Mercedes-Benz W212 E400 Front SAM Fuse and Relay Guide

FRONT SAM (Signal Acquisition Module) Overview

The Front SAM is a critical component in the vehicle's electrical system, managing various functions through fuses and relays. This document details the identification and function of these components.

Diagram of Front SAM Layout:

The Front SAM unit is depicted with numbered positions for relays, labeled from 1 to 36. Key positions include:

• J, K, P: Associated with Circuit 15 relay.
• L, N: Associated with Circuit 87 relay.
• M: Associated with Starter circuit 50 relay.
• Q: Associated with Transmission oil auxiliary pump relay.
• O, R: Associated with Horn relay and Chassis circuit 87 relay.

Circuit and Power Line Descriptions

Understanding the circuit designations is crucial:

• 30: Continuous positive power, not switched by relay or switch.
• 30g: Switched positive, fused, often from the PreFuse Block.
• 30z: A unique Circuit 30, often for the ECM Engine Computer.
• 31: Return line to battery negative or ground.
• 50: Circuit to the starter solenoid.
• 15: Switched circuit, powered by a relay.
• 15R: Switched circuit, often with a double relay setup.
• 87F: Circuit often related to transmission or fuel control.
• 87M: Circuit typically dedicated to engine operation.

Fuse and Relay Functions

The following details specific fuses and their functions:

Fuse 1: 25 Amps

Power Source: 30. Function: HVAC Blower Fan (A32n1) for Left Hand Drive cars. In this Right Hand Drive vehicle, the HVAC blower receives power from F32 FuseBlock.

Fuse 2: 30 Amps

Power Source: 30. Function: Supposedly for Left Rear Door Control Unit (N69/3) up to 2010. For this vehicle, it is for the Front Right Door Control Unit (N69/2).

Symptoms of blown fuse: Instrument cluster warnings (EDB, ABS, ESP), loss of power windows, driver's seat adjustment, and rear-view mirror adjustment. Trouble codes related to the right front door module (N69/2) and other door modules.

Fuse 3: 30 Amps

Power Source: 30. Function: Supposedly for Right Front Door Control Unit (N69/2) up to 2010. For this vehicle, it is for the Left Rear Door Control Unit (N69/3).

Symptoms of blown fuse: Similar to Fuse 2, affecting power windows and door locks.

Fuse 4: 20 Amps

Power Source: 15 (from Relay J). Function: UNUSED in this vehicle. For Diesel or M157 engines only.

Fuse 5: 7.5 Amps

Power Source: 15 (from Relay J). Function: Power feed to Rear SAM 10/2. A blown fuse may cause an unreasonable Circuit 15 signal.

Fuse 6: 10 Amps

Power Source: 15 (from Relay J). Function: UNUSED in this vehicle. For Diesel or Natural Gas engines only.

Fuse 7: 20 Amps

Power Source: 15 (from Relay J). Function: Power source for pin 30 of Relay M (starter circuit 50/solenoid). A blown fuse or a faulty Relay M can prevent the engine from cranking.

Fuse 8: 7.5 Amps

Power Source: 15R (from Relay K). Function: Supplemental Restraint System (SRS) or airbags & seat belts. A blown fuse will trigger a "Restraint sys malfunction" warning.

Fuse 15: 7.5 Amps

Power Source: 30g. Function: Also supplies the SRS module (N2/10), acting as a secondary power source.

Fuse 9: 15 Amps

Power Source: 15R (from Relay K). Function: Supposedly for the glove compartment socket (X58/31). UNUSED in this vehicle.

Fuse 10: 30 Amps

Power Source: 15R (from Relay K). Function: Wiper motor (M6/1). A blown fuse will cause wiper malfunction.

Fuse 11: 7.5 Amps

Power Source: 30g. Function: Supplies the Audio Command 5” display. Music playback may continue, but the display will shut off.

Fuse 12: 7.5 Amps

Power Source: 30g. Function: HVAC control panel (N22/7), Upper Control Panel (N72/1) for parking lights, and Automatic transmission mode button (S16/12). A blown fuse will disable these functions without a warning.

Fuse 13: 7.5 Amps

Power Source: 30g. Function: Steering column tube module control unit (N80). A blown fuse can lead to various issues including transmission not engaging, non-functional wipers, horn, multimedia buttons, and steering column adjustments.

