Onan Generator How to & Troubleshooting Guide

A comprehensive guide to help you troubleshoot your generator is a must-have whether you are a new generator owner or not. This article provides all the information you need to maintain and fix your Onan generator.  

Onan generator runs but has no power

The most common cause of portable generators failing to produce electricity is the loss of residual magnetism. Generators work by moving electrical conductors through a magnetic field, which is created by taking some of the generator output voltage and converting it to DC and feeding it to a coil to make an electromagnet. 

The leftover magnetism from the last time the generator was running is called residual magnetism. The residual magnetism is enough to produce a small amount of electricity which creates a stronger electromagnet. As the generator engine turns, this magnet produces even more power. When the residual magnetism is lost, the generator will produce no power at the start-up.  

The leading causes of magnetism loss include;

  • Prolonged disuse of generator.
  • Connecting the load to the generator when it is not running.
  • Running the generator with no load for too long. 

How to resolve the magnetism issue

These are two main methods for restoring a generator’s residual magnetism;

12 Volt Generator Battery Method

  • Locate the voltage regulator for your generator.
  • Unplug the two wires that connect to the generator brushes. Usually, one is red, and the other is black or white.
  • Connect the black or white to the generator ground battery terminal.
  • Plug in a light, turn on the generator breaker or switch and start the motor.
  • Connect the battery +12 volts red cable to the red wire on the terminals you removed for three seconds.
  • Remove your wires and replace the plug. The generator should now be producing power again.
  • Make sure you unplug the brush wires from the automatic voltage regulator, or you will damage the regulator.
  • Do not contact the voltage regulator or other wires as dangerous voltages may be present that can cause electric shock.

Electric Drill Method

  • Plug in an electric drill into the generator receptacle.
  • If the drill is reversible, move the direction switch to the forward position.
  • Start the generator while depressing the trigger on the drill.
  • Spin the drill chuck in the reverse direction. This will excite the field, and the generator will now produce electricity.
  • If turning the chuck in one direction does not work, try spinning the chuck in the other direction as you may have the reverse switch positioned backwards.
  • Use caution not to get your hand or other materials caught in the chuck. As soon as the magnetic field is exited, the generator will produce power, and the drill will turn on.

Note: If these methods do not help you restore generator output power, replace the Automatic Voltage Regulator as it may be damaged.

How do I read codes on Onan generator?

Onan generators use a blink and pause design to signal the error code. The two-digit code consists of 1, 2, 3, 4 or 5 blinks, a brief pause, and then 1 to 9 blinks. The first blinks represent the tens digit, and the second blink indicates the unit’s digit of the fault code number. For example, Fault Code No. 36 appears as:

blink-blink-blink—pause—blink-blink-blink-blink-blink-blink— long pause—repeat.

If the light blinks five times, then pauses, then flashes one more time, that signifies Fault Code 51.

All Onan generator troubleshooting codes, their meaning and fixes

The generator’s controller provides extensive diagnostics by causing the status indicator light on the Control Switch to blink in a coded fashion. After a Fault shutdown, the indicator light will repeatedly blink 2, 3 or 4 blinks at a time.

  • Two blinks indicate a low oil pressure fault.
  • Three blinks indicate a service fault. Press Stop once to cause the two-digit, second-level fault code to blink. Pressing Stop again will stop the blinking.
  • Four blinks indicate that cranking exceeded 30 seconds without the engine starting.

Note: Fault Code Nos. 3 and 4 are first-level faults. Avoid interpreting them as second-level Fault Code Nos. 33 and 44, which have not been assigned as fault codes.

Status indicator light dead

Faulty connections, no battery voltage

  • Try the generator Start Switch if the remote Start Switch does not work, and vice versa.
  • Clean and tighten the positive + and negative – battery cable connections at the battery, vehicle frame and generator.
  • Recharge or replace the battery. Refer to the battery manufacturer’s recommendations.

Starting batteries run down

Marginal batteries, connections, or charging system or parasitic loads

Corrective Action:

  • Clean and tighten the positive + and negative – battery cable connections at the battery, vehicle frame and generator.
  • Recharge or replace the battery. Refer to the battery manufacturer’s recommendations.
  • Have a battery charging system installed or serviced in the vehicle.

