Did a search on the forum but cannot find any direct information.

I got a 2-4-1 code and the EGR Controller is not passing vacumn. The EGR Controller will pass vacumn if I connect it to 12V directly. The connector coming from ECM has 12V but no GND when I run engine at 1500-2000RPM.

It seems the ECM is bad? Does anyone has a ECM pinout diagram?

The car is a '91 940GLE with a 16 valve engine. Thanks in advance for any information.

 

https://blarf.homeip.net/greenbook/a...p112?size=full

cause of fault 241
https://blarf.homeip.net/greenbook/a...p113?size=full

https://blarf.homeip.net/greenbook/TP32043_1

 

Thank you for the info, here is the latest:

1. Removed EZ116K Ignition ECU and found output transistor dead (Bipolar NPN transistor). Replaced transistor with 2N2222a from Radio Shack.
EGR Output Transistor
2. Now the EGR Vacumn Controller has power and pass vacumn. But it is always on.
3. The EGR Temperature sensor is working with good ground.

It seems that the EZ116K ECU is bad or the new transistor is not the correct one?

 

I was able to fix it in the end. The local store identify the transistor to be a Siemens BC635-16. The Siemens transistor pinout was reverse of other manufacturers. So here was the process.

1. The 2N222a was the wrong pinout. So the fix didn't work.
2. Found the correct sub but mis-read the Siemens datasheet. So 2nd time didn't work.
3. Insert the transistor (non-Siemens) flat spot facing 180 deg. The fix worked.

Original transistor
New transistor

I became an expert in removing the dash bottom covers and removing the Ignition ECU box. A new Bosch 0 227 400 147 was quoted $1000 and I spent $1.99 on a transistor.

 

But the big question is ; how did you find the bad transistor ?

 

I was checking the wiring continuity from the Vacuum Controller to the ECU connector and found the pin location. Althought pin one was not marked on the ECU connector, if I count this connector from one end, I could match it to the pin number on the material you referenced, pin 15.

I then traced back from the connector and there was a transistor on the board, T740. And indeed this transistor was open between pins. Normally transistors acts like a diode and open circuit in one direction and close circuit in the opposite direction between pins.

Here are the details:

EGR Circuit
Pin 2 of the EGR Vacuum Controller (upper right) is tied to 12V on the key switch.
Pin 1 goes into pin 15 on the Ignition ECU. Diagram show internal T740 transistor switch to GND.
The EGR Temperature sensor is in the EGR pipe. The ECU use the sensor to tell if gas is going thru the EGR valve or not where temperature rise when gas is flowing and cool when the gas is shut off. In the EGR Circuit Diagram, it is the left lower block connected to pin 14 on the Ignition ECU.

EGR Transistor
The Vacuum Controller is connected to Collector side of the T740 transistor (top of the transistor diagram). The Emitter side (bottom side of the transistor diagram) is connected to Gound in the ECU. When the ECU MPU (big chip with many pins) decides to pass exhaust gas, it pulls the Base pin (left middle pin) of the transistor to 5V. This enables the transistor and shorts Collector to Emitter or turn on this switch. You can see the Siemens pinout is reverse of other manufactueres and created great confusion for me.