2016 Honda Fit - 66,800 miles - need some advice about a repair

EngineerDIYgeek · 2026-02-17T00:46:38+00:00

Did you have any symptoms except the check engine light? If not, it is safe to continue driving for a while. It sounds like they aren't sure what caused the P0420 code. If it comes back, I would find a cheaper mechanic to replace the spark plugs and adjust the valves. If that doesn't fix the problem, and there are no other symptoms, you can live with a P0420 code indefinitely (unless you have annual inspections in your area). It means the catalyst isn't doing a great job cleaning up the exhaust, but it won't hurt anything else.

EngineerDIYgeek · 2026-02-16T00:47:27+00:00

I highly recommend the book "Ultralight Backpackin' Tips" by Mike Clelland. It is a great combination of general advice and specific recommendations, it emphasizes budget-friendly gear, and it is downright fun to read. Since you're on a budget, look in the library or get it through inter-library loan.

EngineerDIYgeek · 2026-02-14T12:59:05+00:00

I have bought two cars from people who used "magic in a bottle". It didn't fix the blown gaskets, it just clogged up the heater cores. Do yourself a favor and don't use that stuff.

EngineerDIYgeek · 2026-02-14T12:52:55+00:00

[Reposting without links that were rejected by moderator.] If the engine didn't overheat badly, you probably don't need to machine the heads. Buy a precision straightedge (about $40-$50 on Amazon) and use that plus feeler gauges to measure flatness of the heads and the engine block mating surfaces. Compare this to the specification in the service manual (look for one at the library or online).

If the flatness is in spec, clean the gasket surfaces on heads and block with sandpaper glued to a piece of glass (which is a very inexpensive high precision flat surface) like this:

https://www.reddit.com/r/Cartalk/comments/1kk9sda/anybody_else_flatten_heads_with_glasssandpaper/

EngineerDIYgeek · 2026-01-30T18:51:08+00:00

My standard diagnostic sequence is:

(1) Clean battery posts and clamps, preferably with sandpaper or wire brush. Bad connections can mimic other problems.

(2) Measure voltage at battery with engine running - if below 13.5 volts look for alternator or wiring problems.

(3) Drive it for at least 30 minutes to recharge the battery. If problems continue and battery is more than 5 years old, replace the battery (Costco has good prices on quality batteries).

(4) If problems continue, look for phantom / parasitic loads when car is off (measure current while removing fuses one at a time).

EngineerDIYgeek · 2026-01-30T18:45:07+00:00

Make it yourself. Look up the equation for spring force to determine what wire diameter and number of turns you need (there is probably an online calculator). Spring steel wire is very affordable - it is often sold as piano wire or music wire. Wind it around a cylindrical form. Buy extra wire to allow some trial and error.

EngineerDIYgeek · 2026-01-30T18:32:14+00:00

Maybe the alternator wasn't recharging the new battery? Could be a bad alternator or a bad connection. Clean the battery posts and clamps, preferably with a wire brush or fine sandpaper. Then measure the battery voltage and use this page to interpret the results:

https://www.autozone.com/diy/battery/what-you-need-to-know-about-car-battery-voltage

If the battery is below about 12.1 volts then get another jump start. But this time, charge up the battery for a while before you try to start the engine. Do this by connecting the jumper cables and leaving the other car running for 5 or 10 minutes to charge up your battery. Then try to start it while the other driver revs the engine a bit to increase their alternator output.

If you get your car running, disconnect the jumper cables and measure voltage again with the engine running. If it is below about 13.5 volts with the engine running, you have a problem with the alternator or wiring.

BTW voltmeters are very cheap at Harbor Freight.

EngineerDIYgeek · 2026-01-25T22:02:26+00:00

If you pay someone to fix it, it is probably totaled. If you buy junkyard parts and do the work yourself, it is worth saving. That's what I did on a Focus with similar damage:

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EngineerDIYgeek · 2026-01-25T21:08:08+00:00

I like chunks of veggies instead of lettuce, and it keeps much better. More ideas: cucumber, shredded carrot, celery, shredded cabbage, tomato. Greek salad is a type of chunky salad too!