Starter engages-disengages

Cranking voltage dips below 6 volts—low battery charge, poor connections, long cables

Corrective Action:

  • Have the vehicle propulsion engine running while trying to start the generator. The battery charging alternator may be able to maintain starting voltage high enough to get the generator started.
  • Clean and tighten the positive + and negative – battery cable connections at the battery, vehicle frame and generator.
  • Recharge or replace the battery. Refer to the battery manufacturer’s recommendations.
  • Increase battery cable size or run parallel cables.

No power—generator running, the status light on

Line circuit breaker OFF, or tripped due to short circuit or overload

Corrective Action:

  • Turn on or reset the line circuit breaker on the generator
  • Turn on or reset the line circuit breakers on the main distribution panel in the vehicle.

Code No. 2: Low Oil Pressure Fault

First-level fault code—Low oil pressure cutoff switch did not open

Corrective Action:

  • Check engine oil level and add oil as necessary.
  • Drain excess oil above dipstick Full mark.

Code No. 3: Service Check Fault

First-level fault code—Indicates fault with second-level fault code

Corrective Action: Check the second-level fault code by pressing STOP once. The second-level fault code will have two digits. The faults are listed in numerical order in this table.

Code No. 4: Overcrank Fault

First-level fault code—Cranking exceeded 30 seconds without engine starting

Corrective Action:

  • Gasoline Models – Check and fill the fuel tank as necessary.
  • Prime the engine fuel system by holding the control switch at Stop/Prime for 30 seconds.
  • Low-Pressure LPG Models – Check and fill the LPG container as necessary.
  • The LPG container may have to be kept at least half full-on cold days to provide the vaporization rate required to keep up with the generator fuel demand.
  • High-Pressure LPG Models – Check and fill the LPG container, as necessary, and drain the generator LPG system of oil that may have migrated from the supply system.
  • Make sure to re-close the drain valve.
  • Open any closed fuel valves.
  • Secure the spark plug leads on the spark plugs.
  • Replace the spark plugs.
  • Service the air cleaner.

Code No. 12: Overvoltage Fault

Controller unable to maintain rated voltage

Corrective Action: See an authorized Onan dealer.

Code No. 13: Undervoltage Fault

Controller unable to maintain rated voltage

Corrective Action: Reduce the number of connected appliances, especially when air conditioners and battery chargers run.

Code No. 14: Overfrequency Fault

Engine governor unable to maintain rated frequency

Corrective Action: See an authorized Onan dealer.

Code No. 15: Underfrequency Fault

Engine governor unable to maintain rated frequency

Corrective Action:

  • Reduce the number of connected appliances, especially when air conditioners and battery chargers are running.
  • High-Pressure LPG Models – Drain the generator LPG system of oil that may have migrated from the supply system. Make sure to re-close the drain valve.

Code No. 19: Governor Actuator Fault

Controller sensed open or shorted circuit

Corrective Action: See an authorized Onan dealer.

Code No. 22: Governor Actuator Overload Fault

Duration of operation at or near full-duty cycle beyond the design limit

Corrective Action:

  • Reduce the number of connected appliances, especially when air conditioners and battery chargers are running.
  • Service the air cleaner.
  • Check for and repair a blocked exhaust system.

Code No. 23: Low Oil Pressure Cutoff Switch Fault

Controller sensed switch still open during start—not a running fault

Corrective Action: See an authorized Onan dealer.

Code No. 27: Voltage Sense Fault

Controller unable to sense the output voltage

Corrective Action: See an authorized Onan dealer.

Code No. 29: High Battery Voltage Fault

The voltage across the battery system is more significant than 19 volts

Corrective Action:

  • Check battery bank connections and reconnect if necessary so that the 12-volt batteries serving the generator are connected in parallel 12 volt rather than in series 24 volt.
  • Select a lower battery boost charge rate.

Code No. 31: Overspeed Fault

Engine speed more fabulous than 3400 rpm

Corrective Action: See an authorized Onan dealer.

