Post how you fixed the issue causing a check engine light and code.

[Snagglefoot]

I thought this could be a clearing house for successful fixes involving problem codes. I’ll go first.

P0171 and P0174. These two refer to lean conditions.

There was a break in the hose from the air filter box.
Not all the intake air was being metered resulting in a lean condition in both banks. This was on a 2009 Honda Pilot with a 3.5 V6.

 

[Kestas]

A long time ago my 98 Ford ZX2 threw a camshaft position sensor code, suggesting the variable valve timing part of the engine was dirty or sluggish. I finally traced it down to the 20W-50 I recently used when I was into thick oils. Swapping it back out to 5W-30 cleared that problem.

 

[LouC]

I got 2 codes on my 2007 Jeep for evaporative emissions leaks, large leak and small leak, replaced the leak detection pump and filter & that cured it.
I got the P013c code for slow response from rich to lean, downstream O2 sensor, found a leak in the exhaust system near the O2 sensor.
I got one code on my 1998 Jeep for a small evaporative leak, found a rotted vacuum line that was the cause.
BTW, using a smoke machine helps find these leaks easily/
I lost the passenger side headlight on my 2007 Jeep a few years ago, the codes led me to a loss of ground, so I added a new ground wire to that part of the harness, and that fixed it
I had stalling, rough running etc on my '98 Jeep, no codes till it finally refused to start, crank sensor code, so replaced that, and it's been fine.
Modern cars need scanners if you want to actually "fix" anything, even things beyond P codes, such as bad grounds, broken wires, etc.

 

[martinq]

P0420 "fixed" with Valvoline Restore and Protect & STP Ultra Fuel System Cleaner?

We had a P0420 (reduced cat efficiency) code pop up in January. I reset it and it came back in a week or two. At some point I added STP Ultra Fuel System Clean to a tank or two of gas. This was a couple months into the first OCI of Valvoline Restore and Protect. Since then the code has been gone, did I "fix" it?

We're 1k into the 2nd OCI of Valvoline Restore and Protect now and another batch of cleaner was ran through at that time. It's been ~4 months since the last P0420.

 

[shortyb]

Infamous P2187 code for the 2010 VW Passat CCTA engine. This could end up being a myriad of issues so fired the parts cannon at the most usual culprits. Nada. Ordered a smoke machine did the entire intake tract. Leaky intake manifold gasket from where one of the bolts secures it to the cylinder head. Only issue was that it wasn't securing it. Seems the previous service(s) for manifold removal ended up stripping the bolt hole for that particular one and it loosened up. Well, since it was stripped, I had to HeliCoil repair the bolt hole. Good solid repair and was able to torque that bolt properly again. No more leak/codes.

 

[BrianF]

Alright, I'll bite. I had posted this years prior but was a long one.

I had my 2017 Ram 3500 6.7 deleted. Used a Bulkydog tuner, 5" flo-pro exhaust (4" kits were back order during covid) but I left the EGR cooler and all plumbing intact but all electrical connectors untouched I wanted to avoid coolant leaks at the riser. I worked off the understanding that the EGR is closed, so no exhaust gas leaks out. I had this work done in early spring.

Come summer, once we started seeing +20c, I would get the CEL every couple hundred km, P0111. Cleaned MAF and MAP with no change. Installed an aftermarket MAP, caused more issues. Installed new Cummins sensors, no change.

Was able to watch IAT (thinking fresh air temp at the airbox) on the BD and it usually read approx ambient, but oddly increased with exhaust brake use. Coinciding with the CEL, it would shoot up 40 degrees then settle back normal.

I talked with BD and they had no reported issues of the sort. I loaded the newest software, no change. They did tell me that the IAT displayed is actually a sensor on the intake shelf near cylinder 5. OK cool, a start.

The sensor was filthy and there looked to be wear.on the harness. I cleaned/fixed it up, no improvement. Swapped sensors, no dice.

I gave up for a while and months later pulled the sensor again. Well ***, it was dirty again. Got me thinking, the tuner turns off EGR, the computer is not expecting to see temperature spikes from EGR use. I fabricated some block off plates that went on the intake horn and under the mixer valve. No more problem.

 

[PandaBear]

There was in incident when an Escort I was keeping (capital E, that sounds a bit weird like I was keeping a side chick) for a while had a lean CEL when I try to accelerate entering the highway. Initially I check for all the problems like vacuum hoses, then ignitions problems and found a dielectric break down spark plug wire, then worn out plugs (the last guy used platinum instead of double platinum for 90k miles), then finally cleaning the MAF seems to fix it.

I think what happened was during normal cruising they use close loop control and the O2 sensor keep things right, and then during WOT acceleration they use open loop and the MAF was reading wrong and caused too lean of a condition and leads to misfire.

The rest of the car was garbage (even part of the engine, like the valve seats often drop without warning), but the ignition control was actually decent. Very simple waste spark system even on a 91, as long as you use the right plug and keep the MAF clean it is simple and durable.

 

[supton]

My '99 Camry, I think it was the last year that it had to pass emissions (ODBII check), maybe, on the way home from the garage it set the light. Looked up the code and it was some valve on the back of the engine. I pulled it out, gave it a stern warning, might have rapped it on the fender, and put it back in. Worked fine for years after that.

 

[iCurious]

These are notorious on these Honda V6 engines.

 

[The_Jeff]

Got a 2002 Saturn s-series, had this cobbled together air injection system that went from an electric pump to the exhaust manifold. Had a code. Was able to disassemble it... fasteners weren't corroded... and literally used a bicycle brake cable in an electric drill to get all the carbon out of the 3/8 or so stainless tube. I think I ran the car with it disassembled as well to get some back pressure to blow some stuff out. Code cleared!

 

[The Critic]

These are notorious on these Honda V6 engines.

All Honda engines.