The instrument cluster tachometer doesn’t function at all in my 54-plate smart roadster with 107,000 miles. The car is fitted with the optional extra trip computer which still shows the correct RPM, so I’m assuming the RPM signal/ sensor is functioning properly.
Unfortunately, I caused this problem by swapping the instrument cluster dial face from white to black, although the procedure went exactly as per the Evilution website instructions. The problem arose when I reattached the instrument cluster connection plug, as I unknowingly failed to seat and connect it properly. I then connected the battery and turned on the ignition, but nothing lit up on the cluster. I disconnected the battery and removed the instrument cluster, which was when the cable connection dropped out of its seating position. I refitted the cluster, making sure it was correctly connected, reattached the battery and turned on ignition. This time everything lit up, but the tachometer wasn’t working.
Is there any way of checking the cluster without creating more problems? I have inspected the cables leading to the cluster and noted some fusible links on some of the wires, but I’m not sure how to test them without disturbing the SAM unit below. I’m not sure how to check the cluster circuit for the tacho stepper motor, or if the tacho stepper motor can be replaced easily and what problems would arise if I tried to replace it.
I have managed to get hold of a secondhand instrument cluster – I’m unsure of its mileage and other settings stored in it – but I’m not too confident about fitting it as I have read that the mileage stored in the cluster EEPROM could overwrite the ECU/SAM mileage. I have also got the correct wiring diagram for the car, but I’m unsure what to look for as everything else is working fine on the cluster. I can only find one fuse in the SAM for the cluster and that is obviously OK.
Provided the plug to the tachometer wasn’t misaligned or inadvertently placed in the wrong position, it is unlikely that any damage should have occurred to the unit, given that you took adequate precautions by disconnecting the battery. However, it is possible that even though you believe the plug is now correctly located, a poor connection is still present. With this in mind, my first move would be to remove the plug again and spray the plug and connection with an electrical switch cleaner spray, then firmly reconnect the plug in the socket and check the operation of the tachometer.
As the second rev counter function is operating, you can discount the possibility that the tachometer circuit is at fault.
As you mentioned the website, I presume that you are a member of the site, in which case excellent instructions are available for cloning the ECU. From the details I have, the ECU will override the cluster and not the other way round.
Other problems that can occur include water damage to the SAM unit, but as everything was working before the disconnection, this is unlikely. One option may be to let a company such as this one check and, if required, repair the unit. Prices start at around £40, but as I've not personally used this company this is only a suggestions and not a recommendation.