Oxygen Sensor wire to CIS Unit Repair - PeachParts Mercedes-Benz Forum

JamesDean · #1 05-24-2009, 02:04 AM

Does anyone have any ideas on the best way to replace/repair the wire (not the heater wires) that runs from the O2 sensors to the CIS brain?

I have a break in mine somewhere (dutycycle 100% per FSM..I've checked continuity between all the pins and the o2 wire.. and get nothing)

JamesDean · #2 05-24-2009, 01:24 PM

I was actually able to track the wire into the engine bay/computer area...it goes into the main harness and disappears somewhere. I cant tell if it connects to something down the harness later or if it loops back around inside the harness and connects to the ecu connector.

Does any one know if there is something between the o2 signal wire and the ecu?

slk230red · #3 05-24-2009, 02:45 PM

Quote:

Originally Posted by JamesDean

I was actually able to track the wire into the engine bay/computer area...it goes into the main harness and disappears somewhere. I cant tell if it connects to something down the harness later or if it loops back around inside the harness and connects to the ecu connector.

Does any one know if there is something between the o2 signal wire and the ecu?

The easy way to check the O2 control lead is to ground it and see if the EHA current goes negative. Or, take a 1.5v D or C battery, negative side to ground, touch the control lead to the positive side and the EHA current should go up. You can tell either way by how the engine idle changes.

By the way, are you putting your CFI Module in Diagnostic Mode to check the duty cycle?

Arthur Dalton · #4 05-24-2009, 02:56 PM

Old Mechanics trick..

Hold you thumb on the Bat pos post and w/other hand, grab the O2 sensor sig wire that feeds the ECU [ unplug the sensor].
That gets the correct input to ECU so you can monitor the changes as you take your thumb on/off the bat post, confirming ECU is acting on your inputs.
Your body has appriximately thecorrect R factor to do this...

slk230red · #5 05-24-2009, 03:42 PM

Quote:

Originally Posted by Arthur Dalton

Your body has appriximately thecorrect R factor to do this...

Not with my sweaty hands!

JamesDean · #6 05-24-2009, 03:55 PM

Quote:

Originally Posted by slk230red

The easy way to check the O2 control lead is to ground it and see if the EHA current goes negative. Or, take a 1.5v D or C battery, negative side to ground, touch the control lead to the positive side and the EHA current should go up. You can tell either way by how the engine idle changes.

By the way, are you putting your CFI Module in Diagnostic Mode to check the duty cycle?

Hm... I'll have to try that trick you said because, as per the FSM, I got no continuity between the o2 control wire and any of the pins on the cise connector. I even checked with a known working car (90' 300SE) and none of its pins are connected to the o2 sensor.

I dont believe that i have to put it into diagnostic mode for duty cycle. A friend of mine who was helping me adjust it said that I didnt need to. Also, it was reading duty cycle numbers fine prior to something causing it to go to .09v=100% dc. I just checked my friend 300SE and it reads duty cycle fine.

slk230red · #7 05-24-2009, 04:32 PM

Quote:

Originally Posted by JamesDean

Hm... I'll have to try that trick you said because, as per the FSM, I got no continuity between the o2 control wire and any of the pins on the cise connector. I even checked with a known working car (90' 300SE) and none of its pins are connected to the o2 sensor.

I dont believe that i have to put it into diagnostic mode for duty cycle. A friend of mine who was helping me adjust it said that I didnt need to. Also, it was reading duty cycle numbers fine prior to something causing it to go to .09v=100% dc. I just checked my friend 300SE and it reads duty cycle fine.

I could not read Duty Cycle on my '93 2.3 so I posted a thread on this site. Steve Brotherton stated that I had to put my '93 into Diagnostic Mode to read duty cycle.....he was correct. Maybe yours is different.

Duty Cycle 0.0%

From Manual:

@1988 California and
@1991 with diagnostic trouble code
storage:

The CFI control module must be switched over
to output of on/off ratio because the signal for
the diagnostic trouble code (DTC) display is
output as priority.
The output of the on/off ratio is performed once
all the DTCs have been read out and the start
button of the impulse counter scan tool or the
non-locking switch on the diagnostic connector
(California version only) is then once again
pressed (see section m).
The % readout now fluctuates when the engine
is running at normal operating temperature and
there are no DTCs.

JamesDean · #8 05-24-2009, 05:21 PM

Quote:

Originally Posted by slk230red

I could not read Duty Cycle on my '93 2.3 so I posted a thread on this site. Steve Brotherton stated that I had to put my '93 into Diagnostic Mode to read duty cycle.....he was correct. Maybe yours is different.

Duty Cycle 0.0%

From Manual:

@1988 California and
@1991 with diagnostic trouble code
storage:

The CFI control module must be switched over
to output of on/off ratio because the signal for
the diagnostic trouble code (DTC) display is
output as priority.
The output of the on/off ratio is performed once
all the DTCs have been read out and the start
button of the impulse counter scan tool or the
non-locking switch on the diagnostic connector
(California version only) is then once again
pressed (see section m).
The % readout now fluctuates when the engine
is running at normal operating temperature and
there are no DTCs.

Hmm...his article seems to indicate that you must switch the unit to diagnostic mode to see the codes..not the duty cycle:

"The KE controller is accessed on data terminal #3. With the key on, engine off, self-diagnostics is activated by grounding the #3 pin for two to four seconds. Once this takes place, the control unit transmits the codes by itself, grounding the #3 terminal. (Remember that all systems work the same; all you need is a directory of which pins to activate and the code table to interpret.)"

Unless I am misinterpreting him...and he's referring to pin 3 on other connector not the x11 on the fender which is what I was talking about

slk230red · #9 05-24-2009, 05:30 PM

Quote:

Originally Posted by JamesDean

Hmm...his article seems to indicate that you must switch the unit to diagnostic mode to see the codes..not the duty cycle:

"The KE controller is accessed on data terminal #3. With the key on, engine off, self-diagnostics is activated by grounding the #3 pin for two to four seconds. Once this takes place, the control unit transmits the codes by itself, grounding the #3 terminal. (Remember that all systems work the same; all you need is a directory of which pins to activate and the code table to interpret.)"

Unless I am misinterpreting him...and he's referring to pin 3 on other connector not the x11 on the fender which is what I was talking about

Quote:

Originally Posted by stevebfl

Late KE systems have to be put into the diagnostic mode in order to read duty cycle. It takes grounding the diagnostic socket on the passenger side.

If I put my VOM on pin #3 of the x11 plug I get 0.0%. When I put my LED tester on the x11/4 connector and press the switch according to the instructions, I can read any stored codes and put it into Diagnostic Mode, then my VOM goes to 50% Duty Cycle.

It sounds like you know what you're doing. I just didn't want you to chase a false problem if you weren't reading your duty cycle correctly.

So, you're stating that you ARE reading the Duty Cycle, and you have no stored DTC's?

I checked my DTC codes first, then I put it into diagnostic mode to check the duty cycle on pin 3 of the x11 plug.

I had 4 flashes, that's how I discovered my Air flow sensor potentiometer problem, 20 minutes later and everything working correctly.

Good luck,

Dave