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Thread: Flickering check engine light

  1. #1
    Senior Member samm's Avatar
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    Flickering check engine light

    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

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    Re: Flickering check engine light

    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.

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    Re: Flickering check engine light

    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?



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    Re: Flickering check engine light

    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.

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    Re: Flickering check engine light

    Thanks for the tip Gerry!

    I'll Also check that..

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    Re: Flickering check engine light

    Quote Originally Posted by samm View Post
    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...


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    Re: Flickering check engine light

    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

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    Re: Flickering check engine light

    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

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    Re: Flickering check engine light

    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

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    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.

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    Re: Flickering check engine light

    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?


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    Re: Flickering check engine light

    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.

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    Re: Flickering check engine light

    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!


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    Re: Flickering check engine light

    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

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    Re: Flickering check engine light

    Quote Originally Posted by samm View Post
    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.



    Quote Originally Posted by samm View Post
    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/Prom...14325853.html?

    Seems they are selling the C4 now for the same price:
    https://www.aliexpress.com/store/pro...783909054.html

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    Re: Flickering check engine light

    Quote Originally Posted by gerryvz View Post
    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.

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    Re: Flickering check engine light

    Quote Originally Posted by gerryvz View Post
    I mentioned same thing quite some time ago.

    Thanks Gerry! I guess my brain must have stored your suggestion from back when you made it

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    Re: Flickering check engine light

    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!

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    Re: Flickering check engine light

    by the way Dave,

    is this website https://www.aliexpress.com/store/pro...783909054.html a legitimate one? Have you used it before?

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    Re: Flickering check engine light

    I know you may not have time right now but I'd appreciate your input on whether you know this will work with a 95 E420? I know it would work with a w219 CLS.

    https://www.ebay.com/itm/V2018-9-MB-...zd3:rk:40:pf:0

    had a look at the d630, very reasonable price 100 or less for refurbished.

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    Re: Flickering check engine light

    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/BhQ...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.


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    Lightbulb Re: Flickering check engine light

    Quote Originally Posted by gsxr View Post
    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/BhQ...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.


    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.

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    Flickering check engine light

    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.

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  36. #24
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    Re: Flickering check engine light

    Thanks Gerry,

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


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    Re: Flickering check engine light

    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.

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    Re: Flickering check engine light

    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).


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    Re: Flickering check engine light

    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.

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  42. #28
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    Re: Flickering check engine light

    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.

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    Re: Flickering check engine light

    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.


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    Re: Flickering check engine light

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

    I will try holding for 7 secs

    thanks Dave

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