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1994 W124 Error Code 25
Did lots of search and couldn't find much topic associated w/ knock sensor failure. I cleared the code ~ 2 days ago and it came back again today.
My understanding is that K.S hardly goes bad. If that's the case, what else can trigger the code ? Any help would be very much appreciated. |
Are you sure you have the right error code? I assume you're getting this from the DM. What engine do you have?
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A 1994 W124 should have an M104 3.2 litre engine.
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104 Eng, 138K miles
Help !!
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Quote:
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Thanks, guys !
talked to the local Indy Mech - he has no clue. Then talked to the dealership Mech - he thinks that it maight be related to foul S plugs. S plugs were replaced less than a 1,000 miles ago....makes me wonder if this is related to wiring harness issue.
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<< plugs were replaced less than a 1,000 miles ago>>
Did you use Plats ??????????? He may be right. |
No, I used the copper...
Update - Thanks to Phil (Mercedesshop.com), I got hold of an image of knock sensor !
Came home from work, disconnected wiring harness that was attached to the K.S module and started the engine. I expected the check engine light to come on, but to my surprise, no light. I even used a long screw driver and tap on the engine block to emulate pinging :silly: . Nothing..... Next step - will drive the car and see what happens. |
KS will bring up a code 25 if the sensor calls for full 12 degrees retard.
You can check the sensors outut w/scope and tapping near it with a metal tool/hammer. It is a piezo crystal that sends an ac signal to the ECU. If it is open or unplugged . it will fail the self-test and pop the code. |
Thank you very much, Arthur !
Got to love this forum....
Now I see what triggers the K.S. You said to test it w/ a scope. Any written procedures that I can access to ?..would like to ensure that it's the sensor that went bad before ordering a new part. Again, thank you very much for your help. |
[QUOTE=last993;1273779]Got to love this forum....
Now I see what triggers the K.S. You said to test it w/ a scope. Any written procedures that I can access to ?..would like to ensure that it's the sensor that went bad before ordering a new part. A/C coupling Amplitude-50mV/div Time base -1 mS/div Auto-trigger. I have been told that a simple diyer tool is to use a small speaker or headphones to pick up the audio output , but I have never tried it. I would imagine it works the same way you can test a speaker by scratching the leads across a 1.5 dc flashlight battery... makes sense. I will try it next time I have one laying around. You actvate the piezo [ Knock sensor] by tapping something metalic near its vicinity... no need to have key On power , as the sensor is an a/c crystal generator when vibration activated ...............this is not to compare to scope testing, but it should at least tell one if the sensor is working. |
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