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Jeremy, Certified Truck/Bus Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 3382
Experience:  ASE Med/HD Truck Technician, NATEF Diesel Engines and Electrical/Electronics Technician, EPA 608/609 HVAC Certified, Steering/Suspension and ABS/Brakes Technician
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Hellev my name is eddie masson i have a frightliner in my

Customer Question

hellev my name is ***** ***** i have a frightliner in my shop with a ism cummins engine won,t start it will crank over starts with sarting fluid but won.tstay running.i change timming sensor,bromatic sensor,oil sensor,ecm,fuel pump,have power to the ecm,ran a hose from from pump to 5gl of fuel,and nothing any the only code it give me is 0434
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Jeremy replied 1 year ago.

My name is ***** ***** I will assist you.

Please don't forget to rate above. I'm an independent contractor that is oaid oer question. No rsting means site gets it all and zi get nothing. Same as negative rating.


Fault Code: 434
PID: S251
SPN: 627
FMI: 2
LAMP: Yellow

Supply voltage fell below (+) 6.2 VDC for a fraction of a second, or the electronic control module (ECM) was not allowed to power down correctly (retain battery voltage for 30 seconds after key-off).

The ECM receives constant voltage from the batteries through the unswitched battery wires that are connected directly to the positive (+) battery post. There are three in-line 7.5-amp fuses and one 20-amp fuse in the unswitched battery wires to protect the engine harness from overheating. The ECM receives switched battery input through the vehicle keyswitch wire, when the vehicle keyswitch is turned on

Make sure that ECM unswitched power is coming from the batteries and not the starter. Check for low voltage during cranking. Low voltage during cranking can cause the ECM power supply to drop below specifications and log Fault Code 434.

Corrupted voltage (short interruptions or spikes that may only be seen with an oscilloscope) on keyswitch line can cause this fault. If the voltage at pin 5 of engine connector is measured as negative with oscilloscope at key-off, Fault Code 434 can be logged.

A failure with the ECM can also cause this. Try a test ECM for the same vehiclenof you have one.

You can also shake the harness while you the vehicle is running to see if the vehicle shuts down.

Expert:  Jeremy replied 1 year ago.

Attached is the diagram to assist you with diagnosing the voltage issue.

Expert:  Jeremy replied 1 year ago.

I see you viewed this and this is still showing as a open question due to no positive (3 stars or more) rating.

Did you still need assistance with this?