Code No. 32: Low Cranking Speed Fault

Cranking speed less than 180 rpm for more than 2 seconds

Corrective Action:

  • Clean and tighten the positive + and negative – battery cable connections at the battery and the generator.
  • Recharge or replace the battery. Refer to the battery manufacturer’s recommendations.
  • Replace engine oil with oil of proper viscosity for ambient temperatures. High oil viscosity can slow down cranking speed.

Code No. 35: Control card failure fault

Microprocessor EEPROM error during self-test

Corrective Action: See an authorized Onan dealer.

Code No. 36: Engine stopped fault

Engine stopped without command by the controller

Corrective Action:

  • Gasoline Models – Check and fill the fuel tank as necessary. Note: The generator fuel pickup tube is probably higher in the fuel tank than the vehicle engine pickup.
  • Low-Pressure LPG Models – Check and fill the LPG container as necessary. The LPG container may have to be kept at least half full-on cold days to provide the vaporization rate required to keep up with the generator fuel demand.
  • High-Pressure LPG Models – Check and fill the LPG container, as necessary, and drain the generator LPG system of oil that may have migrated from the supply system. Make sure to re-close the drain valve.
  • Secure the spark plug leads on the spark plugs.
  • Replace the spark plugs.
  • Service the air cleaner.
  • Check for mechanical damage.

Code No. 37: Invalid generator configuration fault

Wrong frequency/rpm ratio

Corrective Action: See an authorized Onan dealer.

Code No. 38: Overcurrent field overload fault

Low power factor loads

Corrective Action:

  • Reduce the number of appliances running simultaneously, especially those with high motor starting loads such as air conditioners.
  • Check your air conditioners and other appliances to see if they are working correctly. For example, a locked compressor rotor can cause a low power factor.

Code No. 41: Generator Rotor Fault

Controller unable to sense field or output voltage

Corrective Action: See an authorized Onan dealer.

Code No. 42: Processor Fault

Microprocessor ROM error during self-test

Corrective Action: See an authorized Onan dealer.

Code No. 43: Processor Fault

Microprocessor RAM error during self-test

Corrective Action: See an authorized Onan dealer.

Code No. 45: Speed Sense Fault

Controller unable to sense quadrature frequency

Corrective Action: See an authorized Onan dealer.

Code No. 47: Ignition Fault

Controller unable to sense ignition

Corrective Action: See an authorized Onan dealer.

Code No. 48: Generator Field Sense Fault

Controller unable to sense field voltage

Corrective Action: See an authorized Onan dealer.

Code No. 51: Processor Fault

Microprocessor malfunction

Corrective Action: See an authorized Onan dealer.

Code No. 52: Fuel Injector Fault

Open or short circuit in fuel injector

Corrective Action: See an authorized Onan dealer.

Code No. 54: Mat Sender Fault

Open or short circuit in MAT sender

Corrective Action: See an authorized Onan dealer.

Code No. 56: Map Sender Fault

Open or short circuit in MAP sender

Corrective Action: See an authorized Onan dealer.

Code No. 57: Overprime Fault

Prime mode exceeded 3 minutes

Corrective Action: Check for and remove any object holding either control switch remote or local in the prime position.

How to clear codes on Onan generator

Follow these steps to clear a fault code on Onan generator;

  • Locate the primer button on the generator.
  • Hold the primer button down for at least 30 seconds.
  • Release the button and start the generator.
  • Allow the generator to run for 15 minutes to ensure that the code has cleared.

How to change the air filter on the Onan generator

The air filter traps dust and impurities in the air when clean air is drawn into the cylinder to prevent the wear and tear of the piston connecting the rod group, valve mechanism, and cylinder.

A blocked air filter will lead to smoke generation due to reduced air supply. First, inspect the air resistance indicator installed on the intake pipe behind the air filter to check if the filter is blocked.

If the air resistance indicator window changes from green to red under normal conditions, the filter is to be cleaned or replaced.

Follow these steps to replace the air filter;

  • Tap the air filter end cap to shake the dust accumulated on the filter.
  • Open the dust outlet of the dust disk and let go of the accumulated dust.
  • Open the filter end cap and pull the filter core out.
  • Block both ends of the filter element with a clean cloth or rubber stopper, and then use the dry compressed air with a pressure of not more than 0.2~0.3Mpa to blow the filter core surface in the direction of the filter core or outward from the filter element.

