Datto

Hi Everyone,

I'm attempting to diagnose why I'm getting a check engine light in my 98 civic ex coupe with an Auto Trans. When I got it had a busted auto trans so I had it swapped for a working one. A month later a check engine light came on and I took it to a friend at a shop who said it was a bad sensor code, replaced the sensor and after driving it home it came back on again. He says he replaced just about all the sensors and it still remains on. It will only get triggered when it gets to freeway speeds in "D4". Leaving it in D3 and driving up to 45-50 mph doesn't trigger any CEL. Let me note there are no unusual symptoms happening, everything is working perfectly fine. No smells, no hesitation, no gear slipping, no weird noises, nothing indicating any problem.

The OBDII code I get is P0700 and that is all, no other code with it. I've attempted to reset the ecu by pulling the back-up fuse in the engine bay fuse box. It turns the light off but after driving again at freeway speed in D4 it returns. Next I checked the CEL code from the plug on the ECU and it did 7 LONG flashes which was CEL code 70.

I'm kind of out of ideas at this point. Could the reporting unit be faulty? Maybe replace the TCM?

Any help would be appreciated!

goldsy

I guess the obvious question to ask right off the bat is, when you replaced the transmission did you replace it with the same model transmission that was originally there? The reason I ask is because if you have an auto transmission with different gears, your ECU isn't seeing what it's supposed to when you're in 4th gear and it's throwing a P0700 code.

Datto

That is a good question. My mechanic friend replaced it and I assume with the same kind that was in there but not 100% sure. It is also possible some one could have swapped it before with the wrong one (unlikely but the car's past is unknown) so it was then replaced again when it broke with another wrong one. It could have had the same check engine light the whole time with the P/O.

I'll do a bit more research and see what I can find out about that. Is there a easy way to get an ID number of what should be in there to compare with what is currently in it?

94EG8

P0700 is just a generic transmission fault code, it doesn't mean anything by itself. Drive it longer without clearing the code and see if a second code eventually shows up. If it starts throwing P0715 codes suspect the wrong transmission was used. Actually if the vin tag is still attached to the replacement transmission see if the 6th digit matches the vin on the car. If not it's the wrong transmission.