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Old 07-07-2014, 12:57 PM
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Early W140 - how to read engine light code?

There was a thread on this awhile back, but I cannot find it even using the search, but there is some way you can check the check engine light codes by that thing under the hood on the passenger side (on the early W140). I do not remember how to do this, or how to read the codes. Can anyone help?

Though my W140 is running fine, I think the light being on is hurting me selling it. I called one local shop today and she said they would pull the code for $60.00, but I have to let them know a couple of days in advance. I prefer to do it myself if I can.

Any info appreciated.

FYI - the car has a 4.2L V8 (1993 400SEL)


Last edited by 86560SEL; 07-07-2014 at 10:25 PM.
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Old 07-07-2014, 06:37 PM
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you need one of the so-called home brewed code readers.. you can get them on ebay... with a code sheet.... they can wipe out the codes, too.

if it's your CEL, I would say 90% of the time ...it's an o2 sensor.. which is an easy change...

if your gas mileage has dropped by 20% or so...it is the o2 sensor
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Old 07-07-2014, 09:03 PM
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Thanks. I actually figure it out. Still not sure what the codes mean and we may be speaking of something else, not sure.

I am counting the flashes on the little red light on the box under the passenger side of the hood. I don't think later W140 had these. I cant even find a pic online, but should be able to read code from that light, as it seems like that is why it is there? Not sure though.

Anyway, I had two different codes. One flashed 5 times, then the second one flashed 26 times. I went ahead and reset it and the check engine light is off now, but not sure for how long. Like I said, still not sure what they mean. Car runs fine though.

Someone sent a link and I think that 5 is EGR control module faulty and 26 is upshift delay switchover valve. Not sure what this is, because the transmission works fine.

Thanks again.

Last edited by 86560SEL; 07-07-2014 at 09:15 PM.
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Old 07-07-2014, 10:25 PM
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FYI - the car has a 4.2L V8 (1993 400SEL)
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Old 07-08-2014, 05:27 AM
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That LED light under the hood is only checking the Diagnostic Module (DM) (socket 19 on the 38-pin connector). You have to get the home brew reader to pull the codes on the other modules.

The DM concerns itself mostly with emission-related items. The EGR being inoperative could be a broken vacuum line. The EGR valve is easy to get to because it's right in front, on top of the intake manifold. Check the vacuum line from it as it snakes its way down under the right distributor and air pump and disappears into the passenger front fender area of the engine compartment.

As for the upshift delay, here is a good discussion of it.

Upshift Delay Switchover Valve, Open/Short Circuit (DM Code 26)
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Old 07-08-2014, 04:23 PM
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Thanks for the info. Well I "reset" it and for now the CEL is off.

I will look into those hoses. As far as that upshift delay - if that is where it is supposed to hold in 1st gear longer until the engine warms up, it already seems to do that, so not sure why it is showing a code for that.

I thought the CEL was the reason I was having a hard time selling... now the A/C goes out (I think it is the compressor), so now there is that obstacle. Oh well, the poor gets poorer. lol.

Thanks!

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