1992500sl

I have a 1992 500sl with a 16-pole diagnostic connector.

Pole 3 is the Continuous Fuel Injection system.

On Pole 3, I got an error code 34: engine coolant temperature read from ignition control module illogical.

All 3 temperature sensors are new and are Mercedes sensors (1 pin, 2 pins and 4 pins).

Can someone explain to me what that error code means please.

Plutoe

It means what it says. One sensor is providing erroneous data. Are the sensors new or used but new to your car and have you tested all the sensors, bla bla bla
PS Do you have all the wiring diagrams,if not I would start searching.

1992500sl

Yes, all 3 temp sensors are new, mercedes parts.

I do not know what other sensors to test. Please let me know.

Plutoe

post your VIN!

bobterry99

My first step to helping you is to understand the circumstances that caused you to replace all three temperature sensors which generally never go bad.

1992500sl

Hi Bob,

There are two reasons:

The major reason is my simpleton interpretation to the error code 34: engine coolant temperature read from ignition control module illogical:-

My interpretation was that the 4 pins temperature sensor was faulty, giving false signal to the ignition control module, which in turn giving illogical signal to "I do not know what this next item is", which in turn giving error code 34 to pole 3 of the 16-pole diagnostic connector.

The minor reason is that i have learnt, over the years, that generic-made parts are not reliable. Therefore I paid the money and bought the Mercedes parts. However, since I was not 100% certain if the 4-pins temperature sensor, or the 2-pins temperature sensor, goes to the ignition control module, I changed both sensors. And while I was at it, I changed the 3rd temperature sensor which I knew goes to the temperature gauge on the dash.

bobterry99

It's my guess the fault code you have is of no consequence. That's particularly so if you started the engine and read codes for the ignition (diagnostic socket #8) and found nothing. If there are no ignition codes, I would perform the following basic diagnostics to determine if your injection system has some of its basic functionality.

Locate the round diagnostic socket located by the ABS unit on the left inner fender. It has 9 sequentially-numbered sockets. With the engine off and cold measure the voltage between #6 (battery) and #2 (chassis ground). Then measure the voltage between #3 (diagnostics) and #2: this should be c. 70% of the battery voltage (the prior measurement), and any other result indicates a fault.

Next, start the engine and warm it to operating temperature. Again measure the battery and diagnostic voltages: now the diagnostic voltage should fluctuate and be in the range of 30% and 70% of the battery voltage; a fixed number would indicate a fault.

Finally, stop the engine and measure the diagnostic and battery voltages. The diagnostic should be half the battery.

1992500sl

Hi Bob,

(1) I started the engine and read codes for the ignition (diagnostic socket #8) and got 1 flash.

(2) I will do the basic functionality tests once I found the diagnostic socket.

(3) I tested pole 3 (CFI) again. In addition to code 34, I got 3 more codes:-

code 17: oxygen sensor signal were shorted to positive or ground.
code 27: data exchange between CFI control module and ignition control module.
code 29: CFI and ignition control module reading different engine coolant temperature.

(4) FYI: The fuel distributor was rebuilt by German Star in Alabama and the Electro Hydraulic Actuator/EHA Valve is new.

(5) FYI: The ECU module was tested, only 3 capacitors can be changed and were changed.

(6) FYI: Apart from a couple of "jerks" when the car first started in the morning, one day the car runs perfect with good idles.

(7) FYI: but another day, the car would start but when I step on the gas, the rpm would "choke", the car would not accelerate, the engine would misfire, stall and die. Leave the car for 30 minutes, same, start the car, choke, stall, misfire, and die. Start the car again, the car runs perfect !!!

(8) The mechanic said it could be the fuel pump ,,,, God saves the Tsar, or the King, or whatever !!!

Alex

1992500sl

Bob,

I forgot to mention, in regards to Points (6) and (7) above, it may be a "heat-soak" problem with the MAS. Many years ago I remember I had the same problems (6) and (7) with the MAS. The MAS is responsible for so many things. I think 15 to 20 years ago you helped me with a a/c problem traced back to the stupid MAS.

Wonder if all these error codes, and (6) and (7), are all related to a defective MAS.

I should be so lucky.

1992500sl

I found out from reading on the internet that, on pole 14, Engine System Control Module (MAS), there is an error code (code 8) that says:-

Engine coolant temperature sensor signal out of range.

But I read the code on pole 14 on my car and I do not have this error code.

bobterry99

"8" is not a valid code for your engine.

I'll again recommend the tests described in my earlier post as a check of the injection's mixture control.