2001 V70XC - Intermittent ECM 4801

Post by **xHeart** » 15 Nov 2020, 06:53

After the 200,000 miles service the ECM 4801 is playing peekaboo. The MVS search brings up several discussions, but this one with jimmy57 notes is most interesting ECM-4801 Three way catalytic converter efficiency https://www.matthewsvolvosite.com/forum ... hp?t=66635.

jimmy57 wrote: ↑12 Nov 2014, 12:52 The front sensor display is not voltage on that model. Wide band sensors output voltage has a small range of usually less than 100mV and the level of the voltage varies a great amount car to car. The ECM will compare the reference control signal and the signal out to give the display value that VIDA calls lambda and has no unit associated with it. Monitoring voltage of wideband style makes little sense and can't be specified readily as rich and lean so the display of it will be lambda. A direct read of oxygen reference chamber or calibration signal and output by using voltmeter between these two will yield a low millivolt signal that swaps polarity as the out ranges above and below the calibration voltage.
Rear sensor sweeping as binary front sensors do indicates faulty cat if the load is stable. The oxygen level in and out of cat should change with little oxygen remaining if catalyst is functioning. On acceleration the post-cat sensor will show rich (>.75V) as catalyst function diminishes when low oxygen exhaust from extra fueling puts component gas levels in exhaust of range needed for catalyst function. Coasting brings injector fuel delivery stop until engine gets down close to idle speed so the engine is pumping oxygen to catalyst and post cat sensor will register high oxygen content (nearly 0 V). When the load is stable the front sensor will oscillate about stoichiometric, in the case of wideband this means .97 to 1.03. When the front exhaust gas is deviating from stoichiometric in a small range then the catalyst will function well and the oxygen post catalyst will be low leading to the .65-.75 V that should be seen on rear binary sensor.

If power supply is missing for the O2 sensor there would be a code and check engine light. The ECM does amperage monitoring of the heater in order to determine the pulse signal used to keep sensor heat at desired level. When there is no current draw the ECM knows it and sets code.

Back to original problem: The rear sensor should be monitored while driving at a constant speed on level road to see if the signal settles in a range of .65 to .75 V with only small ranging within those limits. If the front goes below .95, even as low as .75, on hard acceleration and then over 1, even as much as 2 on immediate coast then front would be doing as it should. The speed of the response to throttle apply and release is important. More than 2 seconds would not be good. The rear sensor should go over .75V on hard acceleration and fall below .1V on immediate coast then it is doing as it should. Again the time to register change should be under 2 seconds. It is actually a faster response than that but lag time for scan tool adds a second or more.

The procedure, item highlighted in BOLD, can be viewed live over VIDA during a drive, IT WORKS!

Post by **xHeart** » 29 Nov 2020, 08:55

jimmy57 wrote: ↑12 Nov 2014, 12:52 The front sensor display is not voltage on that model. Wide band sensors output voltage has a small range of usually less than 100mV and the level of the voltage varies a great amount car to car. The ECM will compare the reference control signal and the signal out to give the display value that VIDA calls lambda and has no unit associated with it. Monitoring voltage of wideband style makes little sense and can't be specified readily as rich and lean so the display of it will be lambda. A direct read of oxygen reference chamber or calibration signal and output by using voltmeter between these two will yield a low millivolt signal that swaps polarity as the out ranges above and below the calibration voltage.
Rear sensor sweeping as binary front sensors do indicates faulty cat if the load is stable. The oxygen level in and out of cat should change with little oxygen remaining if catalyst is functioning. On acceleration the post-cat sensor will show rich (>.75V) as catalyst function diminishes when low oxygen exhaust from extra fueling puts component gas levels in exhaust of range needed for catalyst function. Coasting brings injector fuel delivery stop until engine gets down close to idle speed so the engine is pumping oxygen to catalyst and post cat sensor will register high oxygen content (nearly 0 V). When the load is stable the front sensor will oscillate about stoichiometric, in the case of wideband this means .97 to 1.03. When the front exhaust gas is deviating from stoichiometric in a small range then the catalyst will function well and the oxygen post catalyst will be low leading to the .65-.75 V that should be seen on rear binary sensor.

^Very helpful with the workings of the two O2 sensor in our 2001 V70XC, BUT, would someone please rephrase or delineate further the sentence in bold?

Post by **xHeart** » 19 May 2021, 07:59

RickHaleParker wrote: ↑15 Sep 2019, 19:47
xHeart wrote: ↑15 Sep 2019, 18:29 Few warm days and the CEL for P0422 disappeared. The CEL returned today when ambient temp dropped below 77ºF.
Metal contracts when cold and expands at higher temperatures.
Spray some Either around the intake manifold when the engine is below 77ºF see if the engine surges. Or you could do a smoke test when the engine is below 77ºF.

^ FOR REFERENCE.
As the temps are swinging 20º, I've CEL during the morning drive, but not when returning in the afternoon. Do P0422 and ECM4801 intersect?

Post by **abscate** » 19 May 2021, 08:46

Yes they do, about 2/3 down listed page

Post by **xHeart** » 11 Jun 2021, 06:43

Well, our peekaboo with CEL continues. The Air Team says, she is healthy and emission free, i.e., PASSED for another 2 years. The young lad did not think she was 20 years and 206,000 miles.

Post by **abscate** » 12 Jun 2021, 05:40

Clarifier. If you have a leak in your purge system too much O2 in the exhaust can trigger the 4801. I would think fuel trims would code first though.

That bold statement above never got clarified.

The ECM swings the mixture around stoichionetric to give it a lock signal to compare. If the rear OXS is also swinging, it means the cat isn’t working by burning off the excess fuel/ exhaust.

Post by **xHeart** » 18 Jun 2022, 06:39

abscate wrote: ↑12 Jun 2021, 05:40 Clarifier. If you have a leak in your purge system too much O2 in the exhaust can trigger the 4801. I would think fuel trims would code first though.

That bold statement above never got clarified.

The ECM swings the mixture around stoichionetric to give it a lock signal to compare. If the rear OXS is also swinging, it means the cat isn’t working by burning off the excess fuel/ exhaust.

A summer check in...
The temps here are above 90ºF, and CEL is OFF.
Now closer to 220,000 miles, the CEL coming ON during the cooler temps, and OFF during the hotter days is now an annual event. The MPG is close to 18, and a full tank of 93 is worth USD100!

I'd read this thread again, and carefully to uncover next step.

Post by **vtl** » 18 Jun 2022, 08:17

Pretty much you need a new front H2OS every 150k miles and rear one every 200k. It could be a melted/ruined cat, too. In that case I'd go with a downpipe. Considerably cheaper and a bit more ponies and low freq grunt.

Post by **vtl** » 18 Jun 2022, 08:19

Oh, and my MPG is 14 =) Only 1 more than Tundra's. Thanks to almost always cold, short, in-town trips.

Post by **xHeart** » 23 Jul 2023, 12:14

vtl wrote: ↑18 Jun 2022, 08:17 Pretty much you need a new front H2OS every 150k miles and rear one every 200k. It could be a melted/ruined cat, too. In that case I'd go with a downpipe. Considerably cheaper and a bit more ponies and low freq grunt.

The two-year IL Air Team summon arrived in the email. The ECM-4081: Catalytic Converter Efficiency - bank 1 made a friendly visit this time. Why P0422 is a corresponding code and not P0420?