. It is the vacuum hose that leads back to the EZL unit.
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Hi Dave, I dont have the pic. But its that small rubber elbow that connects to the 4 or 5mm vacuum hose that goes right behind the ETA. It is the vacuum hose that leads back to the EZL unit.
AH! Got it. Yes, there is a tube that goes from the bottom/rear of the intake manifold, to the EZL. There should only be 2 rubber connectors, one at the intake manifold, another at the EZL itself. If there's anything in between, it's a patch for a broken tube.

If you apply vacuum manually via MityVac to the EZL side, it should hold vacuum. If you apply to the manifold side, it won't hold vacuum, as it's just pulling air from the manifold (open air). With the engine running you want vacuum present at the EZL with no leaks in the tubing. Does that make sense?

BTW, vacuum leaks will cause LH adaptation to be a little screwy...

:strawberry:
 

samm

Member
absolutely makes sense Dave, thanks!

Yes on the manifold side it didnt hold air. So I disconnected the entire hose and blocked it with my thumb. Tested a band new vacuum hose with the same method and it held the vacuum. With the cracked rubber elbow tube attached vacuum was lost quite rapidly.

Yes I had read that code 19 on the diagnostic module can be due to air leaks. The car is running great in stop and go traffic, full acceleration, slow driving etc.,

Im hoping LH will do some measurements and just go away as I read on some manual that the count is reduced by one everytime the car is started without any issues causing the adaptation to reach its limit.
 

samm

Member
Ive got the ETA idle set to a higher idle speed.

The normal setting has idle very low and it makes me edgy in traffic or coming to a stop. So I adjusted the screw in the ETA to set a slightly higher idle. I wonder if that could be triggering the CEL, will look into it
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Just curious, has your NSS ever been replaced? Idle speed in P/N is 650, idle speed in gear is 500. You should not see idle speeds lower than 500, assuming your tach is accurate. Again, this is where a digital scanner is handy, it will show you RPM's with ±10rpm accuracy.

The T/LLR module controls idle speed, you cannot "tweak" this via throttle linkage adjustments, without risk of causing other problems. Are there any codes present on the T/LLR module?

:cel:
 

samm

Member
Hi Dave,

yes Neutral safety was replaced with genuine.

I turned the idle screw and my idle is always slightly higher. (maybe 100 rpm more in park and probably the same in drive).

My idle in drive is never at 500 and there is no hesitation. Nice and solid
 

samm

Member
I just read on another forum that someone kept getting code 19 on DM and "another EPROM" was the fix?

I need to read about what the eprom is
 

samm

Member
hey Dave,

I just found a post you worte in 2017:
"The modified programming with increased adaptation (to ±32%, up from stock of ±25% according to the FSM, or ±16% according to other sources) is ONLY, and I repeat ONLY, for the 4.2L engines.

Someone who shall remain nameless sells these chips for "all" LH M119 including 5.0L which is just plain wrong; the seller does not understand the chip also includes fuel delivery mapping which varies by displacement. :doh:

If you are getting DM code 19 your mixture is either too rich or too lean. You cannot verify without a digital scanner that will show the adaptation values from the LH module.

Also, keep in mind this problem only affects USA models with a CEL and DM module. The ROW do not have this and nobody would have a clue if their LH adaptation was near limits. Since the system is OBD-1, CA smog testing cannot tell when the DM was last reset, so if you can keep the CEL off for a few restarts, you can clear it just before going in for the test. However it could be indicating a problem that could be the cause of your smog failure due to high HC.

And, a bad O2 sensor could be causing this as well..."
 

gsxr

.036 Hoonigan™, E500E Boffin
Staff member
Yup! That is accurate info. It's possible the modified chip will cure the DM code 19 problem, but equally possible something else is causing the issue in the first place and the modified chip would just be a Band-Aid covering the real culprit.

On the bright side, since the car is running great, I wouldn't lose sleep over it! Especially if fuel economy is normal. A digital scanner would be a big help in this particular case.

:bartman:
 

samm

Member
Hi Dave,

I know you have mentioned the digial scanner several times.. hint hint to me :p

I have reached a small delay with that because I am now lloking for a star diagnostics that will work on a w124 and a w219.

Yes I read that MAF and O2 sensors are the two that give readings for the self adaptation.

my o2 sensor is new. I have a refurbished Bosch MAF that I could try and see if that helps the readings going to the LH module.

Do you know of the EPROM is soldered in or is it a pressed in chip?
 
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