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Check engine light reset

My 93 E420's check engine light has come on, is there a way I can reset this myself before I pay the dealership to reset it for about $40?

It came on when I forgot to re-connect the sensor on the plastic cover behind the driver's side headlight after removing it to replace a bulb.

I think the '93 still uses pulse readout to display faults. There's an LED behind the battery on the firewall that you use to readout and clear the fault memory. I haven't been able to find it on my car yet, but I know it's there.

Press and hold the button for about 4 seconds to begin readout. The LED will flash a number of times to indicate the fault. When the LED is finished blinking hold the button for about 8 seconds to clear the fault. Readout the faults again. 1 pulse indicates no faults.

Jer is right about the pulse readout, if you search the archives there are intructions on how to read the codes and reset the CE light. One thing though Jer, I do believe that the early 124s do not have the LED pulse relay, I seem to remember that it started with MY92 in the US for the 124. My 1990 500SL had it but it was the first year for any MB. Also as for the location, I remember it being under a black cover on the engine side of the front firewall, in front of the battery. Can anyone else confirm this?

-D

Yes, the KE control unit and the LED (if present) is behind a black plastic cover behind the battery.

Clearing the fault memory will extinguish the CE light because no more faults will exist.

A few months ago I rigged an LED with some alligator clips and drill bits (as male sockets) to read the codes from the SRS. Worked pretty well except for burning out a few LEDs!

Behind battery? The battery for my E420 is located in the trunk. In the engine compartment, where the battery would usually be, there is the black box which I think contains the diagnostic plug and a couple of big relays. Is this where the LED is?

How do I search the archives for resetting the CE light?

Thanks

Sorry it took so long to get back to you, here is what I found:

From another thread (please note that this refers to an E320, for the E420 refer to the picture below, the LED and switch are where the battery used to be):

Quote:

Originally posted by Kestas
Your car has a built-in led/sw at the diagnostic plug for code retieval. No code retrieval tool is needed. It's right there next to the right corner of the battery. It's on the right-side firewall that separates the battery from the engine. It's a little black box with white numbers from 1 to 16. Turn on key and push button (white number 2) - hold for 3 secs, release and count the reply code flashes--- continue on til all are flashed and original repeats. One flash is No Codes Stored..

1 No malfunction in system monitored
2 Heated O2 sensor inoperative
3 Lambda control inoperative
4 Air injection inoperative
5 Exhaust gas recirculation inoperative
6 Idle speed control inoperative
7 Ignition system defective
8 Engine coolant temp. sensor, open/short circuit
9 Intake air temp. sensor, open/short circuit
10 Voltage at hot wire mass air flow sensor too high/low
11 TN-signal (rpm) at engine control module (N3/4) defective
12 Heated O2 sensor heater, open/short circuit
13 Cam position sensor signal from-EZL/AKR ign. control unit defective.
14 Intake manifold pressure at start too low.
15 Wide open throttle information defective
16 Idle speed info defective.
17 CAN Data exchange-Malfunction between control units.
18 Adjustable camshaft timing solenoid-open or short circuit.
19 Fuel injectors-open or short circuit or Emission control system adaptation at limit.
20 Speed signal missing.
21 Purge switchover valve-open or shorted.
22- cam position sensor signal defective.
23- Intake manifold pressure w/ engine running too low.
24- Starter ring gear segments defective
25- knock sens
26- upshift delay switch over valve (SOV) valve open/shorted
27- Coolant temp sensor deviation between sensor ciruits 1 & 2.
28- coolant temp sens.

and from the LH MB injection manual (comes on the factory CD-ROMs:

Thanks alot for your info, tried out your instructions. The LEDs indicate that my car has 5 faults. But 3 of them has already been taken care of a long time ago but I just never had them reset yet.

So how do I clear the faults? Will it extinguish the CE light?

Thanks again.

To clear the fault, call it up and wait for the LED to go on steady. Then hold the button for 8 seconds. The fault will be cleared. Do the same for the remaining faults until one pulse is displayed. That means there are no faults stored. The CE lamp should extinguish when the engine is started.

I have tried, but how do I get the LED to go on steady? What do you mean by call it up?

Thanks.

"Call it up" means to make the LED flash the code. You do this by holding the button for 4 seconds. After the pulse output is complete the LED will come on steady to indicate that the fault has been read out and called-up. Then you hold the button for 8 seconds to erase the fault. Repeat this for every fault in the system (at least those you've rectified) until you get pulse display 1.

Oh I see, I have called up the codes, but the LED does not come on steady after each code has been completed. After "X" number of blinks, the LED goes off till you press the button for another 3 to 4 seconds to call up the next code.

Thanks

Ok, it might be a little different on your model. When I read off the codes on mine with an external LED, the LED comes on steady after each code has been displayed.

Not to get off topic, but Jer I noticed that your sig changed to reflect your new paint job, do you have pics? Give us the details if you would...

-D

I'll start a new thread in the W124 forum for my paint job.

I´m a bit curious about the LED you guys are talking about. My car is a 1992 300CE 24v and there is no LED and no button in it. The little black box with white numbers from 1 to 16 is there. I´m just wondering if I am able to pull codes in my car. Do you guys know in which models the LED is? When does it start in the 124 boddy? -Thanks.

dlefaver seems to know which models have the on-board LED. If you don't have it you can still read the codes with the diagnostic terminal and a pulse counter or an LED and some wires. I'll check the service manual for the specifics for your car.

Not too sure about the CE, I can look it up when I get home today. On my 500SL, the 1st pin on the 16pin connector was the pusbutton and the 2nd pin was the LED. I do believe there is another version of the 16pin connector with no light, so there you would need a pulse counter like ala what Jer mentioned.

Thanks for that. Oh, and Jer.. About my car´s engine temperature which we spoke of the other day.. A bit mysterious.. Now, the temp gauge always stays just above 80 like it should. It must have been just air or dirt perhaps in the cooling system.. ;) I flushed the sytem twice, and that seems to have done the trick. ..-But I´d be grateful for any additional information about the codes.. Thanks.

Glad to hear your temperature woes have been solved ;) Keep her runnin' cool.

I've been doing some digging through my engine manuals and I'm a bit lost. What type of injection system does your engine have? LH or CIS-E?

The injection in my car is a continuous injection( cis ). Mercedes calls it CIS-E. That mainly stands for continuous fuel metering of the injectors.(No electricity in the injectors) Whereas pulsed injections( EFI or LH versions) meter fuel through electrically driven injectors, which are controlled with electrical pulses from the ECU. -I believe mine is a KE-Jetronic, but precicely which version of it I´m not sure. Thanks.

You said you have CIS-E, then you said you have KE. :confused: Tell me which one it is so I can send you the fault code table.

My car has a continuous injection, a KE-Jetronic, which Mercedes call CIS-E. I believe it´s the same thing. Sorry for the confusion.

In the engine service manuals, there seems to be a difference. The CIS-E does not have the microprocessor control that one would find on the KE. Does anyone else know exactly?