Fuse 14: 7.5 Amps

Power Source: 30g. Function: Electronic Stability Program control unit (N30/4). A blown fuse will result in "Run Flat Indicator Inoperative" and traction system malfunctions.

Fuse 15: 7.5 Amps

Power Source: 30g. Function: Supplemental restraint system control unit (N2/10). A blown fuse will display a "Restraint sys malfunction" warning.

Fuse 16: 5 Amps

Power Source: 30g. Function: UNUSED in this vehicle.

Fuse 17: 30 Amps

Power Source: 30g. Function: Panoramic sliding roof control module (A98). A blown fuse will stop the panoramic roof from working.

Fuse 18: 7.5 Amps

Power Source: 30. Function: Upper control panel control unit (N72/1) including Hazard Light switch, and the coil for the Transmission oil auxiliary pump relay (N10/1kQ).

Fuse 19: 20 Amps

Power Source: 30. Function: UNUSED in this vehicle. Related to 722.9 transmission and steering lock.

Fuse 20: 40 Amps

Power Source: 30. Function: UNUSED in this vehicle. Supposedly for ESP on Left Hand Drive cars.

Fuse 21: 7.5 Amps

Power Source: 15R (from Relay K). Function: Brake Light Switch S9/1 and Glove compartment lamp E13/1.

Fuse 22: 15 Amps

Power Source: 87M. Function: ECM N3/10 and Cooling Fan. Also powers oxygen sensor heaters and the engine oil pump valve.

Fuse 23: 20 Amps

Power Source: 87M. Function: ECM N3/10, including Ignition Coils and Camshaft sensors for Bank 1.

Fuse 24: 15 Amps

Power Source: 87M. Function: ECM N3/10, including Ignition Coils and Camshaft sensors for Bank 2.

Fuse 25: 15 Amps

Power Source: 87M. Function: ECM N3/10. May affect sensors and low power components.

Fuse 26: 20 Amps

Power Source: 30g. Function: Code 510 Audio CD with 6 disk changer. A blown fuse will disable the audio system.

Fuse 27: 7.5 Amps

Power Source: 30z (direct from F32 PreFuse Box). Function: ECM N3/10. A blown fuse will cause total loss of DC power, rendering the ignition and instrument cluster inoperative.

Relay Functions

Relay J (Circuit 15 relay)

Function: Provides power to Circuit 15. A failure in Relay J can lead to power loss for several circuits, including those powered by fuses 5, 6, 7, 29, 30, and 33, and can affect the operation of relays R and M.

Relay R (Chassis circuit 87F)

Function: Powers Circuit 87F. Its coil is powered by Relay J. Failure affects fuses 33, 35, and 36.

Relay N (Circuit 87M)

Function: Powers Circuit 87M, which feeds various ECM components and sensors via fuses 22, 23, 24, and 25. Its coil is commanded by the ECM.

Relay K (Circuit 15R)

Function: Powers Circuit 15R, which feeds fuses 8, 9, 10, and 21.

Relay L

Function: Related to Wiper Park Position Heater and Wiper Motor.

Relay O

Function: Powers horns (H2 & H2/1) via fuse 31B.

Relay P

Function: Related to the auxiliary transmission oil pump (N89) and secondary air injection (M272 engine).

Relay Q

Function: Powers the auxiliary transmission oil pump (N10/1kQ).

Relay M

Function: Starter circuit 50 relay.

F32 PREFUSE Box

The F32 Prefuse box provides main power distribution:

• MR8 (F150, 350 amps): Alternator output to protect the battery.
• MR6 (F153, 60 amps): Power feed for Fuse 27 (ECM N3/10).
• MRG2 (F156, 150 amps): Power to Circuit 30g of Front SAM (N10/1).
• IG1 (F158, 150 amps): Power to Circuit 30g of Rear SAM (N10/2).
• MR3 (F157, 80 amps): Main power for Electric Power Steering (N68).
• Pin 2 (F162, 60 amps): Power to ESP - Electronic Stability Program Control Unit (N30/4).
• MR4 (F151, 100 amps): Power for M4/7 radiator cooling fan.
• MR6 (F153, 60 amps): Power to Circuit 30z of Front SAM (N10/1).
• MR7 (F154, 150 amps): Power to Circuit 30 of Front SAM (N10/1).

Note on K2 Relay: If the K2 relay fails, all Circuit 30g circuits in the front and rear SAM will lose power. The K2 relay's timeout can be up to 2 hours after key removal, so testing for parasitic draw requires attention to this delay.