Rep Power: 0

Got a 2019 Si with ~42K miles that's acting funny and throwing some codes, but I'm not sure how to troubleshoot on this. Not my car, I'm just trying to help someone out.


Symptoms:


The car runs smoothly at both high and low speeds. But when I'm doing something like pulling onto an on-ramp and accelerate pretty hard (usually between 3rd-4th gear), the engine misfires a bit until I let off the gas slightly to get the revs down, then it will let me upshift to 5th-6th and it runs smooth.

When it did this, it used to flash a CEL and the scan-tool said it was a 72-1 (Misfire No. 2 cylinder), but it always went away on it's own.


Also, if I would accelerate to cause the misfire and then slow down and come to a stop, the car will be super sluggish when trying to accelerate again. But if I turn the car off and start it again, the problem goes away.


This has been getting annoying, so tonight I took it out on a deserted road and did some acceleration & braking runs, nothing crazy, just typical RPM's and speed for getting onto the highway. On the 3rd test, the CEL came on and stayed on, also got a warning about the hill-stop assist being inop, and the steering warning light is on.


I haven't driven it on the highway since the CEL came on (and stayed on) and all these codes came up, but it drove just fine and felt totally normal driving through town to get back to the house.


Codes:


72-1 - Misfire No. 2 Cylinder

U0401-68 - ECM Failure

U0416-68 - VSA System Malfunction (not having any steering issues at all)


It's got all new spark plugs.


Any ideas what could be causing this, or what my next testing step should be?

 
Rep Power: 222

What brand of plugs and are they gapped properly?
crappy gas?

 
Rep Power: 0

I don't remember the brand name, but they were the more expensive option from O'Reily's. Didn't check the gap on them either.

And the car has just been using regular unleaded, no issues in any of my other cars. Are these supposed to take the more Gucci gas?

EDIT: I will check the gap on the spark plugs now. Thanks!

 
Rep Power: 367

ngk is best for hondas. Bosch, don't go near them, they always cause issues with honda and VW

 
Rep Power: 0

They might have been Bosche lol. I used to live in Germany, probably just picked them for the brand recognition or something.

 
Rep Power: 222

Yep need to use ngk, probably iridium. Rockauto will tell you what the factory plug is. Should say on the gas door or the owners manual what octane to use. And I meant more that your last fill up may have just been poor quality gas like a bunch of water or other crap in it

 
Rep Power: 0

Ah gotcha.

And nope, this problem has been going on for awhile.

ChatGPT suggests that if the ECM is bad, that could be causing a cascade of issues as the 72-1 code for the misfire is typically associated with the VSA system.

Unfortunately my scan tool can only do so much, I think I may just have to bring this to a shop with some more advanced diagnostic software.

 
Rep Power: 367

if they bosch, change them to ngk first

 
Rep Power: 0

I'll do that!

 
Rep Power: 222

What scan tool? I'm used to seeing codes in Pxxxx format

 
Rep Power: 0

I'm using a Foxwell GT65.

Normally it does put out codes in PXXXX format. It does that for my VW's.

Not sure why I'm seeing the Uxxxx and then the weird 72-1 code.

I wasn't sure about it, but ChatGPT recognized it lol.

EDIT: I asked ChatGPT this question, here's what it said:

The reason your scan tool is displaying a code like "72-1" instead of a more commonly known OBD-II code that starts with "P" is due to the nature of the code itself. Here's an explanation of the difference:

1. OBD-II Generic Codes: The codes that start with "P" are part of the standardized On-Board Diagnostics II (OBD-II) system, which is used in all cars sold in the United States since 1996. These codes are standardized across all makes and models. For example, a code like "P0301" (Cylinder 1 Misfire Detected) has the same meaning regardless of the vehicle's brand or model.
   
2. Manufacturer-Specific Codes: On the other hand, codes like "72-1" are manufacturer-specific. These codes are used by individual car manufacturers to diagnose problems that are unique to their vehicle models or systems not covered by the generic OBD-II codes. In the case of Honda, "72-1" refers to an issue within a system that is specific to Honda vehicles, like the Vehicle Stability Assist (VSA) system.
   

The key differences are:

• Scope: Generic "P" codes are used universally across all OBD-II compliant vehicles, while manufacturer-specific codes are unique to each manufacturer.
• Purpose: Generic codes cover common diagnostic criteria across all vehicles, while manufacturer-specific codes provide deeper insights into specific systems or problems that are unique to that brand.

This is why a scan tool may show a manufacturer-specific code like "72-1" for a Honda, indicating an issue that is specific to Honda's systems and not part of the standard set of diagnostic codes used industry-wide. For a complete diagnosis, especially with manufacturer-specific codes, it's often best to consult with a dealership or a mechanic who specializes in your vehicle's make.