Q: I bought my friend's one-owner, well-maintained 2005 Honda Pilot with 138,000 miles on it. It runs really nicely, but while I was driving it recently the Drive (D) transmission indicator light started flashing. I pulled over and found the trans fluid to be full, clean and smelling fine.
The flashing D light went out soon after and hasn't come back on, but the trans hesitates on the first drive of the day and has kind of a "soft neutral" occasionally when going around corners. My cheap code reader didn't show anything, but I'm concerned nonetheless. I know you are busy and haven't seen/diagnosed the vehicle, but I would like to ask you two questions. Is a flashing D light a sure sign of impending transmission failure? Do Pilots have transmission issues? I don't want to invest $3,000 more in my $5,000 car.
A: This sounds like a nice vehicle. Hopefully, the issue will be minor. On Honda vehicles, a flashing D4 shift indicator lamp indicates a fault has been recognized by the powertrain control module related to the transmission. The reason your OBD-II code reader didn't retrieve a DTC (diagnostic trouble code) is likely that this fault wasn't considered to be emissions related and you didn't see an accompanying "check engine" light. Many/most transmission faults do fall into this category, and are indicated by an illuminated check engine light and a P07(ASTERISK)(ASTERISK) series DTC, with or without an accompanying flashing D4 light.
Most recognized faults refer to a faulty solenoid (electric valve that meters fluid), sensor (provides shaft speed, pressure or other information), circuit wiring fault, or a hard fault such as slipping clutch, clogged strainer or orifice, or binding mechanism. In cases where a DTC isn't present, a symptom troubleshooting index is followed to diagnose the fault.
Having the Pilot checked by a qualified tech, using a pro-grade scan tool, is key to getting this resolved. If you'd like to take a crack at reading transmission codes prior to this, it's possible to read them from the D4 light, after placing the system into SCS mode, by grounding terminal nine of the DLC (data link connector used by scan tools) with the ignition switch in the key on/engine off position. Terminal nine is the bottom row/left side terminal (consult a DLC terminal image to be certain of what you see). Gently insert a T-pin, connect via a wire to body ground. DTCs will be flashed by the D4 light. These differ from the OBD-II DTC format; codes 1 through 9 will be that many flashes. Codes 10 and above will be a long flash for tens, then short flashes for ones and twos and so-on. Example of a code 26: two long flashes followed by six short ones.
A search of the web will bring up folks complaining about the Honda BVLA five-speed automatic transmission used in your Pilot, which is certainly better than the BVGA unit used during the previous couple of years. My Honda transmission guru, Roland Dickason, owner of H&A transmissions, a leading Honda/Acura transmissions remanufacturer, says this model transmission isn't a big seller! He expressed optimism a scan tool check might uncover a minor issue such as sticking solenoid. I'd get moving on this right away to lessen the chance of causing damage.
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Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at email@example.com; he cannot make personal replies.