2004 S60 ECM-4801 Cat. Faulty Signal. includes waveform

quietcoolone · Post by **quietcoolone** » 31 Oct 2014, 07:33

Hi,
Purchased an 04 S60 2.5T about a year ago and the check engine light was on for multiple faults including transmission. Fortunately all but one code remains... car now has 122K miles.
ECM-4801 Three way catalytic converter efficiency, bank 1 faulty signal.
Back in March i replaced the Front 02 sensor (Bosh 28851171373), cleared the cel but it returned.
I've cleaned the TB, MAF sensor, replaced plugs and coils, new gas cap seal, cleared the cel but within a few days it was back.
Last week i replaced the downstream 02 sensor (Bosh 28851164887), cleared the code, resent ECM but the cel is back on.
I've searched the forums for help but most seem to point to a bad catalytic converter. I can't tell if the cat is bad but there is no smell or smoke. The car averages 25 gal city, and 30 hway. (93 octane)
i connected VIDA to graph sensor waveforms (take a look at the pictures).
It is my understanding that sensor 1 is upstream (before cat) and senor 2 is downstream (after cat) and the computer uses the upstream sensor to gauge the air/fuel mixture.
Based on VIDA, upstream sensor shows very little or no waveform (straight line), and downstream sensor has constant waveform. Is this in reverse?
Notice the upstream sensor products a waveform only after releasing the gas pedal (See picture 4 & 3), otherwise its basically a straight line.
Picture 2 -- results from disconnecting intake manifold vacuum hose, and picture 1 is with hose reconnected.
I hope the pictures provides a better understanding of what I'm dealing with and perhaps someone can shed some light and help me get this issues resolved. The car is going in for state inspection by the end of next month.
Thanks in advance.

draser · Post by **draser** » 31 Oct 2014, 11:13

My Torque reader shows switching between .1 to .75 volts at idle fully warm about once per second.

quietcoolone · Post by **quietcoolone** » 01 Nov 2014, 15:01

draser wrote:My Torque reader shows switching between .1 to .75 volts at idle fully warm about once per second.

Thank you.
but is your reading on the front or rear sensor?
I'm confused as to why mine switches on rear but nothing from the front.

draser · Post by **draser** » 02 Nov 2014, 11:07

That is indeed the rear sensor. The front one is stuck at 0.25volts either at idle or driving - engine hot.

draser · Post by **draser** » 03 Nov 2014, 06:58

Here are the screenshots..

quietcoolone · Post by **quietcoolone** » 05 Nov 2014, 08:13

Thanks for the help.
You seem to have more knowledge about how these sensors work.
I don't know why Vida shows a waveform for the rear sensor and very little action on the front (this is opposite of what i've seen diagrammed online).
If the cat is bad the rear sensor should mimic the front (same or similar waveform)
The car has power, normal idle, no smoke, no hesitation, and great gas mileage --- and i don't know what else to check, fix or replace in order to get rid of the cel one and for all.

Thanks.

draser · Post by **draser** » 06 Nov 2014, 08:38

What voltage level is the front stuck on? As far as behavior mine work the same.

quietcoolone · Post by **quietcoolone** » 07 Nov 2014, 09:31

According to VIDA the displayed number for the Front Sensor is not voltage.
So i borrowed a scanner from a friend and took some freeze frame data pictures . This is right after the CEL came back on.
Let me if this is helpful.
Also, the voltages vary 0.2V- 0.7 V on one sensor and -0.012 to 0.02mv (very low) on the other

draser · Post by **draser** » 08 Nov 2014, 07:46

Looking at voltages the first one seems to be for rear sensor and second for last, correct? The second voltage level is way low so I'd look into connectors and harness condition. With meter plugged in have someone wiggle wiring around to see if volt level changes.

draser · Post by **draser** » 08 Nov 2014, 10:56

Forgot to mention the ground connection for sensor 1 - easily tested with ohm meter on x1 scale measuring between sensor body and ground point on either shock tower. Should read zero ohms.