Error code spn 647, fmi 5

Check with truckpro and Freightliner to compare prices, although Freightliner is usually pretty reasonable.

 

Yes, and if you have the prongs backwards it will just read negative voltage, but it will be correct voltage. Check the wires for any chafing or rubbing as far as you can follow them just to be safe. Get a multi meter with ac/dc and resistance reading values, it should have the OHM symbol. Those come in handy for reading sensor values.

 

Once you get a multi meter with resistance reading capability, you can dig a little deeper. The MCM is just the ECM which is bolted onto the block with two big harnesses attached. You would set your meter to read resistance, and unplug the harnesses and measure the resistance from the pins and the connector that plugs into the solenoid. It explains it in the link posted on the first page of this thread.

If certain values aren’t met, or are too high, most likely replace the solenoid. Or if they values are wrong, say lower than they should be, or higher too, you fix the wiring issue that caused it. That’s why I was saying to check all the wiring for chafing. Your problem is simple to fix, it just requires a little troubleshooting. Or you could just buy a new solenoid and see if that eliminates it before you start unplugging things.

If that is the only fault code showing, then it’s probably the solenoid.

 

is It the fuel temp sensor or fuel level sensor? If it’s the temp fault then it’s probably the sensor is dirty on the secondary fuel filter. If it’s the fuel level issue, that could be a loose connection behind the dash or at the tanks. Neither are really an issue, just more of an annoyance,

 

sometimes the computer has to do so many diagnostics checks before the code becomes inactive and disappears. I have had some do that on me. If the fan is changing speeds, then it should be back to normal. If it’s running full blast constantly a few days from now, check the resistance on the plug and harness and if it doesn’t meet the values, change the solenoid.