Hello everyone,

I made the famous Arthur Dalton code reader last night and gave it a try on my 1990 300ce M104 24 valve (124.051)

I found a copy of a large PDF file that supposedly has the code tables for my car (apparently it accompanies the "CS1000" fault code scanner). The frustrating thing is that this document does not list the function of many of the active pins in my 16-pin diagnostics unit.

The built-in code reader gives me code 17, which is "02 sensor shorted to positive or ground". I get 4 different codes on Pin 6, which is SRS according to the above-referenced document. I get 7 different codes from pin 14.

When I look at the tables, my car does not show anything for pin 14. On page 28, it shows a number of w124 models in my year range, but it doesn't list 124.051. It's for the Continuous Fuel Injection system.

Socket 14 for the 1992 and up w124's is for the Cruise Control/Idle Control w/o ASR.

The codes on pin 14 that I pulled are as follows, assuming that I should use the table on page 28.

Code 2: Fuel Pump Relay not Functioning
Code 3: TN/TD Signal (RPM) Interrupted
Code 4: Output for o2 sensor heater control defective
Code 5: output for air injection pump control defective
code 6: output for kickdown switch control defective
Code 12: output for A/C compressor control defective
Code 13: excessive A/C compressor clutch slippage

These codes actually do make SOME sense. I had a mechanic pull the same code 2 about a year ago. Although I replaced the MAS Control unit, which should've resolved that.

Code 3 is jargon to me. What does "TN/TD" mean?

I'm not sure what code 5 means, either.

Thanks for your help.

Pin 14 on a CIS-E car is the MAS relay...most codes are for "current" draw issues & most of the time mean very little.

TN/TD signals are for RPM signals from the EZL or outgoing signals to other modules.

IS the car having any ISSUES?

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Given the amount time since the codes were last checked you should just erase them all and start over.

Thanks for the responses.

MB Doc- the car is indeed having problems. I have a pretty severe "bump" or "hiccup" at idle. In other words, the car idles smoothly, except for a single abrupt shake that occurs erratically. I assume this same issue is contributing to horrible hesitation when accelerating from a stop. It's when I start accelerating, the the car shutters and misses until I get to about 2,500 RPM and the car takes off as if I turned on a jet pack or something. After 2,500 RPM the car is as smooth as can be.

The CEL is on, the code is "O2 Sensor Shorted to Positive or Ground". O2 sensor is new. What I've read on this forum is that a vacuum leak could cause the fuel mixture to lean out, which will confuse the O2 sensor and trip this code. This code has been coming up for well over a year, and I've reset it many times.

Another symptom is that I MISERABLY failed emissions last year and my gas mileage is very poor. One shop leaned out the mixture to the extreme, which made the car run like crap, but got me through emissions with flying colors. Then I brought it back to my regular mechanic, who had to bring it back to a rich condition.

To me, the fact that I failed emissions conflicts with the hunch that my mixture is too lean due to a vacuum leak (which could trip the O2 sensor code). You'd think my emissions would be clean if I'm not burning enough fuel.

Relevent parts that have been replaced (not necessarily to fix this problem in particular) over the last 3 years:

1. MAS Control Unit (which makes the pin 14 codes baffling, but I probably need to reset them as deanyel said)
2. 02 Sensor
3. Plugs, wires, rotor distributor, coil (note, the car seems to be going through plugs unreasonably fast)
4. all injectors
5. OVP relay
6. Cleaned ICV, hoses were flexible and seemed new, ICV wasn't very dirty
7. Head Gasket and Valve Job
8. Mechanics have adjusted the mixture many times, which usually helps for a week, then the problem comes back.


I don't have the tools or patience to test for vacuum leaks, so I'm bringing it into the shop and having them do it. I basically told them I'm not asking them to diagnose my CEL and idle/hesitation problem. I'm simply paying them to find a vacuum leak. Otherwise, as history has proven, mechanics will spin their wheels trying to diagnose this problem and will throw thousands of dollars of parts at it (none of which actual resolve my issues), which is obviously expensive (not to mention wasteful). I will have the shop really focus on the intake mainfold as well, not just the hoses.

I have a very very basic understanding of cars, but my next hunch, if they prove there are not vacuum leaks, is to test the EGR valve... correct my logic if it's wrong: If the EGR valve is stuck open or partially open, or if the computer/module/whatever that drives the EGR is telling it to open incorrectly, this would cause a "vacuum leak", would lean out my mixture, and cause the idle/hesitation issues. I'm not sure if this would explain my poor mileage and rich-smelling exhaust/emissions issues though.

I might just be to the point right now where I will sell the car. I hardly drive the damn thing and it's a money pit. (But I love it so much )

PS- Dean, thanks for your ongoing support, I really appreciate it. I'm sure you've already saved me a lot of money!