New owner of a first 2004 AMG SL55 (V8 compressor engine), having intermittent problems starting car after it as been recently driven, and check engine light ODBC code indicating crankshaft sensor A error.
Engine cranks starter strong, but does not fire, looks like a fuel problem or ignition problem; if I leave the car sitting for about 20 minutes it will start right at first crank of starter motor, understanding now this is very likely an indication of bad crankshaft sensor.
Battery and charging circuit testing by my local friendly folks at O'Reilly auto parts and tested good, so certain not a battery issue.

Few questions please for people more experienced on these model cars.

1- understand from searching internet that the crankshaft sensor is on the driver side rear of engine block near the firewall towards the bell housing.
What is the preferred/easiest/best way to access it for replacement?
- Either from top of driver side fender and reach down between engine block and firewall and work pretty much in the blind, or
- remove driver front wheel and remove wheel cover and access it from below the driver fender?

2- I was told there are ODBC error codes for SENSOR A and for SENSOR B.... question is there a secondary crankshaft sensor on this 2004 AMG SL55, and if so where is it located please?
On internet I only see general references to one sensor located at driver side at rear of engine near the bell housing.

3- Do I need to disconnect the car battery in engine compartment before unplugging and reconnecting cable to sensor, or the auxiliary battery in the trunk area, or is it safe to disconnect/connect wire with both batteries connected?
This engine start problem and check engine light problem started after I removed a blown 30 amp cigarette lighter fuse in engine compartment fuse box and inserted a new one.... not sure if that was the start of damaging the sensor or just coincidence.....

Thank you for any advice to help me correct this problem.
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