Problem job: Mercedes 212 f32 fuse box design fault

Old f32 fault causes it to shut off without the command from rear SAM

Problem job: Mercedes 212 f32 fuse box design fault
Problem affects Mercedes 212, 207, 204 and 218 from production period 12/2011 to 03/2012.

Aftermarket vehicle diagnostics company, Autologic has revealed the fix for a common problem affecting Mercedes 212, 207, 204 and 218 from production period 12/2011 to 03/2012.

Location of the F32 under the bonnet.

A customer reported various symptoms affecting their Mercedes-Benz 212, including warning lights on in the instrument cluster.

Autologic say symptoms can vary depending on the model range of the vehicle.

A spokesperson said: “The warning lights could come on, some models might have various broken functions including the wiper washers, and for some models it can even result in the engine not being able to start, or not allowing you to select a gear.

“We have found that re-cycling the ignition may fix the issue temporarily.”

Fixing the fault

Carrying out a full vehicle scan will show most control units with numerous CAN communication faults including faults with ESP, engine, transmission, ignition switch, rear SAM, SRS, xenon headlights, multi function camera and parktronic.

Autologic say the common theme across all models are the codes in the rear SAM and SRS.

In the rear SAM you will have a few rear light codes, and the following:

  • A19600 (B219600) [Stored] the power supply of circuit 30g is < 7.5 V.
  • A19700 (B219700) [Stored] The power supply of circuit 30g is < 8.5 V.
  • A19116 (B219116) [Stored] The power supply of circuit 30g is outside the valid range. The limit value for electrical voltage has not been attained.
  • A14B72 (B214B72) [Stored] The output for switch ‘Quiescent current ON’ has a malfunction. The actuator does not close.

These codes indicate the premature closing of the 30G relay in the f32 fuse box – the jump point fuse box under the bonnet.

The other sign of this being the cause are the codes in SRS airbag:

  • A10F (B210F) [Stored] Event: Input ‘circuit 30’ has a malfunction.
  • 9C1A (B1C1A) [Stored] NECK-PRO head restraint ‘front passenger’ has an open circuit.
  • 9C14 (B1C14) [Stored] NECK-PRO head restraint ‘driver’ has an open circuit.

In all cases, these codes will be stored in the SRS module if the 30G feed is shut off prematurely.

The cause of the problem is a defective no-load current relay in the engine compartment pre-fuse box F32.

What is 30G?

30G is a 12 volt permanent live circuit which is shut down after six hours after vehicle is locked.

The result of which means that 60 per cent of control units receive a hard reset (power off and then on again at vehicle restart), this has the effect of less vehicle problems.

The rear SAM checks after 75 minutes and will find a drain of >50mA3 – it will then give a five-minute warning to the other control units to shut down.

After the other control units have shut down, it will then shut circuit 30G by triggering the shut off a control relay in F32 without waiting six hours.

If the voltages/quiescent current is within spec, the rear SAM will go back to sleep.

The system will always try to ensure the vehicle is able to start.

The battery sensor has a diagnostic facility to help diagnosis of current drain faults.

It’s important to disconnect the battery to replace the f32 fuse box but ensure the battery sensor is removed in the correct way to avoid further issues.

Disconnecting the battery

  • Unplug the electrical plug from the sensor (B95 red and blue wires) and unbolt the negative terminal.
  • To connect the new battery sensor, connect the negative terminal at 6nm and reconnect the electrical plug to the battery sensor clear codes. Electrical connection for B95 red +30 from battery positive blue/white LIN wire to rear SAM notes on jump starting/battery sensor maintenance operations.
  • When disconnecting the battery be aware that the wrong sequence can cause arcing and contact bounce. This will cause a LIN communication error, putting the battery sensor (B95) into a passive state and at this point it will stop sending information to rear SAM. ECO start stop will also stop working.
  • No steps are required for initial start-up of B95 battery control module.

Once the battery is correctly disconnected, the modified f32 fuse box can be replaced with a new part from Mercedes-Benz.

The old f32 has a design fault and will shut off without the command from rear SAM.

The battery will then be put back on line after the replacement

Clear codes as necessary and road test the vehicle on job completion.

For further information about Autologic, select ‘more details’ below.

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