Do I need a new ECU?

To make a VERY long story short, about a month ago one of my coil-on-plug ignition coils wasn’t firing and a questionable diagnosis by the dealer said that I also needed to replace the ECU.

The new mechanic at first felt that a prior mechanic’s assessment about the ECU was incorrect, because the engine was still running, albiet occasionally knocking out. He later changed his mind, before we could get it running again (he has to fix the problems that the dealer had caused while trying to fix it), and said that its possible that just a few circuits of the ECU have quit working, causing just that one coil to stop firing, even though he’s never heard of that happening before. Is that possible/likely?

Also, where can I find the part number for the ECU for a 1.8L 2001 Nissan Sentra? I can’t find it on

If you need more info and/or have a lot of time to kill, you can read the full saga trying to get my car fixed in American Samoa here:


Whoops. That’s actually Page 2 of the discussion on my car’s problems. Click at the bottom to get to the first page.

I would suspect the ECU is ok though if you can’t get the replacement coil to work on the cylinder that was damaged and the coil was shorted then that section of the ECU may be bad. If the engine is still having problems of quiting on you then you need to verify that the ignition is failing when the trouble happens. The real trouble could also be due to intermittent power to the ECU. I would verify these kind of things are ok before saying the ECU is bad. You should be able to find a replacement ECU for a small cost from a salvage yard I would think if you want to replace it as a test.

I read a recent analysis about just how reliable the components and wiring techniques that are used in todays autos (the motivation of the story was Toyotas “drive by wire” throttle). First forget about drive by wire going away and the amount of redundancy in both the wiring and the components puts the type of failure demonstrated by that University instructor in the “just can’t happen” catagory.

How this applies to the OP? well less dramatic things can happen in components (like foreign materials bridging circuit tracks) would be nice to “stub” in a known good working part.

From what I see you may not need an ECU. The purple wire carries the ignition pulse from the ECM to #2 cylinder igniter and coil. There is a transister in the coil-on-plug to fire #2 spark plug. Without the purple wire connected to the ECM the signel for the transistor to turn ‘on’ and ‘off’ will not be present. If your mechanic has the capability and equipment, he/she should be able to determine if the ignition pulse is on the other end of the purple wire or at least the ECM pinout plug connection. That will verify that the ECM has the capability to fire the coil-on-plug transister.

You mentioned that the #2 coil-on-plug has been rewired. My information indicates that the power to all the coils comes through a 15 amp fuse, through the second set of contacts on the ECM relay, to the ignition noise suppression capacitor, and finally to the B+ common of the 4 coils. It appears that #2 coil has to wired back to where it was. The coil that burned up should not have shorted unless the power getting to it is wrong.

I suspect that a new ECM will not correct the problem. Let me know if I am wrong.

UPDATE (Yes, this is still ongoing): They’ve determined that I do in fact need a new ECU. The one that I am currently using is partially damaged. They had someone bring in a diagnostic machine which didn’t find the ECU at all, although it’s now connected. Meanwhile, he tells me that the car is running but can’t get over something like 2,000 RPM.

I’m now looking for a used ECU. I found a huge list on but another forum I found on Google says that I would be best off finding the VIN, then calling Nissan and asking for the dealer code of the specific ECU that I need before I buy anything. Are they really that different? The guy fixing the car only said that they’d have to reprogram it if it was made for a Sentra in another country.

They’re also having trouble with understanding the purpose of one of the wires, in some way that I can’t quite understand without seeing it in person. The new coils are working, however.