2010 Prius out the blue misfire's P0302 P0304

Ok so this is my wife's car. I fixed a similar issue last year with it. Same codes. Cleaned the air intake, replaced, pcv, and ended up being the spark plugs. Well those should be fine since they're less than a year old. Now we're getting again the codes.

P0302 P0304 and P0300 random missfire. Runs like it's gonna blow up crazy shaking at idle. Feels better under load when test driving.

I've checked the coils, they check out for getting voltage and for good resistance. I also swapped them around and that didn't change where the codes were. Same codes same cylinders cleared and checked codes with multiple different OBD apps and BLE ELM reader.

I've checked the plug in cylinder 2 and 4 looks fine and tests good too.

I've tested fuel injectors with multimeter, both getting power and resistance test good.

I've tested the egr system. By unplugging it and by blocking it with a thin metal plate at the pipe as suggested by AMD car care nut and others.

I'm down to HG blown (which I tested for last year and it showed fine, also no coolant missing that I can tell)

Or ECU issues,

Or intake gasket broke and sucking in extra air. I tried to test this with vehicle running and spray a little water around the gasket to see if it changed rpm but not noticeable and the engine shakes so much it's hard to tell.

Also important note. When I first started working on car as I turned it on and off I'd hear a click in the rear near battery. That drove me to check out the battery. Turns out the tail light was leaking and water had pooled up in 12v battery reservoir. We had heavy rain for 4 days in Hawaii. Water was not covering battery but 2-3 inches of water in bottom. So I spent a day pulling tail lights and sealing them, drying out reservoir, and charging and testing battery which charged and tested fine. Maybe there was some damage to the system somehow that's causing this missfire? Thing is car started and ran pretty much fine then halfway through her outing it started missing and running like crap.

If it was O2 sensor that should throw a code correct? I'm just a little stumped. I'm going to block test since I can't do a compression test without tech stream. I have OBD fusion I'm wondering if there's anything I can run or monitor through that to get more information.

I'm going to block test again and get a scope to look in the cylinders.

 

Just want to add an update. In a roundabout way I found my self back to the battery. While checking for power to the coils and injectors I noticed the voltage a little low - under 12 volts. I checked it at the jump point in the fuse box and to the block. Showed Low. So I went ahead and pulled the battery again. Took it to Oreilly's and had them charge and test it. Turns out it's got a bad cell. Not sure if it was due to the water getting in back there or not, but seems likely. Luckily it's a 1 year old battery with a 3 year warranty so will be swapping it out as soon as possible.

Not sure if it's gonna be the fix for the misfire, but I know that hybrids don't function well with a bad 12v so we'll see. Hopefully will know by tomorrow. I also put some iso heet in the gas tank in case it got water in there too and that's causing misfire. Can't hurt to clean out the injectors a little.

 

I appreciate both of your responses.

12v Battery test now showed good on three separate testers while Oreilly’s showed bad. Can’t explain that.

Here’s the thing I’ve done two tests now for HG and both showing negative. I even did this pretty simple test by pulling plugs and starting engine to turn it over. You can see link below for where I got the idea. It showed no water being pumped out.

I’m preparing to clean the egr system, but if that is the problem. (It’s now showing P0403 egr code) then why didn’t blocking off and/or unplugging the egr system fix the missfire?

I’ll scope the cylinder as soon as I get a scope but the plugs look fine. Not blasted clean like a coolant leak into cylinder would show.

We’ll see what the egr cleaning does but I’m starting to think the ecu got fried from the water getting in by 12v battery but only way to test that is to find a good number match ecu to swap.

Simple hg test below.

 

I appreciate both your responses. Yes the car is high mileage 180k

I’ve done two tests that indicate not a blown hg. I’m trying to get a scope and or compression tester that fits this engine to confirm it.

it’s now throwing P0403 EGR circuit on top of P0300 and 0302 0304.

I’m confused because if it’s egr causing the miss then the block off test should fix the miss but it doesn’t. I suppose it could have blocked the manifold ports but seems unlikely after 10k

I’m planning to deep clean the egr but want to absolutely confirm the hg is not the reason for missfires first.

I plan on getting rid of the car once it’s running right. It has a new hybrid battery and new 12v.

it is unfortunately also one of the early paint failure cars that toyota hasn’t recalled. Not one of the two paint codes that they pay to repaint. But has the exact same paint symptoms.

 

That was one test and I see your point. If it is hg maybe very minor at this point. In which case the exhaust gas test won’t show nor would a regular compression test.

I understand leak down test is way to go. But I have a scope coming and a way to pressurize to look for coolant. In the mean time I pulled apart magnet in egr. The ramp is gouged out so it’s likely the egr is sticking. The valve plunger moves smoothly in and out.

is it possible to just get the magnet? Or has anyone successfully repaired it? Because I’d rather not spend 300 for the toyota egr especially when it’s working otherwise.

 

My issue with hg is typically it’s one cylinder or two next to each other. While rare I suppose it could be cylinder 2 and 4

if the egr was jammed because magnet stuck would that cause misfire?

 

I’m hoping to find a magnet that’s not damaged on a parts car so I can try that first. Unfortunately Hawai’i prices mean a 150 egr kit will be north of 300 and then dealer fees to update another 150.

Before I go that route I’ll check with scope and try to find a good magnet for the egr because the valve itself is moving smoothly. Not sticking at all and traversing whole depth of piston perfectly.

 

Alright so little update here. I'm now 99% convinced it's not the head gasket. I've scoped the cylinders and they look like normal for a 185k car. Carbon buildup, some wear on cylinder walls, etc. but no water/coolant that I can see or steam cleaned pistons. Valves also look fine for the age and wear of motor. Everything seating properly.

But the kicker, and I am kicking myself for not checking this earlier. When the plugs went bad last year I did a bunch of checking and even swapped them between known good cylinders and the code didn't move just like the coils this time. Well turned out they were bad (I opted to try first and cheapest part which ended up being right and well overdue) I suppose even after erasing the code the computer may take some time with car running to sense that the missfire has moved. And possibly with a Toyota Techstream program it may work better than OBD fusion or the other apps I tried. Dr. Prius, and Car scanner.

Anyway long story short I used the old school method. I pulled the plug and coil on both known missing cylinders. I made a lead from ground point that would reach and hooked up plug into coil and coil into cable and both those coil/spark plugs were not throwing spark. I pulled and did same test with cylinder 3 which is showing good on scanner. It threw healthy spark. So I've gone ahead and ordered a set of 4 OEM Denso coils and will try them when they arrive. Very hopeful this solves the issue. I don't know if the P0403 egr code will go away when the car is running properly but I'll wait and see on that one.

Will update when I swap parts and hopefully it's running right.

Thanks for the help!

 

Very happy to report that the car is running perfectly again. Running on all cylinders no pun intended. It was indeed the coils. I did all four Denso OEM replacements. Only two were bad but no point having to dig back into car in a few months when the others crap out.

No check engine light, but still “permanent” codes reading even after clearing. As I understand it they will clear on their own after driving for a while?

Now if I can get Toyota to repaint this terrible failing paint we still have a good car on our hands.

A side note. On the egr magnet I posted with the slot worn into the ramp inside. I ended up going with 2 part jb weld. Scraped the area to rough it up and then lightly dabbing jb weld into the groove and piling it up to proper height to recreate the stop. We’ll see how it holds up but pretty easy to check. I’m still looking for a junkyard swap.