DTC 4201 - Intermittent, and rough running, but NO OTHER CODES!

Post by **packetfire** » 31 Jan 2024, 09:59

2004 V70 non-turbo, well-maintained, 250K miles.

Most recently replaced the J-hose on the EVAP system, as it was leaking (why Volvo put it in such a difficult to access location remains one of the mysteries of the V70), but my mechanic and I loosened a few bolts and dropped the rear subframe down a bit to make room to reach the hose, leaving the exhaust in place.

Two months later, I got a DTC-4201 and a check-engine light while on the highway on a hot day, but no other codes, so erased it and discounted it as spurious. Forgot all about it, did not happen again in all of fall.

The car sat in the garage for nearly all of January, as I was out of town, but it started and drove fine for errands around town on Friday and Saturday.
Sunday, on the highway, heading for church, it ran very rough, sounded loud, and the DIM instantaneous fuel mileage was in the low teens rather than in the 20s and 30s. It ran so rough, I pulled over, parked and called a friend to take us to church as he drove by.

Drove home carefully, still running rough. VIDA reported only the 4801, no other codes of ANY sort, unusual given how rough the car was running. I expected a bad ignition coil, given how bad the car was running, it was just that bad.

Monday, drove around on errands around town for 2 hours, and could not reproduce the problem. The car ran and runs fine. The local mechanic plugged in his code reader, and found the same lack of any other codes, and the sole "4201" error, which reads as a "420" on non-Volvo code readers.

The VIDA counters (see attached screengrab) show:

Counter 1 - Started operation cycles since fault was last found........................15
Counter 3 - All operation cycles since the fault was found the first time........... 1040
Counter 4 - Confirmed operation cycles with active fault.................................. 53

So, this is a VERY intermittent issue.

With no codes at all from the fuel/intake/exhaust system, my mechanic and I are stumped as to how to proceed in diagnosis, but I do not want this thing to start running rough on my twice weekly 1.5 hour drives to visit my Dad, and force me to get towed home.

Should I drive with VIDA connected, and look at the O2 sensor outputs? Why don't I have some "obvious' code if I had such poor engine performance to prompt me to pull over and abandon ship?

Could we have created an intermittent exhaust leak with our J-Hose repair method? If we did, how might a mere exhaust leak make the car run so rough and have horrible gas mileage?

Any suggestions or hints are welcome.

[Edit - Fixed Typo - 4201, not 4801!]

npexcept · Post by **npexcept** » 31 Jan 2024, 10:16

DTC-4801 (ECM-4801) just means that the car detects too much deviation from the catalytic converter efficiency.
A rough running engine will trigger this.

Fuel pressure looks good, so it's not the fuel filter I guess (but also, people rarely take a look at these).
If fuel is good, then it's either compression or oxygen. Compression also unlikely if its running good in general.
Can you take a look at the MAF sensor? A faulty sensor or corroded connector will not always throw any errors,
but it will result in a bad running engine. Since your DIM did show the changes in fuel consumption, your car knows that
something is up with fuel/oxygen. I would dig in that direction.

I dont really know much about your exhaust leak question, so I'll skip that approach lol.

A leak in the PCV system (vacuum leak) could also result in poor performance. But that wouldnt occur sporadically.

spinard · Post by **spinard** » 04 Feb 2024, 13:41

Intermittent problems are terrible, and VERY intermittent problems are the worst. Having Vida at the ready when it happens is a great idea. But I would recommend running a graph, not just data display. You could easily miss an intermittent sensor problem trying to look at just the current value. Don't trust freeze frame data for intermittent problems. Pick the most likely culprits since you can only graph 5 at a time.

This was the only way I ended up tracking down a failing fuel pressure sensor that was causing an intermittent "stutter" (nothing like what you describe, but also not bad enough to set a misfire code). Most of the time it was fine, but occasionally spiked up to the maximum value for a split second.

Final thoughts: From the way it ran, do you suspect it was a single cylinder problem, or something that was affecting the entire engine? If unsure, disconnect the injector and coil for one cylinder and see if that's what it was like (expect a misfire code). If that's what it was like, then focus on things that affect just one cylinder -- coil, injector. Otherwise focus on things that affect all cylinders -- e.g. MAF, fuel pressure, O2 sensors, short-term fuel trim. Rule out things that would not be intermittent (e.g. spark plugs, compression).

Post by **jonesg** » 04 Feb 2024, 14:08

when it happens again unplug the maf and see what you get.

XC70Rider · Post by **XC70Rider** » 04 Feb 2024, 15:25

Your attachment is displaying ECM-4201 (not ECM-4801).

A faulty MAF is one of a handful of things that can trigger the ECM-4201 code so do as Jones suggested and unplug the MAF next time it happens.

Post by **packetfire** » 13 Feb 2024, 17:29

Go ahead and laugh at me - my "rough running" was found - I had a very very bad front brake caliper. It was occasionally refusing to release the brakes, making the "rough running" and the lower fuel economy. Duh!

So, new caliper, and just because I have it up on jackstands again and have the tools out, new brake pads all the way around.

But that random 4201 has come back and been cleared twice now, always lights the check-engine light at highway speeds, so I'm gonna look at some MAF and O2 sensor outputs on the graphing VIDA display.

Post by **jonesg** » 13 Feb 2024, 18:54

you might have damaged the brake disk too, they form cracks and turn blue when over heated.

dikidera · Post by **dikidera** » 14 Feb 2024, 01:13

I personally got ecm 4201 when a lot of oil entered the cat. However just like your car mine also sat 5 months in my soggy garage, then I assembled it, then overfilled oil which entered the cat and have had this code ever since.

Can also be caused by leaky injector according to VIDA I think or it's very clogged.

Post by **jonesg** » 14 Feb 2024, 16:23

dikidera wrote: ↑14 Feb 2024, 01:13 I personally got ecm 4201 when a lot of oil entered the cat. However just like your car mine also sat 5 months in my soggy garage, then I assembled it, then overfilled oil which entered the cat and have had this code ever since.

Can also be caused by leaky injector according to VIDA I think or it's very clogged.

try cat cleaner in the gas tank, burn the oil out of the cat.

https://www.fcpeuro.com/products/exhaus ... lEEALw_wcB

dikidera · Post by **dikidera** » 15 Feb 2024, 09:10

jonesg wrote: ↑14 Feb 2024, 16:23
dikidera wrote: ↑14 Feb 2024, 01:13 I personally got ecm 4201 when a lot of oil entered the cat. However just like your car mine also sat 5 months in my soggy garage, then I assembled it, then overfilled oil which entered the cat and have had this code ever since.

Can also be caused by leaky injector according to VIDA I think or it's very clogged.
try cat cleaner in the gas tank, burn the oil out of the cat.

https://www.fcpeuro.com/products/exhaus ... lEEALw_wcB

Honestly I've done that many times, I've even driven the car in 3rd gear for extended periods of time, the code is on there permanently. Of course the downstream oxygen sensor could also be problematic.