Note: It is not allowed to clean the air filter element with oil or water. It can be cleaned with hot alkaline water and or compressed air. The inner filter element of the heavy-duty air filter cannot be cleaned. And lastly, the swirl tube is fixed with its casing and is not removable.

How to replace the filter element

  • Loosen the wing nut that fastens the bottom cover to the filter housing and remove the filter cover.
  • Pull the filter element down from the centre bolt.
  • Remove the sealing gasket from the outlet end of the filter.

Note: When installing the filter element, make sure that the filter element is located on the gasket at the outlet end of the air filter.

Signs it is time to replace the air filter?

  • The air filter element is  damaged
  • The intake resistance indicator indicates is red.
  • You have already cleaned the filter core more than five times

How to change the oil in an Onan generator

To maintain your generator, you should run it at least once a month to circulate the oil. Additionally, you should endeavor to change the oil at least once per year or after 100 hours of use.  

Follow these steps to change the oil in your generator;

  • Run the generator for a few minutes to warm it up before you drain the oil
  • Shut down the generator
  • Using T-30 Torx bit/socket, remove the green panel on the underside of the generator that covers the drain plug see photo. Note: You only need to remove one screw then loosen the other. Then just swing the panel off to the side.
  • Using the 9/16 socket, remove the drain plug
  • Drain the oil into your oil pan until all of the oil is drained
  • Apply some pipe thread sealant to the drain plug and screw it back in. Use a torque wrench if you have one to ensure you don’t over tighten it. Check your manual for the recommended torque
  • Remove the oil cover and add 1.6 quarts of new oil.

Note: Check your level to make sure you don’t overfill the generator.

How do I reset my Onan generator

The process is similar to clearing codes on the generator. Hold down the power button for at least thirty seconds, restart the generator, and let in for fifteen minutes.

Onan generator won’t crank

The leading cause of this problem is a bad fuel pump. So first, check the fuel pump to see if it is damaged and repair or replace it as needed.

  • Disconnect the fuel hose going into the carburettor use the screwdriver to loosen the hose clamp
  • Point the hose into the bucket
  • Press the generator start or prime button press the left side of the start button
  • You should get a nice flow of fuel into the bucket if the fuel pump is working. If not, you’ll get a trickle or nothing
  • If no fuel comes out, order a new fuel pump since it’s likely deficient probably overheated. I had no fuel coming out when I ran this test on my generator
  • Then attach the fuel hose back on the carburettor

How to replace the fuel pump and the filter

Once you have determined that the pump is faulty beyond repair, the next step is to replace it.

Tools needed:

  1. T-30 TORX socket to remove the TORX screws
  2. Vice Grips to pinch the incoming fuel line from the gas tank
  3. A bucket or drip pan to place under the pinched fuel line in case it leaks
  4. 1/2-inch socket or wrench to remove the solenoid or grounding bolt

Follow these steps to replace the pump and filter;

  • Disconnect your RV from shore power
  • Disconnect the negative cable from your RV battery
  • Pinch the fuel line between the fuel tank and fuel filter attached to the fuel pump so that no fuel flows when you disconnect the hose
  • Place a drip pan below the left rear of the generator where the fuel pump is located to catch any fuel that runs out
  • Disconnect the fuel hose from both ends of the fuel pump and fuel filter. The drip pan should catch any gas that drips out
  • Remove everything blocking access to the fuel pump control board, solenoid, cables
  • Remove the bolts holding the fuel pump and remove the fuel pump and filter
  • Screw the new fuel filter into the new fuel pump and screw it in place
  • Attach the fuel lines to the new fuel pump/filter
  • Put all of the other stuff you removed back in reverse order
  • Remove the vice grips from the fuel line and check for leaks
  • Do a quick inspection to see if everything is put back together and connected
  • Reconnect power to your battery and shore power if necessary

Onan generator troubleshooting voltage regulator

Follow these steps to troubleshoot the voltage regulator;

  • Locate the voltage regulator inside the generator’s control box.
  • Test the voltage regulator’s pin 7 with a voltmeter.
  • The instrument should display 12 volts on pin 7.
  • Attach the voltmeter to the motor’s brushes.
  • The voltmeter should reflect 10 to 11 volts across the brushes.
  • The voltage regulator has failed if the voltmeter displays no voltage across the brushes.

