Rep Power: 0

2002 Honda Civic, automatic w/ 265k. Front end was very lightly backed into when i stopped behind someone, 30 seconds of driving later i lost all throttle:

• car would start but barely accelerate in drive, while reverse had strong power.
  
• cannot get above 40km/hr
  
• the check engine light and immobilizer "key in ignition" light (green, flashing) came on.
  
• engine stuttered heavily on cold start, but eventually smoothed out (though still not perfect).
  
• transmission fluid was low and burnt. Did a drain and refill — minor improvement but major issues remain
  
• there was some jerking/clunking when shifting gears from park to r/D.
  
• attempted OBD scan, but it failed to connect/communicate w/ ECU after several attemptseven though the scanner powered on
  

so brought the car to a transmission shop. they said:

• the transmission is stuck in failsafe mode (limp mode) and won’t shift properly.
  
• they couldn’t communicate with the transmission computer either (even with their professional scan tools).
  
• after further checks, they believe the ECU/PCU is dead and needs to be replaced.
  
• they said installation of ecu is simple enough that i could do it myself
  
• the tranny mechanic also told me verbatim i wouldn't need to worry about reprogramming/the immobilizer or anything like that (i asked several times)
  
• fuses were checked—none were blown. Battery and grounds seem good.
  

So despite what the mechanic told me and as much as id like to believe it, everything i've read online indicates that i'd definitely have to reprogram or buy an immobilizer/ecu set.

My questions for y'all:

• if I find a used ECU from the same model/year Civic, will it be plug-and-play? or will I absolutely have to reprogram the immobilizer to match the new ECU?
  
• if reprogramming is needed, can any locksmith do it, or does it have to be at a honda dealer?
  
• would buying a used ecu/immobilizer set avoid the need for programming? and would that end up being cheaper than the ecu + reprogramming fees?
• I've been on car-parts.com looking at ECMs but there's no section for immobilizers. Is it to be taken for granted that the ECM listings on there include the immobilizer n keys?

Gratitude!

 
Rep Power: 366

ECU must be keyed to the chip in the key. Most locksmiths can do it.

You will need to check engine type (if you have a D17A2 EX or D17A6 HX, need to be specific to that engine)
Hybrids have different ones too.

Need to be auto transmission as well (manual will not know what to do with the trans).