Trying to read codes from the DLC unsuccessfully

[lonewolf41]

I am still trying to see what if any store DTC's I have on my ECM. My engine is an 5.0 OSi-E (serial 4012110198) using an MEFI 4 (4b I think) ECU. My understanding is that putting the ECU in Service Mode will cause the ECM to flash stored DTC's. I believe it is also supposed to flash code 12 to verify that everything is OK. Well, I am not getting any flashes.

I don't have a MIL, so I created one from an LED and some resistors I had. I essentially made a DIY codemate. I understand that connecting this to terminals E (switched ground) and F (12V power) will complete the circuit needed to get the codes. With the key off, my light glows and I verified 12V across those terminals with a VOM. When I turn the key on (engine still off) the light goes out.

Now I short terminals A & B which puts the ECM into service mode and should flash any codes. I hear the IAC solenoid make a noise when I short A&B so I know it is detecting the mode. Nothing happens. I don't get any flashes of any kind...not even code 12 which I understand should be given no matter what.

My first question is: is it possible to read the ECM this way?
Second question: if it is, what am I doing wrong?

I hate to spend $200 to do something I can do with $0.50 worth of spare parts I have, but if I am unable to get anything out of the ECM, I guess I may just have to.

TIA

 

[alldodge]

Suggest tracing the wires

A - Black block ground
B - White/Black to Pin J2-22
E - Green/Yellow to Pin J1-9 and Pin 8 on engine connector
F - Red/Purple to Pin J2-1 and Ignition relay

created one from an LED and some resistors

How many and what size resistors?

 

[Thalasso]

$200.00 is much cheaper then the ECM if you short it out

 

[lonewolf41]

Suggest tracing the wires

A - Black block ground
B - White/Black to Pin J2-22
E - Green/Yellow to Pin J1-9 and Pin 8 on engine connector
F - Red/Purple to Pin J2-1 and Ignition relay



How many and what size resistors?

My LED is spec'd at 20mA @ 1.8V so I calculated that to mean I need 510 Ohms worth of resistors in a 12V system. I had 330 and 180 ohm resistors laying around so I hooked those in series and got 507 on the VOM. The LED was nice and bright while not being overdriven (tried it out on a portable battery pack first). I also used my VOM to try and detect voltage when the MIL comes on and got nothing with it either.

I will trace the wires and see what I get. Haven't had a change to do that yet. Terminal E (ground) is definitely getting switched by the ECM. I have continuity from it to other grounds when the key is off, but loose continuity when the key is turned on. The last part makes sense as the ECM would switch it on and off to get/flash the codes, etc.

Thanks again for the help.