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Mercedes Benz Electronic Ignition System (EIS) Diagnosis

How to diagnose a no crank condition caused by a faulty Electronic Ignition System (EIS)

In this video and article, how to diagnose a no crank condition caused by a faulty Electronic Ignition System (EIS) will be shown. A no crank, no start fault is shown along with the multiple cause with diagnosis.

Begin by identifying the vehicle you are working on

Select Body

Select Electronic Ignition System (EIS)

Select Actual Values

Select Terminal 15 Terminal 50

EIS Remote Key and Terminal Data Will be displayed

With the key in the ON position

Key in “HO” (auxiliary contact) should display YES

Output for circuit 15r should display ON (add key turning picture in picture)

Output for circuit 15 should display ON

Output for circuit 50 should display OFF

Attempt to crank engine

Output for circuit 50 should change from OFF to ON

 

 

If it does not switch, the issue may be the Drive Authorization, System (DAS) not allowing the start signal. Attempt to start vehicle using a second known good key. If change still does not occur, engine start may be blocked by implausible park signal or no communication to / from a DAS module, (Transmission, Engine, Shifter, Bad Key). Further diagnosis is needed

If circuit 50 does change from OFF to ON and the starter does not crank, the issue may be the starter motor or the passenger side SAM

Working at the right side of the engine compartment, unclip and remove the electronic box cover

Using a wiring diagram, locate the connector for the output to starter for circuit 50

Insert a backprobe into terminal 50. Connect your DVOM negative lead to battery negative and the positive lead to the backprobe at circuit 50

Have an assistant crank the engine while monitoring voltage on DVOM

When cranking, voltage should change from close to zero volts to battery positive volts. As shown. The test light illuminating indicates the circuit is able to hold a load

 

 

If meter voltage does not change from close to zero volts to battery positive volts, the passenger side SAM module is may be at fault. Consult a Wiring diagram and check for proper power and ground to the SAM before condemning it

If voltage is present and engine does not crank, the starter is likely faulty. Test circuit 50 at starter solenoid and confirm negative and positive connections at starter do not have excessive voltage drop