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go-west.., Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 1132
Experience:  Technican with 20 years experience focused on engines and electrical.
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I have a 2008 Freightliner school bus with a intermittent

Customer Question

I have a 2008 Freightliner thomas school bus with a intermittent check engine light. The Incative codes are PID 45 FMI 12 Undifined, PID 158 FMI 1 Battery Voltage Switched, SID 248 FMI 2 Proprietary Data Link.
JA: We'll do all we can to help. Tell me a bit more about what's going on so the Heavy Truck Mechanic can help you best.
Customer: It does not have any drive ability concerns, the check engine light just comes on for a while then goes off. And all ican pull are these inactive codes.
JA: Is there anything else the Heavy Truck Mechanic should be aware of?
Customer: It has a Mercedes Diesel Engine
Submitted: 1 month ago.
Category: Medium and Heavy Trucks
Expert:  go-west.. replied 1 month ago.
Good morning,
the 45 code means there a problem with the grid heater, the 158 indicates low batter voltage
The 248 means the engine ecm and the cab ecm are not communicating..
Now I suspect that if you fix the charging issue it will fix everything else. Let me know if you have any other questions
Customer: replied 1 month ago.
Currently it is charging fine, and the light is intermittent. Is it possible a problem with the grid heater dropping battery voltage too low?
Expert:  go-west.. replied 1 month ago.
There was a recall on the grid heater. Has yours been checked?
I'm also thinking of week batteries. Are they older?
Customer: replied 1 month ago.
one of the batteries only has 150CCA
Expert:  go-west.. replied 1 month ago.
They should be 750 minimum
Customer: replied 1 month ago.
I put the new battery in, the check engine came on about 5 hours of driving later. Pid, 45 and 158 came back.
Expert:  go-west.. replied 1 month ago.
158 is that low voltage code
Start by checking the connections at the alt, starter. Make tight and clean
Expert:  go-west.. replied 1 month ago.
What is the voltage gauge reading when the light comes on?
Customer: replied 1 month ago.
Ill Check The Next Time It acts up, it is intermittent
Expert:  go-west.. replied 1 month ago.
Sounds good

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