Mopar SBEC PCM/ECM Injecor Driver Repair

Yes, they can be fixed. This is the story of how I repaired the SBEC/ECM in a 1993 Dodge B350 Van with the 5.9 Liter "magnum" engine.

Disclaimer: I may be handy with a soldering iron, but I am not an electronics engineer. This information is provided for entertainment purposes only. While this procedure worked for me I cannot guarantee it is even 10% reliable, much less 100%. Do not attempt on an ECM that you cannot afford to damage, and do not use an a vehicle that you cannot afford to have break down. Please do not email me asking for more information or tips. I have shared what I know below. If you do not know what a MOSFET is or how to desolder, then I cannot help you on those subjects. May I suggest an electronics class at your local college?

Ok, anyway, rant over.... onward!

Symptoms: Misfire, Check Engine Light with "Injector Driver" fault code.

Tools Needed: Multimeter, 1.5 Torx, 2.0 Torx, Razor knife, Needle nose pliers, Soldering Iron, Solder, Solder wick or desoldering tool. Silicone or hot glue gun for reassembly.

Diagnosis steps (check this before you rip into your ECM):

  1. Make sure you have "symptoms" above.
  2. Check each injector with an automotive stethoscope. Confirm which, if any, injector is not firing. In my case it was Cyl #5. If all your injectors are firing, the procedure below will not help you.
  3. Use a vehicle wiring shcematic to find the related wire at ECM connector. In my case it was pin 38
  4. Backprobe that pin a the ECM connector. With key on, momentarily ground the probe and check for injector pulse.
  5. If no pulse, suspect bad wiring and/or injector. If the injector pulses when grounded manually, but not when the engine is running, the problem is in the ECM or ECM connector
  6. Inspect ECM connector. If connector is ok, problem is inside ECM

Ok, so now we are down to the fun stuff!

You will have something that looks like this:
image

Flip it over and on the back side you can see the traces and the leads of the various components. We are interested in the main connector (at top) and the power transistors (at bottom). image

You can identify the power transistors (drivers) near the heat sinks by the typical three pins in a row like this:
image

  1. Using a multimeter, check for contnuity between the offending connector pin from step 2 above and the middle pin of each of the drivers. There were 11 in total on my ECM. 8 for injectors, 1 for coil, 1 for alternator, and 1 for... something else (I forget). Oddly, not all the injector drivers are the same style (some are larger).
  2. If I lost you at step 1, stop here. You are in over your head. Go buy a reman ECM and be happy.
  3. If I am not speaking greek by now, you probably know that a continuity check will isolate which of the drivers is connected to the pin we are interested in. This will be the bad driver.
  4. Carefully cut away the potting compound around the leads of offending driver. Desolder the three leads for that transistor.
  5. Still with me? You do know how to solder, right?
  6. Flip the ECM back over and pry the heat sink locking clips out of the potting compound.
  7. Remove the plastic reatiner and you can now pry out the offending driver.

The bad driver in my unit was made by Harris Semiconductor, Part # 5234847. I could not find much information on this part, but I believe a comparable cross reference would be a NEC 2SK3484. It is a fast-switching N-Channel power Mosfet. I had to wing it a bit to find something similar at the local electronics shop. Closest I could get was NTE part# NTE2388. Cost: $5.79

image

Install the new part and reassemble in the reverse order of above. Thoroughly re-pot all disturbed areas using silicone or a hot-melt glue gun.

Reassemble ECM and install in vehicle. Cross fingers, start engine.

In my case anyway, it worked! Enjoy!