Not getting any hits on another thread, so I will re-post here:

1990 300te
California Car, 147,000 miles, 124.090 body, engine 103.983

Ok, I built Arthur's home brew code reader as a project with my 10-yr old son. It came out great and works like a charm. Tested the car, found tons of codes (most are probably old), cleared them one at a time and then drove some errands.

Upon return I got the following:

Pin 3 - 17 Oxygen sensor is shorted to positive or ground
Pin 14 - 3 TN/TD signal (RPM) interrupted

I have 2 questions:
Is pin 3 picking up the same Oxygen sensor fault that I get when I use the built-in diagnostic unit on my car that reports on the emission system?

What does the message on the Pin 14 fault mean?

Thanks in advance.

Pin 3 addresses the same DM as the built-in Led for Cal versions.
Pin 14 is a TN signal glitch...try coearing it again and then see if you get a singler Flash on that module..if you do, them clear the memory on that one.

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A Dalton

Arthur, thanks for the reply.

Yes, I was able to clear the Pin 14, fault code 3 with the code reader. Now a single flash on that pin. I will test drive tomorrow and report back with findings.

So what is a TN signal glitch anyway?

After 10 minute test drive, 3 flashes on pin 14 has returned.

What is it and how to correct?

Shameless bump.

Anybody know what this error code means and how to correct?

Pin 14 - 3 "TN/TD signal (RPM) interrupted"

Did you do the Memory clear I posted?????????????

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A Dalton

Yes.

I got 3 flashes, held button down for 8 secs, there was a click and a single flash. Then key off.

To test I keyed on and held for 2-3 secs and got a single flash.

I assume that meant that all was clear on pin 14.

You have only cleared the codes. I need you to clear the MEMORY .


After single flash [ which signifies Fault CODES cleared ], wait 2 secs , hold for 5/6 secs , turn key OFF for 50 secs , On for 10 secs , Start car.
That clears any glitch in the MEMORY.

If the code then comes back , you have an engine speed signal fault and can address it then . If not , you are OK w/memory reset.

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A Dalton

I have done as you instructed. After starting the car, I show just one flash on all the pins. I will test drive tomorrow and report further results.

One question though; I did this procedure tapped into pin 14. Would this need to repeated to clear the memory on each code or does one time wipe all codes out? (just in case for the future)

Each module is reset individually and none can be reset until a single flash confirms there are no codes stored.
I had you do that one b/c that is where you are having a problem and I will not get out test procedures and schematics until I know your Memory has been reset b/c it could be a simple memory glitch ..that's all.

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A Dalton

Arthur,

After test drive today, fault 3 on pin 14 has returned. I cleared the code and then cleared the memory per your instructions. When I turned off the car, I checked and the code 3 was still there.

To be sure, I repeated this two more times. Same result. Now what?

Ok

Having a litle trouble finding info on that chassis b/c it is MAS controller Cal version w/16 pin diagnostic box. Kinda rare combo.

But , I did find TN signal code and I would first check this sensor and the wires from/to it.. and take fuse #7 out and clean the ends and the holder.. [ or spin the fuse a few times in the holder]

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2GN17VPXQ2GN17XWT3&yearid=1990%40%401990&makeid=MB%40%40MB%40%40X&modelid=300%2DTE%2D001%40%40300TE+Wagon&catid=F%40%40Engine+Electrical&mode=PA&subcatid=F6010@@Reference+Sensor&source=www.peachparts.com&clientid=catalog.mercedesshop

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A Dalton

Fuses have all been recently cleaned.

Do you know which sensor this error code covers? (or both)
What is the procedure to check the signal from these sensors?

What is the source of documentation to troubleshoot these codes? ( I have all of the MB paper manuals and the MB WIS software)

I have noticed that since I tried to clear the memory today, the car is behaving differently. Before it turned over immediately. Now it takes longer to start and I have to give it gas. The idle seems very weak.

I don't have info on that model w/cal version.

I believe the front is speed sensor and the rear is crank sensor.
That info should be in your docs somewhere.

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A Dalton

I will check my MB manuals.

Bottom line, if I forgo any testing/troubleshooting and just replace both sensors, will the issue be resolved?

Any sense on why my idle has changed after doing the memory clear procedure?