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High and Low Tone Horns Testing and Replacement
 
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Pelican Technical Article:

High and Low Tone Horns Testing and Replacement

Nick Czerula

Time:

1 hours1 hrs

Tab:

$10

Talent:

**

Tools:

10mm socket, trim panel tool, DVOM, test light

Applicable Models:

Mercedes-Benz W211 (2003-09)

Parts Required:

high and low tone horns

Hot Tip:

Be sure to properly position horns to prevent water intrusion

Performance Gain:

Working horns

Complementary Modification:

Replace horns in pairs

Mercedes-Benz W211 models are equipped with two horns, a high and low tone. A vehicle horn is a sound-making device used to warn others of the approach of the vehicle or of the vehicle's presence.

Mercedes-Benz W211 model horns are electric, driven by a flat circular steel diaphragm that has an electromagnet acting upon it, which is attached to a contactor that repeatedly interrupts the current to the electromagnet. This arrangement works like a buzzer. The horns produce sound levels around 107-109 decibels and have a current draw of 5-6 amperes. Mercedes-Benz W211 model horns are arranged in pairs, sounded together to produce two notes. The paired horns only increase the decibel output a small amount, but the two different notes are more perceptible, especially in an environment with a high ambient noise level.

The horn circuit on W211 models is complicated compared to models past. The horn button in the steering wheel is activated by the driver. That request for the horn is sent via CAN bus lines to the front SAM module, the SAM module activates the horn relay in turn activating the horns. For more specific info, see the end of this article for an overview of how to test the horns.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve, as they grow older. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

There is a high tone horn mounted on the right side of the radiator support (red arrow) and a low tone horn mounted behind the left side headlight, in the fender (blue arrow).
Figure 1

There is a high tone horn mounted on the right side of the radiator support (red arrow) and a low tone horn mounted behind the left side headlight, in the fender (blue arrow).

High tone: Open the engine hood.
Figure 2

High tone: Open the engine hood. Start by disconnecting the electrical connectors (red arrow). Pull the electrical connectors straight off the horn.

High tone: Then remove the 10mm horn fastener (red arrow).
Figure 3

High tone: Then remove the 10mm horn fastener (red arrow).

High tone: Once the fastener is removed, remove the horn from the vehicle.
Figure 4

High tone: Once the fastener is removed, remove the horn from the vehicle. When installing, be sure that the horn opening faces down. If you need to replace the horn mounting bracket (green arrow), remove the 10mm fastener (red arrow). Then remove and replace the bracket.

Low tone: Start by removing the front section of the left side wheel well liner.
Figure 5

Low tone: Start by removing the front section of the left side wheel well liner. See our tech article on wheel well liner removing. Disconnecting the electrical connectors (red arrows). Pull the electrical connectors straight off the horn.

Low tone: Then remove the 10mm horn fastener (red arrow).
Figure 6

Low tone: Then remove the 10mm horn fastener (red arrow). Note the position of the horn opening (green arrow) before removing. Be sure to install the new horn in the same position it was previously in. Remove the horn from the vehicle and replace it with the new one.

Horn testing: To test a horn, start by checking the horn fuses.
Figure 7

Horn testing: To test a horn, start by checking the horn fuses. Located in the left rear of the engine compartment (red arrow) is the front SAM. For my vehicle, fuses 53a and 53b are for the horn relay. Check that both of those fuses are OK. If both fuses are OK, remove the horn relay and jump terminals 30 and 87 together using a fused jumper wire. The horns should sound. If they do not, go to the horns to check if they are getting power.

Horn testing: Access the horn that is not working.
Figure 8

Horn testing: Access the horn that is not working. Then, disconnect the electrical connectors. Pull the electrical connectors straight off the horn. Connect a DVOM across the fuel pump terminals. These are the two horn terminals on my subject vehicle. The red arrow points to the battery positive feed to the horn. The green arrow points to the battery negative feed to the horn. Turn the key ON and press the horn button. When the horn button is pressed, you should have battery volts (yellow arrow) at the terminals, (about 12 volts). I suggest load testing using a test light and a DVOM. Connect the DVOM across the horn electrical connector terminals and take a reading. It should read battery volts when the horn button is pressed. Then connect an incandescent bulb style test light to battery ground and touch the test light probe tip to the positive wire you are backprobing with the DVOM. Your reading should hold steady. A maximum drop in voltage of 0.5 volts is OK. Anything more is a problem. In this photo, voltage held steady. If you have no voltage to the horn, the problem could be with the wiring, horn button, clock spring, relay, CAN bus or SAM module. If you suspect an issue with the CAN bus or steering wheel controls, your best bet is to test using a Mercedes-Benz scan tool. You can easily check for fault codes and activate the suspect components. If there is an electrical issue due to the CAN bus, steering wheel controls or the front SAM, a fault code will be stored. Usually, it's just a faulty horn, but keep these items in mind. One more note, the horns each have a ground located at the headlight assemblies on the side of the vehicle the horn is mounted to. Both horns share power from the relay. Two wires leave the front SAM going to each horn. If one horn has power and the other doesn't, this indicates a bad wire. You can locate the terminal at the SAM and replace the wire. Use a current wiring diagram for your vehicle to be sure you are on the right terminals. On my subject vehicle they are yellow wires coming out of pin 10 at connector M2.


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