Ridgeline experiencing mysterious surges

A 2017 Honda Ridgeline. Honda

Q: My wife has a 2017 Honda Ridgeline with a 3.5 liter engine. I’ve noticed that the truck surges, or seems to be searching at various low speeds, during light throttle. You can not only feel it but it also appears on the tach. So it’s not my imagination. There are no check-engine lights, nor have there ever been. At a recent stop at our Honda dealer, I asked the service department if they had ever heard of this, and the answer was no. Our local mechanic says it’s the transmission.

Your thoughts or suggestions?

Dennis in Pa.

A: It can be challenging sometimes to determine if a surge or stumble may be caused by the engine or transmission.

Perhaps you might try this: Find a road condition where your symptom appears such that you can readily duplicate them. Then repeat the drive usiMng the manual shifting mode to hold a gear that results in a slightly higher tachometer reading than before.

Does the symptom go away? If so the transmission may have been downshifting/upshifting, and that’s what you were feeling.

Another check is to leave the transmission selector in auto mode and ever-so-lightly press on the brake pedal with your left foot as you continue to drive normally. This should unlock the torque converter clutch, resulting in a consistent (slightly higher) tachometer reading (assuming no gear shifts occur). If this changes the symptom, it’s likely what you were feeling was the torque converter clutch disengaging/re-engaging when driving normally.

Your torque converter clutch, during light load operation, locks the torque converter to eliminate slippage (slippage is good for power/bad for fuel economy). Most vehicles try to run in the highest gear possible with the converter clutch engaged for good fuel economy. Depending on vehicle speed and load, it’s normal for a transmission to upshift/downshift, and engage/disengage the torque converter clutch at various times. And with fuel economy a priority, there can be a lot of this!

Modern vehicles are pretty smart. In Honda’s case, they employ “grade logic” to minimize excessive gear hunting, but the PCM (powertrain control module) still can’t see the road ahead and anticipate every rise and fall or curve like a human might, avoiding a shift or clutch change as another will soon be needed.

It’s tough to say if you have a problem or if it’s just an unusual road condition your wife may be encountering. With a six-speed transmission and torque converter clutch, there will be quite a bit of gear/clutch juggling as the PCM attempts to provide optimum performance and fuel economy under a variety of conditions. If there isn’t a check engine light, chances are everything may be operating normally.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at bradbergholdt@gmail.com; he cannot make personal replies.

Tribune Wire

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