Hi All,

I'm getting P0700/P0740 again after swapping out the transmission and torque converter. The transmission BDRA came with all new sensors and solenoids. Of note, I put it into a 1998 civic EX which originally had a B4RA. The BDRA looks like an OEM reman from Honda if such things exist? So, I suspect wiring now because the other parts are "new/reman" and very unlikely they are the problem and from what I can tell the BDRA should be backward compatible (it's listed as 1999/2000 Civics)

Backstory is:

I swapped out my transmission (had 185K on it and was starting to shudder) for a one that looked to be a Honda Reman - Got it off Ebay for a good price (and yes it runs like it is new) and for that matter so does the torque converter I put in. I suspect I have a wiring problem at this point as the old parts that are the likely culprits are gone.

• New Fluid
• Fluid Level is Fine
• New Torque Converter
• Reman Transmission (old B4RA replaced by BDRA<--> new one the latter are out of 99 and 00 Civics but from what I can tell should be backward compatible. If someone know differently please holler)

So, I have a few questions as I start to troubleshoot the wiring now:
1) What sensors allow the ECU (TCC) to generate P0740? If I'm chasing an electrical gremlin it would be nice to understand the logic used to throw the code? I will start with peeling back the wires/connector on the torque convertor lock out solenoid fist as it probably is an OPEN circuit if anything. the wiring in that location seems to be strained and bent back i.e. takes a beating the way the harness routes.
2) Can someone share the relevant wiring harness diagram so I can trace the Clutch Solenoid wiring and any other sensors used in generating P0740?
3) I sampled live data and the RPM dipped (200 RPM step) around the time an error was thrown. What sensors does the TCC use to decide to generate P0740? Could and intermittent RPM sensing problem be the source or the problem or is it more a case that the solenoid was commanded to "lock" and the ECU didn't see the corresponding drop in RPM expected so it throws a code?

Lastly if the wiring hunt yields nothing then I suppose I should tap the transmission cooling line for a pressure check - but I highly doubt this tranny is bad. It looks and drives too good and isn't getting hot so seems unlikely to be a transmission pump problem.

 

FSM and a DMM really helps. Look up the diagram for that sensor and also go through the diagnostic troubleshooting.

 

P0740 is a hydraulic system issue.

 

Thanks tony_2018 I will work on reading through the FSM. I finally found a copy online in another forum. I see the pin-outs I was looking for on the PCM and the solenoid resistance values. This gives me the point to check from connector to PCM to rule out wiring more quickly than tearing the harness apart and probing along it's length to find a broken section. I may still have to do that but won't be my first step now - Thanks.

It will be a few days before I can do continuity/ohm tests on the wiring harness to look for Opens/Shorts etc.. Seems like an open or partially broken wire (high ohms) would be high on the list given the PCM can't really detect on open wire from a failed solenoid, clogged port, blocked screen or failed pump etc as they all have the same outcome -- no lockup.. That is probably why it's throwing 740 because it's generic for all things electrical, hydraulic, and mechanical which can prevent lock up and it can't detect a failure to actuate on the 3 solenoids in play Linear, A or B. I get that in practice if the clutch plates in the torque converter and tranny aren't bad and there is pump pressure then it is 99% of the time the A/B solenoid that has failed and if not that then the Linear solenoid. The wiring harness and PCM (Transistors) probably rarely if ever fail - perhaps I'm just that lucky

From what I read there aren't too many sensors/solenoids in play. The ECU commands 1 of 4 states i.e. full lockup, partial lockup, no lockup, and lockup during deceleration. From what I can gather since my P0740 happens at 55 mph and above cruising down the road I'm really only looking at the full lockup case. Both A & B Solenoids should be "ON" i.e. have 12V applied and the linear solenoid should be pulsed for "high" pressure. I would guess the PCM only cares about these items when it determines the error code.

• Main Shaft Speed
• Counter Shaft Speed
• Linear Sol -high and Sol A/B actuated

Outside of the error code happening the fact its shifting gears at the points I would expect kind of rules out the speed sensors and the pump since its not slipping and shifting is crisp.

Thanks
Ian

 

This is what you don't want to know.