Rep Power: 0

I have 2003 civic LX that I just removed a broken BMXA from and installed a JDM SLXA. My OBD II code reader shows that P0740 comes up as soon as I get to 50mph. The car drives perfectly, but I guess the slight difference in gearing is the reason for the code. I am getting ready to take it in for a smog check, but the EV light (evaporation system) on my code reader is flashing after I clear the P0740 code. All other emission readiness monitors are fine. From my understanding, in CA, all monitors need to complete their cycle, with the exception or the evaporation system(page 4 of https://www.bar.ca.gov/pdf/Smog_Chec...ll_Version.pdf). Assuming everything else is fine, is the car ready to pass smog if I keep the speed down on my way to the shop prevent triggering the MIL?

If I do need to fix this to pass, will swapping to a JDM ECU prevent this p0740 from returning? The car is non-vtec, so I assume a non-vtec ECU would be needed. I think the chipped key may have issues with a new ECU. Im not even sure CA smog will accept an JDM ECU. Anyone have experience with this?

 
Rep Power: 228

The ecu needs to match your car for 3 categories

-vtec option
-auto vs manual
-2001-2003 vs 2004-2005

And be the Jdm variant that supports your gear ratio.

 
Rep Power: 0

Excellent. Didn't realize there is a difference for 01-03 vs 04-05 ecu. I have no idea what my JDM transmission came from. Is there anyway to identify those details from its serial #?

 
Rep Power: 228

Are you sure the sensors are OEM on the rebuilt transmission?

Try looking for part numbers on them or a denso logo.

It's possible the ecu is reading a value it doesn't expect because an aftermarket sensor is installed. (Hondas are known to not like aftermarket sensors)

 
Rep Power: 0

Everything looks OEM, but will take a closer look. Just replaced a leaky solenoid and the TRS from the original onto the JDM.

I passed smog this weekend with no problems, just needed to clear code then drive a bit under 50 mph to the shop to prevent it coming back.

This SLXA's gearing is definitely a little different from the BMXA, so the p0740 code makes sense that is thinks the Torque converter is not properly locking up. It tachs a little higher on the freeway with the SLXA.

 
Rep Power: 118

I have an SLXA trans in my 05 with a matching JDM PCM and I love the gearing, it feels a bit quicker. I'm honestly not sure why these cars set a P0740 code when a SLXA trans is installed with a US PCM. P0740 is a torque converter clutch circuit malfunction code, so basically an electrically faulty lockup solenoid or wiring problem. a P0741 is the code it sets when the circuit is intact, but the TCC doesn't apply correctly when the PCM commands it However, people have swapped the lockup solenoid to the US one and still have the same code, so I'm not sure. It would seem that the PCM should be setting a P0741 code though.

From my understanding, the gearing wouldn't cause it to set a torque converter lockup code. From my understanding, the PCM monitors the input and output RPM of the torque converter and sets a code if the torque converter's output RPM is lower than the input RPM, which would indicate slipping. However, simply changing the gearing shouldn't cause the PCM to detect a difference in the input and output RPM of the torque converter.

My best guess would be that the RPM pickup for the mainshaft speed sensor in the transmission is a little different, causing the sensor to not read the RPM the way the US PCM expects the sensor to read it.

Or maybe Honda took an unconventional approach to determining torque converter slippage where the PCM compares engine RPM to speed and sets a code if the engine is running at a higher RPM then what the PCM expects at a given speed instead of comparing torque converter input and output RPM. In that case the gearing would cause it to set a code because the engine RPM would be higher than what the PCM expects it to be at a given speed. Who knows