Check function of relay - AR54.15-P-3000A

MODEL 140.051 /057 with CODE (979) special protection version 

Fig 1: Identifying Relay Function Component Location

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

	Checking
1	Remove hydraulic unit relay module (brake booster) (K37)	As of production 10/97 the hydraulic unit relay module (brake booster) (K37) is located in front of the engine compartment partition
	Risk of accident  due to vehicle starting off automatically when engine is running. Risk of injury  due to being trapped and sustaining burns when intervening during the starting operation or when the engine is running.	Secure vehicle to prevent it from starting off automatically. Wear close-fitting, tight clothing. Do not touch hot or rotating parts.	AS00.00-Z-0005-01A
2	Start engine
3	Operate brake pedal approx. 5 to 8 times until the low brake fluid level/parking brake indicator lamp illuminates	Engine pump unit must switch on at the same time as the low brake fluid level/parking brake indicator lamp illuminates
4	Do not operate brake pedal any more	The engine pump unit delivers for approx. 10 to 30 seconds until a brake pressure of approx. 140 bar is achieved. The low brake fluid/parking brake indicator lamp and the engine pump unit must switch off at the same time.
5	Switch off engine
6	Install hydraulic unit relay module (brake booster) (K37)
7	Remove hydraulic unit safety relay module (brake booster) (K37/1)
8	Start engine
9	Operate brake pedal approx. 3 to 5 times until the engine pump unit starts delivery
10	Do not operate brake pedal any more	The low level brake fluid/parking brake indicator lamp must not illuminate. Engine pump unit delivers for approx. 10 to 30 seconds until brake pressure of approx. 180 bar is achieved.
11	Switch off engine
12	Remove hydraulic unit relay module (brake booster) (K37)
13	Start engine
14	Operate brake pedal approx. 5 to 8 times until the low brake fluid/parking brake indicator light illuminates	Engine pump unit must not start.
15	Switch off engine
16	Install hydraulic unit relay module (brake booster) (K37) and Hydraulic unit safety relay module (brake booster) (K37/1)
17	Switch on ignition
18	Press button on low brake fluid level switch	Low brake fluid level/parking brake indicator lamp must illuminate.
19	Disconnect low brake fluid level switch intermediate connector (X88/4)	Do not pull off center part of low brake fluid level switch connector. Low brake fluid level/parking brake indicator lamp must illuminate.
20	Switch off ignition
21	Assemble brake fluid level switch internal connector (X88/4).