BY Neil Currie This article is about a recent job I had that was very interesting indeed. I diagnosed the fault, but then the vehicle was taken to the dealership as we didn’t have the equipment required to finish the job. Of course, it ended up back at me with different symptoms. The vehicle in question was a Smart Roadster; Not your average common car often seen on the road. However, as we do all makes and models we would give it a shot and see what happens. Testing The vehicle was presented as a no crank with a flashing key symbol displayed on the dashboard. My first worry was that being a Smart, technical information would be in short supply. Luckily though, there was plenty available and the diagnostic scan tools listed the make and model so we were off to a good start. Verifying the customer complaint showed the ignition to come on with the flashing key symbol. However, when attempting to crank the engine nothing happened. Checking the key itself, it showed no output when tested for an RF signal output. Testing the battery within the key showed it to be flat so a new battery was fitted. However even with the key now outputting a signal the car did not respond and it still would not crank. I then scanned the entire vehicle and not many fault codes were stored. It was noted though that the front signal acquisition module (SAM) did not communicate. This is the Mercedes/Smart name for body control module. This 30 AFTERMARKET MARCH 2024 TECHNICAL www.aftermarketonline.net MAKING THE SMART CHOICES Top Technician 2019 champion Neil had a recent rebound job with a Smart Roadster that reinforced the importance of following a test plan unit is responsible for key data among the many other functions it carries out and would be the reason our car was immobilised. I then decided to access the module to carry out some tests to locate the fault and why we could not communicate. Referring to wiring diagrams, the power and ground wires were tested and found to be okay. When removing the connector to get pin numbers to verify I was on the correct plug to check the CAN BUS wires, there was small signs of corrosion on the pins pointing to a possible water ingress problem. Testing the CAN BUS signals with a scope showed textbook signals so the next step was to remove the SAM unit and get a better look at it. Inspecting Upon removing and inspecting it again, signs of corrosion were visible so this gave me enough evidence to split the plastic covers and inspect the circuit board itself and as we can see in Fig.1, this board had substantial water damage which had corroded the board. This now explains why we cannot communicate with it and have a no crank complaint. Pricing a new unit up from the dealer showed it to be over £500 and with this car being a 2004 model the cost of the repair posed the question of whether this was a viable repair compared to the value of the vehicle. There was an option to possibly clone the information from the old unit to a second-hand unit but with it being so badly damaged I felt it may not be possible to read the relevant chips on the board and a new unit was the best way to proceed.
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