Onan 5500 Code 27, help isolate?

[nemloc]

Hi folks,
I have a GD3270BH from 2019 with a factory installed Onan 5500 (QG 5500 LP, HGJAB series K).
I've not really used it beyond a test hour initially and running it for 15-20 mins regularly to keep it in working condition. I just went to start it as usual to make sure all is good and it starts but immediately shuts off. The service code is 27 which is a Voltage Sense code. I'm not seeing any issue anywhere else in the RV and things are working fine otherwise. I also get the same result whether or not I start it from the inside switch or the on-generator switch, whether the breakers on the generator are on or off, and whether the RV is plugged into shore power or not.

Based on the little info that I've found out there, it sounds like I probably have a short or broken wire that the generator is connected to but nothing is obvious. I removed the walls and tracked down the wire harnesses without obvious luck. ie: nothing looks melted or corroded or pest infested, etc.

Does anyone have any suggestions for:
a. procedure to troubleshoot? where should I be measuring?
b. a way to isolate the generator from the rv to see if there's an issue in the connectors or control boards vs in a wire bundle in the rv?
c. does a code 27 usually indicate something else?

Thanks for any help.

[howson]

nemloc -- welcome to the forum. Check out the letter to new members when you get a chance.

I don't want to misrepresent my expertise (which is next to nil) on generators. The information below is from my school documents (I attended RVSA) and my troubleshooting for "real" can be counted in hours on one day. With that said, the information below is from a Onan troubleshooting list I found from school. I hope it helps (and if someone else here has more practical experience then by all means follow their inputs!).

4. CHECK IF ENGINE KEEPS RUNNING The most common complaint is that the engine starts but will not keep running when the START switch is released. This happens because the control board will not allow the engine to continue running if the generator is not producing voltage or if the oil pressure signal is not present. See CONDITIONS REQUIRED TO KEEP RUNNING on the Troubleshooting Chart (I could not find this in the document/chart in the file!) for your model. If the engine will not keep running, do the following:
A1. Generator AC Output Check the generator AC output voltage as soon as the engine starts. Models showing “B1-B2 Volts” or “L1 AC Volts” under CONDITIONS REQUIRED TO KEEP RUNNING need this
AC voltage to keep running. Read between the points shown on the Troubleshooting Chart. If the AC voltage readings are good, proceed to “B” below.

A2. Field Flash If there is no AC, check for 10-12 VDC at the FIELD FLASH pin of the control boardduring cranking. If the field flash voltage is not present, the control board is defective. If the field flash
voltage is present, the wiring or regulator may be defective. To eliminate the wiring, check continuity between the FIELD FLASH pin of the control board and pin 7 of the regulator. If the continuity is good,
either the regulator or the field circuit (rotor and brushes) may be the problem.

A3 Field Circuit Check the field circuit by unplugging the regulator and measuring the resistance between pins 9 and 10 of the regulator’s mating plug. This reading should be 22 to 28 ohms. If this reading is too
high, check the brushes and/or clean the slip rings (use the Slick Stick, or a similar tool). If this reading is too low, there may be a short in the rotor. Also, check the resistance from pins 9 and 10 to ground. This
reading should be very high or infinity. If not, there is likely a ground in the rotor. If these reading are all good, the regulator is likely defective.

A4 External Excitation To confirm that the regulator is defective, turn off the generator’s AC circuit breaker(s), reconnect the regulator and apply 12 volts through a diode to pin 9 of the regulator plug (see
illustration) while attempting to start the engine. CAUTION: DO NOT attempt this without the diode. If you do, there will be fireworks! Remove the 12 volts within 1-2 seconds after the engine starts. If the
genset now continues to run and produces normal AC voltage, the generator is OK and the regulator is defective. If the genset does not continue to run but produces about 40% of normal AC voltage, again the
generator is OK and the regulator is defective. If no AC voltage is produced, the generator may have a problem that is beyond the scope of this guide. Re-check all wiring for security and signs of damage. It may
be necessary to take the unit to a qualified repair shop.

B. Check the oil pressure switch as soon as the engine starts. Models showing “LOP to GND” under CONDITIONS REQUIRED TO KEEP RUNNING need the oil pressure switch to be closed to ground when running. If the voltage on the LOL/LOP SW pin of the control does not go to near zero, the switch is not closing. These switches sometimes stick open if the generator has not been used or exercised often enough. Multiple start/stop cycles and/or tapping on the oil pressure switch will sometimes fix it. It may be necessary to temporarily jumper the switch to ground to keep the engine running. This can be done at the switch or at the OIL LOL/LOP SW pin on the control board. Models showing “LOP Open” under CONDITIONS REQUIRED TO KEEP RUNNING have electronic governors and require the low oil pressure switch to be closed at starting but open during running. When the switch opens, the governor module places a ground on the oil pressure input of the control board (P1-5). It is OK to temporarily ground P1-5 on this model to keep the engine running. NOTE: See chart for oil pressure and oil level switch locations.

C. If there is AC voltage present on B1-B2 or L1 AC, as applicable, and the correct oil pressure/level signal is present at the OIL LOL/LOP SW input of the control board, and the engine will not keep running, the control board is defective.

[nemloc]

Thanks for all that info, any chance to get the chart and diagram that it's referring to? otherwise it's kind of hard to figure out which part and which pins are being described.
Is this something that is usually under warranty? or only in the first year?

[howson]

Thanks for all that info, any chance to get the chart and diagram that it's referring to? otherwise it's kind of hard to figure out which part and which pins are being described.
Is this something that is usually under warranty? or only in the first year?

For some reason that chart is not in the document. The only applicable part is what I posted. Hoped it would help lead you to better, more complete info. Again, I'm no expert on the generator--was trying to help.

[JBill9694]

nemloc, did you get a CD with the owner's manual for the generator in your document package? The manual can also be downloaded as a searchable PDF. Section 11 is trouble shooting and there is a section on fault code 27.

[Guest]

Hi folks,
I have a GD3270BH from 2019 with a factory installed Onan 5500 (QG 5500 LP, HGJAB series K).
I've not really used it beyond a test hour initially and running it for 15-20 mins regularly to keep it in working condition. I just went to start it as usual to make sure all is good and it starts but immediately shuts off. The service code is 27 which is a Voltage Sense code. I'm not seeing any issue anywhere else in the RV and things are working fine otherwise. I also get the same result whether or not I start it from the inside switch or the on-generator switch, whether the breakers on the generator are on or off, and whether the RV is plugged into shore power or not.

Based on the little info that I've found out there, it sounds like I probably have a short or broken wire that the generator is connected to but nothing is obvious. I removed the walls and tracked down the wire harnesses without obvious luck. ie: nothing looks melted or corroded or pest infested, etc.

Does anyone have any suggestions for:
a. procedure to troubleshoot? where should I be measuring?
b. a way to isolate the generator from the rv to see if there's an issue in the connectors or control boards vs in a wire bundle in the rv?
c. does a code 27 usually indicate something else?

Thanks for any help.

Unless the issue is obvious, Its best to take the unit to a dealer who can make the repair and save you from a great deal of frustration IMHO. If you have some down time such as winter storage, this may be a good time to get the repair done. Then test it thoroughly under high load to ensure the repair was done correctly.

The electrical side can easily fall outside the norm for customer repairs.

Jim

[colan]

No generator expert, I’ve attached the service manual for the generator I think you have.