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Pelican Technical Article:

Clockspring Removal

Tom Morr

Time:

2 hours2 hrs

Tab:

$115 to $140

Talent:

**

Tools:

Long T30 Torx driver, 10mm hex, Allen bit, socket extensions, breaker bar, Phillips screwdriver, small flathead screwdriver

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

airbag clock spring assembly.

Hot Tip:

Zip-tie the assembly together until ready to screw it in place.

Performance Gain:

Restores correct sensor, warning light function.

Complementary Modification:

Replace the steering wheel

Mercedes-Benz often separates its various sensors into stand-alone/single-purpose units. One example is the steering-angle position sensor, which plugs into the airbag clock spring/horn contact ring on many cars.

The R170 SLK is one Mercedes-Benz model that integrates these sensors into a single assembly. What looks like "plugs" on the assembly's housing are actually single-piece boots. The assembly's halves come apart, but its plugs actually connect at the terminal block near the fuse panel. The bad news is that malfunctions in the airbag, steering, and/or "fanfare signal system" (jargon for "horn") can require replacing the assembly.

You will need to remove the steering wheel and lower interior panel first. Please see our articles on Steering Wheel Removal and Lower Interior Panel Removal for details on these preliminary steps.

If the ESP warning light comes on after all the parts are installed and the battery is reconnected, the steering-angle sensor might need to be calibrated. This is accomplished by steering the car lock-to-lock with the engine idling.

An airbag misfire can be deadly.
Figure 1

An airbag misfire can be deadly. When disconnecting the battery to disable the airbag, make sure that the negative cable and battery post are separated and shielded. Then wait about 30 minutes for the airbag's capacitor to discharge.

A T30 Torx driver, ideally 2.
Figure 2

A T30 Torx driver, ideally 2.5 inches or longer, is required for removing the airbag bolts from the steering wheel's backside. Wiggle the Torx bit in the steering wheel holes (at the 3:00 and 9:00 positions on the wheel) until it seats in the bolts' heads.

Unplug the airbag (green arrow) and store it out of the sun, airbag side facing up.
Figure 3

Unplug the airbag (green arrow) and store it out of the sun, airbag side facing up.

Once the airbag is removed, the steering wheel's retaining screw is accessible.
Figure 4

Once the airbag is removed, the steering wheel's retaining screw is accessible. The steering wheel must be stabilized so that the force required to loosen the screw doesn't damage the steering wheel's locking mechanism.

The clock spring assembly is secured by and oriented with two Phillips screws (green arrows).
Figure 5

The clock spring assembly is secured by and oriented with two Phillips screws (green arrows). The unit installs with the wires on the right side to ensure proper airbag and ESP function.

On some Mercedes-Benz models, the steering angle sensor plugs into the rear of the clock spring assembly.
Figure 6

On some Mercedes-Benz models, the steering angle sensor plugs into the rear of the clock spring assembly. In the R170 SLK, the gray pieces (green arrows) look like plugs but are actually boots that protect the transitions from wires to the ribbon cable inside the clock spring.

If the existing assembly is being retained, consider zip-tying the halves together and leaving the Phillips screws in the housing.
Figure 7

If the existing assembly is being retained, consider zip-tying the halves together and leaving the Phillips screws in the housing. The halves snap apart easily, and the ribbon cable inside can un-spiral, causing incorrect airbag signals.

With the lower interior panels removed, the assembly's pigtails can be carefully freed from its tie-downs.
Figure 8

With the lower interior panels removed, the assembly's pigtails can be carefully freed from its tie-downs.

The pigtails connect at the terminal block, located next to the interior fuse panel.
Figure 9

The pigtails connect at the terminal block, located next to the interior fuse panel. One plug mounts in the block's "D" slot. It slides out of the slot.

A small flathead screwdriver helps release the plug's tang.
Figure 10

A small flathead screwdriver helps release the plug's tang.

The sensor assembly's red plug clips into the terminal block.
Figure 12

The sensor assembly's red plug clips into the terminal block. The flathead helps push it out of the block.

The assembly removes by fishing its harness through the steering column's collar.
Figure 13

The assembly removes by fishing its harness through the steering column's collar. Adequate plug clearance is created by removing the cruise control stalk (green arrow), which is held in place by one Phillips screw.

In the R170, a single assembly (170-460-01-49-MBZ) senses the steering angle, airbag position, and horn contact status.
Figure 14

In the R170, a single assembly (170-460-01-49-MBZ) senses the steering angle, airbag position, and horn contact status.

The assembly's two halves press apart with finger pressure.
Figure 15

The assembly's two halves press apart with finger pressure. If the clock spring's ribbon cable un-spirals, it can be rewound. With the halves back together, adjust the clock spring by rotating the top half counter-clockwise until slight resistance is felt. Then back it off clockwise 2-2.5 turns. Installation is the reverse of removal. If the ESP warning light comes on after all the parts are installed and the battery is reconnected, the steering-angle sensor might need to be calibrated. This is accomplished by steering the car lock-to-lock with the engine idling.

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Comments and Suggestions:
Rick Comments: Excellent details, Nick. Question on a 1999 R170. Horns aren't working. Checked each horn - work fine when wired to 12V. Both fuses are fine and horn relay on the K40 is fine. Wiring in the engine compartment looks fine. Leads me to the clockspring, but I don't have the common ABS light on when it fails. Is there anyway to test to see if the horn signal is made by the clockspring?
September 17, 2016
  Followup from the Pelican Staff: Yes. You can locate the connector for the horn after the clock spring. Press the horn, does the horn signal change? Should be grounded. - Nick at Pelican Parts  
Rubi Comments: Hi Nick, I mean that the whole article is titled Steering Angle Sensor removal but you show how to remove the Clockspring. Best regards
June 18, 2016
  Followup from the Pelican Staff: AHHh, gotcha. I will have the title adjusted. - Nick at Pelican Parts  
Rubi Comments: Hi,
Sorry but it is not clear to me where the steering angle sensor is. What appears on the Figure 15 photo is the clock spring, this is just an spiral wire with 4 channels, 2 for airbag and 2 for the horn. Is it right? I was expecting some sort of electronic encoder as the steering sensor.

Thanks
June 8, 2016
  Followup from the Pelican Staff: The possibility of steering wheel position changing could set a steering angle fault. That may be why it is mentioned. - Nick at Pelican Parts  

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