Help me diagnose this pls

[Nostradmus]

Hi all.

Total noob here, so pls forgive what comes with that. Ive been trying to diagnose a rich condition with my 2001 W203 C180...M111.951 engine. Did a scan using a Thinkar BD6 scanner and came up with the below pdf report.
I have taken my car for a short drive, idled for the past 30 mins to try and get a reading from the fuel system to show it as closed loop. As I understand it...when the vehicle reaches operating temp, the fuel system goes closed loop, up until then, it remains in the open loop stage, meaning it does not alter actual fuel values. Might be wrong on this.... On the below report engine temp shows 92 deg, which i think should be more than enough for the ecu to get it into closed loop. Short term fuel trims also show zero...but I think that is due to the system stuck in open loop mode. The other thing I noticed is that even when held on a steady rev of just over 2000rpm, the O2 sensor does not go above 0.47v...while at idle it stays on 0.45v. Does this mean the O2 sensor is shot? I would really appreciate some advice regarding this. Thanx in advance
btw...i get no codes indicating a fault.Just a strong smell from the exhaust. Also forgot to mention...even at cold and on start...O2 sensor voltage is 0.45v

 

[Nostradmus]

Anybody pls

 

[DSM10000]

I cannot get the image to open but a non varying voltage on the sensor suggests either it or the wiring is faulty.

 

[Nostradmus]

 

[Nostradmus]

hope this helps...and that it is not the ecu. Voltage varies a small bit when revved up. When I say small, I mean 10mV or so

 

[Bellow]

, idled for the past 30 mins to try and get a reading from the fuel system to show it as closed loop. As I understand it...when the vehicle reaches operating temp, the fuel system goes closed loop, up until then, it remains in the open loop stage, meaning it does not alter actual fuel values.

Irrespective of coolant temperature, if the temperature of the O2 sensor drops below a certain value then the ECU will default to open loop as the sensors are too cold to provide a useful signal. This can happen during idling if the O2 sensor's heating element is inoperative - due to either a sensor or wiring fault. I'd home in on this before anything else.

 

[Nostradmus]

Irrespective of coolant temperature, if the temperature of the O2 sensor drops below a certain value then the ECU will default to open loop as the sensors are too cold to provide a useful signal. This can happen during idling if the O2 sensor's heating element is inoperative - due to either a sensor or wiring fault. I'd home in on this before anything else.

Thank you for this. I got my ramps back today....so will get her up on the ramps tomorrow. Im going to remove, clean and do some testing on the cables...hopefully its something small. A friend is going to drop some sensors here tomorrow, so I can check those as well.

 

[Bellow]

Thank you for this. I got my ramps back today....so will get her up on the ramps tomorrow. Im going to remove, clean and do some testing on the cables...hopefully its something small. A friend is going to drop some sensors here tomorrow, so I can check those as well.

If I had to ascertain if the heating elements were intact, I'd locate the fuse that supplies them, find where the connection in the wiring to the sensors are and measure the current across the fuse holder (fuse removed) with and without the O2 sensors connected. If the current is higher (and sensible - not short circuited high) with them connected then reasonable to assume the heating elements are intact. The same reading connected or disconnected would point to them having failed or a break in the wiring feeding them.

 

[Nostradmus]

Makses alot of sense....but what about the no show on the STFT?

 

[Bellow]

Makses alot of sense....but what about the no show on the STFT?

Didn't you answer that yourself in your opening post?

. Short term fuel trims also show zero...but I think that is due to the system stuck in open loop mode.

 

[Nostradmus]

Didn't you answer that yourself in your opening post?

Im not sure if that is the case

 

[Bellow]

Im not sure if that is the case

I think it is!
If there's no signal from the O2 sensors there's no data for the ECU to read and without that it cannot tell the level of fuelling so even if it tried to trim fuelling it couldn't. In any case in open loop it won't even try to. It defaults to pre-programmed fuelling values in the absence of O2 signal.

 

[Nostradmus]

So got her up on ramps. Removed the O2 sensor, was pitch black. Took a butane torch to it...and got rid of most of the carbon. Then stuck a multimeter on the heater element and got 10 ohms. On the other 2 wires, I used a multimeter to check the mV reading while heating it up with a butane torch. Took a few seconds, but got a reading which went up to about 900mV and dropped as soon as I took the torch away from it. So this shows the O2 sensor works. Does anybody have the wiring diagram for the 2001 W203 C180 with a M111 engine? Im assuming the heater wiring is fused? Cant see what fuse it is though

 

[Nostradmus]

So...when i remove the sensor, heat it up, it measures voltage according to heat applied, ranging from 100mv-980mv. When I fit the o2 sensor to the vehicle, open the Thinkcar app, it immediately shows 445mv. Any ideas pls...im lost

 

[Bellow]

So...when i remove the sensor, heat it up, it measures voltage according to heat applied, ranging from 100mv-980mv.

It won't be the heat it is responding to but the combustion of the butane torch flame.

When I fit the o2 sensor to the vehicle, open the Thinkcar app, it immediately shows 445mv. Any ideas pls...im lost

They do that!
Mine were putting out about the same without reading anything in particular. The 'measurement' is either side of that voltage.
The heating element appears to be intact so all that remains for that is check that it is receiving the voltage to operate. That should be measurable at the wires at the sensor end of the loom.
I'm guessing there is a fuse in that circuit. On my (non MB) car it supplies the O2 sensor heaters, the MAF sensor, and the EVAP. I found that from the handbook's 'fuse allocation' section. Maybe yours doesn't in which case in the absence of supply voltage at the sensor you'll have to devise another test method - or just replace the appropriate wires (which eliminates any broken wires or shorts).

 

[Nostradmus]

It won't be the heat it is responding to but the combustion of the butane torch flame.

They do that!
Mine were putting out about the same without reading anything in particular. The 'measurement' is either side of that voltage.
The heating element appears to be intact so all that remains for that is check that it is receiving the voltage to operate. That should be measurable at the wires at the sensor end of the loom.
I'm guessing there is a fuse in that circuit. On my (non MB) car it supplies the O2 sensor heaters, the MAF sensor, and the EVAP. I found that from the handbook's 'fuse allocation' section. Maybe yours doesn't in which case in the absence of supply voltage at the sensor you'll have to devise another test method - or just replace the appropriate wires (which eliminates any broken wires or shorts).

I cannot for the life of me figure out where the heater supply comes from, and if it is fused or not. The other 2 wires go straight to the ecu, which I already checked for continuity.
Anybody know where the 02 sensor gets its power from? Or if it is fused?

 

[Bellow]

I cannot for the life of me figure out where the heater supply comes from, and if it is fused or not. The other 2 wires go straight to the ecu, which I already checked for continuity.
Anybody know where the 02 sensor gets its power from? Or if it is fused?

Just (for now) check for supply voltage at the same place you measured the resistance.
Don't know switching regime - maybe live at 'key-on'. For sure live with engine running from cold start..

 

[Nostradmus]

came down with a severe asthma attack, so its gonna have to wait for tomorrow. Will check with a MM and report back. Anybody know where I can get a wiring diagram with regards to the o2 sensors for a 2001 W203 C180?