Usually the wrench indicator is saying it is time for the yearly or 10,000 mile service . 1 wrench means 10K, 2 wrenches means 20K When the wrench is on, the odometer will indicate how many miles (or days) until the service interval is due. If it shows a negative number, it is past due and either wasn't reset, or wasn't performed. If the wrenches are flashing, that is a whole different issue