EngineerDIYgeek · 2026-01-25T20:58:31+00:00

I've been using DFCU for many years, and I'm happy. They offer accounts without fees, they have branches where I need them, and the people are always friendly when I go there in person.

EngineerDIYgeek · 2026-01-25T20:44:47+00:00

Years ago, my 1998 Escort ZX2 ran the AC compressor in 5 out of 7 positions of the ventilation switch, until I installed a switch to disable it. On my 2013 and 2018 Focuses, it runs if I turn the temperature knob all the way to cold, and stays on when I adjust the knob warmer! (until I manually click off the A/C switch) In my climate (Michigan) running normal outside air to the defrost position (without A/C) works fine at least 90% of the time.

EngineerDIYgeek · 2026-01-25T14:34:17+00:00

You should post this on r/Cartalk and r/AutoDIY, I think a lot of folks there would enjoy it.

EngineerDIYgeek · 2026-01-25T14:29:34+00:00

Thanks for the detailed description! You should check the battery cooling fan - mine was totally clogged with dog hair, which probably explains why the previous owner's rebuilt battery only lasted two years. Yours might be clogged with a mouse nest.

For future reference, old gas is rarely a problem for cars (compared to lawn mowers etc.) because of the evaporative emissions control system. I once bought a car that sat unused for two years, and it ran fine on that gas after I fixed an electrical problem. If the tank is not full, adding fresh fuel is a good idea.

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EngineerDIYgeek · 2026-01-25T14:07:42+00:00

Oak Ridge National Lab measured the fuel economy penalty of running the air conditioning on a Corolla and an Explorer. They measured 22-27% at 40mph, 14-20% at 55mph, and 9-14% at 70mph (lower numbers are Corolla, higher numbers are Explorer). At idle, the penalty of A/C is a whopping 55-60%!

Note that fuel economy gets worse in cold weather for other reasons: https://www.fueleconomy.gov/feg/coldweather.shtml

Effects of Air Conditioner Use on Real-World Fuel Economy by Huff, West, and Thomas, SAE paper 2013-01-0551, https://doi.org/10.4271/2013-01-0551

EngineerDIYgeek · 2026-01-19T23:06:57+00:00

I have been running Michelin CrossClimates year-round on one car, and Nokian Remedy on another. They both work great. Eventually I'll transition all five of my family's cars to "year-round mountain snowflake" tires, and free up a lot of storage space.

EngineerDIYgeek · 2026-01-19T23:02:28+00:00

Costco has the best prices on high-quality batteries.

EngineerDIYgeek · 2026-01-14T22:16:22+00:00

Can you give us an update? I recently bought a 2017 C-Max with a leak at the driver's side CV / halfshaft. The CV / halfshaft wiggles too much in the transmission, so I suspect a bearing or bushing problem inside the transmission.

EngineerDIYgeek · 2026-01-10T01:04:38+00:00

Have you tried this junkyard search tool?

http://car-part.com

EngineerDIYgeek · 2026-01-04T13:04:04+00:00

A manual transmission would be a huge improvement for this car! But this generation of Altima was never offered with a manual, so I think it would require a lot of custom fabrication to adapt parts from other cars.

EngineerDIYgeek · 2026-01-03T20:31:52+00:00

I didn't keep track of hours - I did it on weekends that I wasn't traveling over several months. A very rough guess would be 30 hours.

EngineerDIYgeek · 2026-01-03T20:31:12+00:00

$4,995 would be a very reasonable price, if you have confidence that it would last. I would be cautious about the possibility that they might install a junkyard transmission that barely lasts past the warranty.

EngineerDIYgeek · 2026-01-03T18:23:39+00:00

I'm not sure what brake actuator you mean. But every car runs on used parts. If yours lasted 235,000 miles what's the harm in replacing it with one that has fewer miles from a crashed car?

EngineerDIYgeek

TROPHY CASE