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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 54037
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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My wife's 2008 Mercedes R350 4matic has a very annoying hood

Customer Question

My wife's 2008 Mercedes R350 4matic has a very annoying hood open warning light on the dash that will not go away I have already replaced the hood latch switch and read almost every post on google about others having this same issue. Is there a rely or fuse tied into this switch somewhere? Any help will be greatly appreciated
Submitted: 1 year ago.
Category: Mercedes
Expert:  Marty replied 1 year ago.

Hi Earl, my name is***** are no fuses or relays for the hood switch circuit. The hood switch sends a ground signal to the rear signal acquisition module when the hood is closed. The blue wire at terminal C5 of the rear SAM needs to be checked for a ground signal. If there is a ground at the connector and the hood open warning continues to come on the problem will be either the connector to the rear SAM or a bad rear SAM. If there is no ground going to the rear SAM it would indicate a break in the wiring from the hood switch to the rear SAM.

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Customer: replied 1 year ago.
ok I have located the rear SAM and have identified the wire that leads from the SAM to the hood latch switch. I have verified the connector is good by splicing into the wires and checking the ohms from the splice and at the end of the connectors are the same. How do I check for a ground signal from the Rear SAM the the end of the connector?
Expert:  Marty replied 1 year ago.

Just disconnect the plug at the rear SAM, close the hood and probe the blue wire with one lead of your ohmmeter and connect the other lead to ground. If the circuit is good you will read 0 ohms with the hood closed and OL or infinity with the hood open. If the circuit checks good you will need to replace the rear SAM.

Customer: replied 1 year ago.
ok just checked the wiring and i am getting the opposite os what you said I get 0 ohms when the hood latch is open not making contact with the switch and OL when the latch is pressing the switched closed, is there anyway to trick the system to think the switch is closed by jumping the wires or grounding the blue wire? Anything will help it is driving my wife crazy which is driving me crazy because it just beeps the whole time we or she is driving.
Expert:  Marty replied 1 year ago.

The diagnostic chart may have it backwards. Try driving the car with the switch disconnected. If it still beeps try driving the car with the blue wire grounded. If it still beeps, and you are getting the signals all the way to the SAM, you will need to replace the rear SAM.

Expert:  Marty replied 1 year ago.

Hi, just following up with you on this question. Did you get this squared away yet?