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Hybrid OwnershipQuestionCommunity Starter

Gen 3 Prius rough cold start plus slow coolant loss

TrailRoadie70Community StarterSep 4, 20262013 Toyota Prius ThreeNew York
Older Prius has developed a rough shake for a few seconds on some cold starts and the coolant level seems to be dropping slowly. I don't want to assume the worst. What test sequence would separate ignition, EGR/intake issues and an internal coolant leak? Appreciate any ideas on what to check first. What am I missing?
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13 replies

CleanNerd68Community StarterCommunity StarterSep 4, 2026permalink
Ask what changed right before it started. Capture voltage while the 2013 Toyota Prius is actually failing — after it restarts you've lost the clue. If the cheap test changes it, stop and reassess. A shop burned me once by skipping that step. Not interested in a five-hour wait for a shrug.
PistonTraveler4Community StarterCommunity StarterSep 4, 2026permalink
Same neighborhood, different next step: If a shop can't duplicate it on the 2013 Toyota Prius, bring a video plus freeze-frame data, not just a story. You'll know quickly if you're on the wrong tree. This is from a 2013 Toyota Prius in New York. Post the numbers (or the code) and people can get more specific. I refuse to clear codes until someone else sees them.
TruckMomCommunity StarterCommunity StarterSep 4, 2026permalink
Intermittent stuff lies if you only catch it once. Swap the cheap/easy piece first on the 2013 Toyota Prius and see if the fault moves. Don't erase codes until someone who can help has seen them. On “gen 3 prius rough cold start plus,” that was the fork that mattered for me. This is from a 2013 Toyota Prius in New York. The universe charges extra for guessing. Trying not to diagnose from the couch.
QuattroSellerCommunity StarterCommunity StarterSep 4, 2026permalink
Start with the test that can prove you wrong. Two 2013 Toyota Priuss can feel identical and have different causes, so measure before you copy someone else's repair. You'll know quickly if you're on the wrong tree. Verbal 'we'll take care of it' is not a plan. I've seen both outcomes, which is why I'd test instead of assume. I keep a notes app thread for this now.
TrailRoadie70Community StarterCommunity StarterSep 4, 2026permalink
Checked the easy stuff on the 2013 Toyota Prius and found one clue worth chasing before I book a shop. I keep a notes app thread for this now.
QuattroSellerCommunity StarterCommunity StarterSep 4, 2026permalink
This is usually cheaper to test than to guess. Capture voltage while the 2013 Toyota Prius is actually failing — after it restarts you've lost the clue. If the cheap test changes it, stop and reassess. This is from a 2013 Toyota Prius in New York. I'd want that in writing, not as a promise. Only after sitting overnight so far.
TruckMomCommunity StarterCommunity StarterSep 4, 2026permalink
I'd want a measurement, not a hunch. Write temp, speed, and in-gear vs coast when the 2013 Toyota Prius does it — then decide on parts. You'll know quickly if you're on the wrong tree. The universe charges extra for guessing. I already checked the easy fluid levels.
NewCarMomCommunity StarterCommunity StarterSep 4, 2026permalink
I wouldn't throw parts yet. Move a coil or plug on the 2013 Toyota Prius if it's cylinder-specific and see whether the code follows. You'll know quickly if you're on the wrong tree. Do that first. I'm keeping receipts and dates in one folder.
TruckMomCommunity StarterCommunity StarterSep 4, 2026permalink
Intermittent stuff lies if you only catch it once. Capture voltage while the 2013 Toyota Prius is actually failing — after it restarts you've lost the clue. Don't erase codes until someone who can help has seen them. On “gen 3 prius rough cold start plus,” that was the fork that mattered for me. Parts cannon is a personality type I try to avoid. I refuse to clear codes until someone else sees them.
QuattroGeek8Community StarterCommunity StarterSep 4, 2026permalink
Same neighborhood, different next step: If a shop can't duplicate it on the 2013 Toyota Prius, bring a video plus freeze-frame data, not just a story. If the cheap test changes it, stop and reassess. On “gen 3 prius rough cold start plus,” that was the fork that mattered for me. This is from a 2013 Toyota Prius in New York. A shop burned me once by skipping that step. This is the version I'd tell a friend.
PistonTraveler4Community StarterCommunity StarterSep 4, 2026permalink
If it were in my driveway, write temp, speed, and in-gear vs coast when the 2013 Toyota Prius does it — then decide on parts. That's the branch I'd chase this week. This is from a 2013 Toyota Prius in New York. Happy to compare notes if your setup is different. Happens in gear, not in park, for what that's worth.
QuattroLearner17Community StarterCommunity StarterSep 4, 2026permalink
Ask what changed right before it started. Write temp, speed, and in-gear vs coast when the 2013 Toyota Prius does it — then decide on parts. That's the branch I'd chase this week. If they can't show the line item, I assume it's hiding. A day of patience here is cheaper than a wrong part. I refuse to clear codes until someone else sees them.
GarageMomCommunity StarterCommunity StarterSep 4, 2026permalink
I wouldn't throw parts yet. Two 2013 Toyota Priuss can feel identical and have different causes, so measure before you copy someone else's repair. Save the big job until that test fails. Monthly payment math is how wallets disappear. I'm in no rush to be a hero on it.
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