Onan 7500 fault code 38
- Thread starter dirtdog
- Start date
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Gary RV_Wizard
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A 38 is a general overload fault. It could be simply too many amps drawn by external applainces, but usually one of the genset breakers trips first. Other causes are possible. It's still too many amps, but the reason it is "too many" is that some other problem causes the overload condition to occur. Onan says this in the QD 7500 service manual:
Corrective Action:
1. Reduce the number of appliances running at the same time, especially those with high motor starting
loads such as air conditioners. Start up with no load and let the genset run for five minutes to cool
down the inverter.
2. If the appliance and air conditioner loading patterns have remained the same but genset performance
has deteriorated:
A. Check for fuel and air leaks at each fitting in the fuel supply line. (Note: White smoke indicates
air in the fuel.)
B. Conduct a fuel flow test and service as necessary (p. 14-1).
C. Remove the front and top housing panels (p. 6-4). Check for binding in the governor mechanism
by pushing the actuator rotor clockwise by hand?against the action of the fuel rack return
spring. It should rotate smoothly about 1/2 inch (12 mm) and return smoothly. If it binds or
catches, remove the governor actuator base assembly and replace it or service the internal engine
governor mechanism (p. 13-3) as necessary.
D. Readjust high-idle speed (p. 13-4).
E. Service the fuel injectors and injection pump as necessary (p. 12-1).
F. Service a worn engine (p. 12-1).
As you can see, some of the causes are obscure, like a faulty governor. The genset doesn't respond quickly enough to load changes and it overloads. For example, you may not realize that the genset died just as an a/c tried to start, so miss the important clue. A well-trained tech can do measurements on all that stuff, but few do it because diagnostic labor costs may well exceed the price of throwing parts at it, and you still have to buy at least one part anyway. If you have the skills to check that stuff yourself, that's a different story.
You can find the service manual online for free.
Corrective Action:
1. Reduce the number of appliances running at the same time, especially those with high motor starting
loads such as air conditioners. Start up with no load and let the genset run for five minutes to cool
down the inverter.
2. If the appliance and air conditioner loading patterns have remained the same but genset performance
has deteriorated:
A. Check for fuel and air leaks at each fitting in the fuel supply line. (Note: White smoke indicates
air in the fuel.)
B. Conduct a fuel flow test and service as necessary (p. 14-1).
C. Remove the front and top housing panels (p. 6-4). Check for binding in the governor mechanism
by pushing the actuator rotor clockwise by hand?against the action of the fuel rack return
spring. It should rotate smoothly about 1/2 inch (12 mm) and return smoothly. If it binds or
catches, remove the governor actuator base assembly and replace it or service the internal engine
governor mechanism (p. 13-3) as necessary.
D. Readjust high-idle speed (p. 13-4).
E. Service the fuel injectors and injection pump as necessary (p. 12-1).
F. Service a worn engine (p. 12-1).
As you can see, some of the causes are obscure, like a faulty governor. The genset doesn't respond quickly enough to load changes and it overloads. For example, you may not realize that the genset died just as an a/c tried to start, so miss the important clue. A well-trained tech can do measurements on all that stuff, but few do it because diagnostic labor costs may well exceed the price of throwing parts at it, and you still have to buy at least one part anyway. If you have the skills to check that stuff yourself, that's a different story.
You can find the service manual online for free.
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