Stuck in an open loop - Page 2 - Mercedes-Benz Forum
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#11 (permalink) Old 01-14-2013, 09:35 AM
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The fact that the reading at pins 2 and 3 changed after I unplugged the temp sensor indicates that the computer is responding accordingly.
What happens is that as temperature changes, the resistance changes thus changing the current in the circuit to the computer. The computer uses the current level as it feedback signal.
I will however double check all fuses as I wait for the sensor to arrive in the mail.
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#12 (permalink) Old 01-14-2013, 11:19 AM
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Makes sense, but if the computer changes accordingly when changes occur to the temp sensor, wouldn't that mean its something else?
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#13 (permalink) Old 01-14-2013, 01:07 PM
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Makes sense, but if the computer changes accordingly when changes occur to the temp sensor, wouldn't that mean its something else?
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The computer is detecting the on and off condition of the sensor but isn't detecting the appropriate current levels as the coolant temperature rises or drops.
Something in between isn't registering. The only thing in between is sensor in place and operating.
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#14 (permalink) Old 01-14-2013, 02:52 PM
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Makes sense, but if the computer changes accordingly when changes occur to the temp sensor, wouldn't that mean its something else?
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I don't profess to know exactly what goes on when. I would think it depends on what sensor. Say the Crank Position - during crank you need a min crank speed, when that is achieved the ECU assumes the engine is running and say turns on the Fuel Pump. If the sensor failed, the ECU doesn't know it failed, only no signal so it would not turn on the Fuel Pump. If running and it fails, does it shut down the pump, I think so ???

In the case of the Coolant Sensor - The ECU again doesn't know if the sensor has failed. If the sensor happens to fail and stuck at an Ohm value for Cold, the ECU wouldn't adjust the EHA current for a warm condition or it would it continue to enrich for a cold motor?

No clue how or when the ECU would say it's time for Limp Mode.
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#15 (permalink) Old 01-14-2013, 03:12 PM
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I can tell that there two limp modes. One is when the connection to the temp sensor is lost, in effect an open circuit with infinite resistance; the X11 shows 9.8V at pins 2 and 3.
The other extreme is when connected and the current drawn because of the load due to the sensor's variable resistance at temperature and the current is out of specs, ie outside that curve as shown in post #5; then the X11 shows 2.9V.

I think that I am not achieving a reading within the gray band as shown in the graph. This is my guess.
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#16 (permalink) Old 01-14-2013, 03:15 PM
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The computer is detecting the on and off condition of the sensor but isn't detecting the appropriate current levels as the coolant temperature rises or drops.
Something in between isn't registering. The only thing in between is sensor in place and operating.
DP - Since you have an 88, have you tried making the LED Impulse Box? The manual is not clear, at least not to me. As I mentioned in your other Duty Cyce/ bad O2 thread, I know what I have to do with a 92 Calif car to get into Duty Cycle mode. I have a DTC ( stored codes) and the Button/Led. To get into Duty Cycle mode I have to get and clear any error codes and then hold the button for 4-6 seconds, I know I am in DC mode when both the LED and my check engine light is on ( key is on, engine running ). This applies to Calif cars, 88 up and USA National cars 91 up.

IF I am even close with an 88, you have the X11/4 box at the battery but no Button/Led.

For you there's no DTC or storing of codes but the are current codes showing what ever IF any errors but to retrieve them you need the Impluse LED box.

It doesn't say but I assume once you turn off the key the codes are gone each time and that would be one way to Clear.

For you and why I don't see why one needs the box in the first place, if you see a Steady state at the X11 , for example 50, that's an O2 error. When you pulled the coolant sensor you got what, 30 which is the coolant sensor error. And there are codes for 10, 20, 30, 40 and so on.

Now the manual does say, push the 100% IR button on the Lambda Reader which you or no one else is using. No clue what the button does. Is it doing the same thing pushing the button on the Impulse box? I am just wondering how the no calif version gets into Duty Cycle mode.

I would assume you have to fix any errors first and just like a Calif version, you have to clear after the fix. This applies to testing as well, as IF you pulled a sensor during testing, that's an error and when completed you have to clear.

This is one of the downfalls to the manual as it's not always clear what to do. Just trying to learn, we need someone who have built and used the Impulse box.

Last edited by Logon_Bob; 01-14-2013 at 03:17 PM.
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#17 (permalink) Old 01-15-2013, 02:37 PM
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I am still waiting for the temp sensor but now that I think about it, this issue happened after I installed the new EHA. I am thinking it probably isn't working correctly or the connection to it went bad. I am nowhere near the car right now, that's why I am throwing this idea around...
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#18 (permalink) Old 01-17-2013, 11:36 AM
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I am getting 13.4V DC between the two white wires directly connected to the O2 sensor. Is this normal? I thought the O2 sensor is a just that, a sensor, NOT a load.
Could it be that I wired it wrong? That is, I wired the what was supposed to be the O2 sensor heater to the sensor itself?



Nothing is working in terns of getting out of open loop so far.
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#19 (permalink) Old 01-17-2013, 11:43 AM
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nevermind, the two white wires ARE the heater wires and they are supposed to get battery level voltage.
Back to the garage and measure voltage from black wire to ground.
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#20 (permalink) Old 01-17-2013, 11:48 AM
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nevermind, the two white wires ARE the heater wires and they are supposed to get battery level voltage.
Back to the garage and measure voltage from black wire to ground.
I would also check the EHA current.
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