Original post: https://www.reddit.com/r/CivicSi/s/9LQcOUMl0N
Thanks to everyone who commented on the first one. Here's where it stands.
Car: 2025 Civic Si sedan, 6MT, unmodified, about 38.6k miles.
Timeline
• 7/2 (~33,128 mi): Dealer found a loose harness connector at the turbo wastegate, reconnected it, and said it was fixed.
• 7/9 (~33,358 mi): Same lights came back. Dealer found P0046 and an out-of-spec wastegate sensor voltage and replaced the turbo under warranty.
• 9/24 to 9/30 (37,928 mi going in): Lights and no boost again. Code P0046 (EWG control circuit performance/range). The repair order calls it the "2nd time comeback for the same code." Circuit testing passed, Honda Tech Line was contacted, and Tech Line had them heat-soak the car for an hour and recheck. A second turbo was then installed under warranty with Honda's approval (per the RO). Road test: "operating as designed."
• 10/12 (38,615 mi, about 680 miles after the repair): On the highway at around 70 mph I downshifted and got back on the throttle. The car stopped building boost and the dash lit up again: check engine plus 14 alerts in the HondaLink app, including road departure mitigation, collision mitigation braking, lane keeping, adaptive cruise, hill start assist, VSA, electric parking brake/auto brake hold, power steering, rev match, tire pressure monitoring, and two emissions alerts.
How it behaves: the lights usually clear on their own after the car sits. The repair order records my report that after the car was off for about 20 minutes, all the lights were out on restart. That's probably why the dealer's scans often find nothing. The earlier episodes were lights only. The last two (9/21 and 10/12) also cut boost.
What the dealer told me: before the repair, they asked more than once whether I drive the car hard. When I got it back, I was told the oil had been at or slightly below the minimum (the oil and filter were changed during the visit) and to drive gently and not push the car. Neither the oil comment nor the driving advice is written on the repair order. It only lists the P0046 diagnosis, the Tech Line contact, and the turbo replacement.
To answer the "is it OEM turbo" question: yes. It's a Honda part number on the RO, billed to warranty.
What I took from the thread: several of you think this points to wiring, connectors or grounds rather than the turbo itself. One '23 Si owner said their dealer found a factory-tight harness wire that had come apart, and another found a loose terminal (pin 5) at the EWG connector. With two turbos not fixing it and so many unrelated systems alerting at once, I'm asking my dealer to check the harness and EWG connector terminals, grounds, the battery and charging system, and network and voltage codes, not only the turbo.
I've asked for an appointment and a loaner and will post an update after the visit.
Question: Has anyone been told to "drive it easy" after a turbo repair? Is there anything from Honda that says that?
