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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 54023
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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Marty, MBZ shop specialist..working on a 1992 SL500 with a

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hi Marty, MBZ shop specialist..working on a 1992 SL500 with a simple code "22" 02 sensor. first we replaced the sensor and it came back on in about 5 miles. took it back apart and noticed the chassis side of the connector was cracked (probably why it came on to begin with as the sensor looked fairly new) repaired the harness (properly) and still getting the code. Is there something common on these that we might be missing? we tested the heater circuit and it is working. now the code comes back after about 10 miles. Any help would be appreciated.

Hi, a code 22 is a heater circuit code. You need to make sure you have 12V to the sensor heater. If you have the voltage at the sensor you need to disconnect the connector at the N16 module and check from pin 1 to pin 20 in the connector with your ammeter. You should get between 0.5 - 1.7 amp draw on the heater circuit. If you don't get your readings you either have an open circuit on the ground side of the sensor or a fault with the new sensor.

Customer: replied 12 months ago.
thanks Marty, where is the N16 module? All Data does not call it that..thanks.

Click on the attachment below.

Make sure pin 20 is the heater wire. My diagrams are not consistent.

Customer: replied 12 months ago.
Thanks! i will keep you posted or close the question..Bill

You're welcome, Bill.

Customer: replied 11 months ago.
sorry, to be clear, this is with the connector disconnected, key on and engine off, right? i am not probing these wires?

You should check it while it is connected. Use jumper leads if necessary.

Customer: replied 11 months ago.
ok, that is different than what it said the first time. no worries. thanks

You're welcome.

Customer: replied 11 months ago.
thanks, ***** ***** on, engine off or on?

It probably doesn't matter but I would test it with the key on engine running.

Customer: replied 11 months ago.
ok, there are 0 amps running and key on. we replaced the sensor (again) and it didnt change. also, the ground is good. it is a stud right on the firewall near the module. any thoughts?
Customer: replied 11 months ago.
i tried running a temporary ground to the sensor and it still doesnt toggle. there is power going to the sensor heater. need some direction, please.

Hi Bill, are you sure you are testing the correct wire? What your test is telling me is that the heater is open or there is an open or poor connection in the harness. You can unplug the sensor and run a separate power and ground to the sensor with an ammeter inline to test just the sensor itself. Also make sure that the fuse in your ammeter is good.

Customer: replied 11 months ago.
thanks, ***** ***** sense! i think i get brain fade when working on MBZ. just dont have enough training in them, so my common sense just goes out the window! How late can i get back to you today? we are Pacific Time. thanks
Customer: replied 11 months ago.
also, before i sent the request last night, i noticed that the sensor will toggle at higher (2200) RPM, just not at idle. doesnt that indicate the heater is not being energized, or should it toggle at idle regardless of the heater circuit?

It should switch right when you get back to idle but may stop switching if it idles long enough with the heater inoperative.

I'm in Florida. I'm usually around until about 8 PM EST.

Customer: replied 11 months ago.
thanks Marty. i noticed today that the dash slightly flickers at times. it also happens when you operate the turn signals sometimes..could that be related? is this a common issue? The car is a very nice 80k car, but this is the time where they start to have issues, right? i have voltage at the heater, but amperage is only .2. thanks

The flickering dash is usually caused by poor fuse connections or a bad capacitor on the instrument cluster circuit board. You should first replace the fuses for the instrument cluster. Fuse 1, 5 and 9. The spec on the heater is 0.5 - 1.7 amps. It sounds like you have a defective sensor.

Customer: replied 11 months ago.
Thanks Marty. i did some research on the instrument cluster, too. this will be the 3rd sensor i have tried. we even thought the connector might be bad so i soldered the pins together. i could not find a used connector pigtail. we are using Bosch sensors, do you really think 2 of them could be bad? or am i missing something?

I doubt you are getting bad sensors. How did you retrieve the code 22?

Customer: replied 11 months ago.
thanks, ***** ***** scanner.
Customer: replied 11 months ago.
but i am wondering why the amperage is so low when the sensor heater is probed...the sensor should be what should be drawing the amps, correct?
Customer: replied 11 months ago.

you never got back with me and the case closed..any thoughts? thanks

I agree with you about the amperage but it doesn't seem right that 2 Bosch sensors would be defective. What I meant about the code is which socket in the 38 pin connector are you plugging into in order to get the code 22.

Customer: replied 11 months ago.

ahh, yes, PIN#3

Pin 3 is the power supply and pin 1 is ground. You should have a third lead to probe the other pins in the 38 pin connector to pull codes from the various modules.

Customer: replied 11 months ago.

We are using a snap modus scanner with a clip for the ground. the scanner powers itself and pin #3 allows us to read the code 22 on the snapon screen. let me know, please

That does not sound correct. Pin 3 is just a 12V feed. Are you plugging into the 38 pin connector under the hood?

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