CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

PO740 check engine light on but no trans problems evident

Took my '01 Civic LX 1.7L automatic w/ 156,000 miles to a transmission shop to be looked at for check engine light on with PO740 code. Needed to get car thru inspection. Transmission has shown no problems. They dropped the fluid, that did not turn light off nor did switching out lock-up solenoid. They’re talking rebuilding the trans due to possible internal damage. That’s hard to justify in my mind w/o obvious drive problems. They saw on the computer diagnostic the problem that turns on the light is intermittent. Check engine light has gone out as recently as April for a while. Can just the torque converter be replaced? Will that or doing other rebuild steps definitely clear check engine light? This place can’t guarantee it. Over years light has been on for gas cap, catalytic converter, now this. What’s my next step?

Do not have your transmission rebuilt if there are no symptoms to suggest a problem, there will be afterward. Again if there are no symptoms there would be no reason to have your torque converter replaced either. Is your torque converter locking up at highway speeds? Do you know what that means? Perhaps the shop you are going to has exhausted their level of expertise as it applies to your Honda transmission and you should find a new place to go to.

You mentioned you had the fluid changed. If I owned a Honda I would be darn sure they refilled my transmission with genuine Honda ATF, nothing else, no alternative. Despite what some may say, I am a big believer in manufacturer specific fluids, especially with Hondas.

The DTC (Diagnostic Trouble Code) P0740 is for “Torque converter clutch solenoid circuit [problem}”. The problem is about an electrical situation, right now. It could involve other things; but, that won’t be known until the electrical checks are done.
I’m sure that alldata.com has a troubleshooting chart for this code (P0740). Search for a shop which can/will troubleshoot this problem.

I’ll double check the fluid they used. Thanks for the tip. You’re the 3rd person that said if it ain’t broke don’t fix it. I may try taking it to my dealer.

I read about the solenoid circuit on-line, asked the transmission shop about that, and their reply was if they changed the solenoid that should have done it–basically ignored/dodged the circuitry question. I’ll seek an electrical check and let you know, maybe at my dealer as some have suggested, who see these cars all the time.

Sorry I forgot to say before that I have heard talk of having torque converters locking up at highway speeds, but don’t know what that means nor how to tell if my car is doing that. What I can say is it drives just fine and still gets about 35 mpg mixed driving. I can ask that transmission shop tech in a follow-up phone call or the next place I take it to.