Note: ensure the voltmeter’s leads are properly secured. Ensure the negative lead is connected to the ground when the positive lead is attached to pin 7. The displayed voltage value is incorrect if the negative information is not grounded.

Onan generator not charging the battery

Here are some of the most common reasons why your generator is not charging the batteries:

  • Corroded battery connections
  • The batteries are not holding charge
  • Damaged converters cooling fan
  • Faulty converter’s thermal sensor
  • Failure of a diode or other circuit board component
  • Corrosion on the circuit board itself
  • Faulty circuit breaker or fuse

Note; eliminated the root cause by inspecting all the parts mentioned above and replace or repair as needed.

Onan generator not getting fuel

Ensure that your generator has more than a 1/4 tank of fuel. If you have a 1/4 tank or less fuel, your generator will no longer be able to get gas from the gas tank. Then check the fuel filter to see if they are clogged and replace them. Then inspect the fuel line for any cracks and leaks and replace them as needed.

Onan generator not starting just clicking

The most common cause of this is a bad battery, but it can also be dirty/poor connections at the cables or not even having the batteries turned on if you have a master switch. A continuous rapid clicking while trying to start the generator signifies that there is not enough battery voltage getting to the starter solenoid.

That continuous rapid clicking is a sign that not enough voltage is getting to the starter solenoid. First, check your battery cables. Make sure the connections are clean and tight. Pay special attention to the ground cable that runs between the generator and the coach frame.

If the cables are good, you need to take the battery in and have it load tested. Do not rely on a voltmeter or battery charger to tell you if the battery is good or not. Remember, a bad battery can still read fully charged with 12V but not have enough capacity to do any work.

Onan generator troubleshooting no spark

If you are getting no spark at the spark plugs, remove the plug wires and check for continuity. No continuity means a faulty wire. Replace both of them. If there is no spark after the wire replacement, this indicates that the spark plug is defective and should be replaced.

Alternatively, the carburetor might be clogged due to stagnant, sticky fuel in the generator left for an extended period.  The denatured fuel can clog up the carburetor and prevent the engine from starting.

Note: Verify the condenser is not grounded. Remove the condenser and check for continuity. Place the voltmeter between the end of the wire and the mounting bracket of the condenser.

Onan generator won’t stay running

These are the leading causes of the problem;

  • Low air intake

As the oil in the generator gets warmer, it thins out just enough that it may fall below the proper level and shut down the generator. Check the oil level in your generator and refill if needed. You can also change the oil filter at this point.

  • Low fuel intake

Check the fuel line leading to your generator for any leaks. Then repair or replace it as needed.

  • Defective overload detector or Overspeed signal

Replace the spark plugs as they may be causing the generator to shut down.

Why is my Onan generator light blinking?

A blinking start light indicates a stored “trouble code”. Refer to your owner’s manual to retrieve the code. If you quickly press the start button 3 or 5 times and then blink the code.

Check this too: Murray M2500 Weed Eater How to & Troubleshooting Guide

Onan generator not priming

It is important to note that your generator will not make the expected fuel pump noise if it is already primed and has pressure. If the pump has pressure, it will remain quiet.

Follow these steps to see if the generator is priming;

  • Remove the fuel line from the carburettor, and place it into an empty container.
  • Then press and hold the prime switch. If fuel flows, it is priming.
  • Remove the supply line from the filter, and attach a length of fuel hose to the filter.
  • Place the end of the hose into a gas can.
  • Now press and hold the ‘STOP/PRIME’ button again, for about 10 seconds.
  • If you still do not get sufficient fuel flow, the pump is bad and needs to be replaced.

Note: The supply line is attached to the pump, underneath the set, in the front left corner. The fuel line connects to the fuel filter, which is screwed directly into the pump.

Oscar

In his spare time, Oscar loves tinkering with electronics. Solar panels, wiring, old TVs and sometimes DIY powerwalls. When he is not busy trying not to electrocute himself, you can find him in the garden tending to his vegetables and chickens.

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