Cummins ISB 5.9 Check Engine Light With No Stored Codes

[VolDawg]

Recently my check engine light illuminated. I have a 2000 Fleetwood Discovery with a Cummins ISB 5.9.

I took it to my local independent diesel repair shop. They scanned for codes and did not find any. They took the rig for several test drives and ran a diagnostic scan while driving. Still no stored codes. I had the shop install new fuel filters as the RV needed them and to ensure that was not causing any codes.

They suggested I may have electrical gremlins due to the age of the RV but insist the engine drives as it should with no codes. Coincidently, I had just performed my first DIY oil change.

I'm not sure where to go from here to figure out what is causing the check engine light. Any suggestions?

[Jon_C]

My rig has same motor but couple years older. On mine at least I found 2 switches under the dash near the column. One is a diagnostic switch the other an idle up /down switch just hanging there.

You can check for codes with these if you have them. Im betting if the light is lit it will flash the code.

Press diag switch and check engine light will flash the first code then press idle up for next code.

I can also read codes on mine with scangauge d but they can be cryptic.

I had a 6 month long battle where my scangage showed cryptic hexadecimal code that kept reoccurring but no check light and nothing with the switches.

Turned out my vp44 was going out, it can do strange things and throw strange code’s but still work. It finally started giving me a dead accelerator pedal periodically which is a sure sign of it going bad. Replaced and been fine since.

[VolDawg]

Originally Posted by Jon_C

My rig has same motor but couple years older. On mine at least I found 2 switches under the dash near the column. One is a diagnostic switch the other an idle up /down switch just hanging there.

You can check for codes with these if you have them. Im betting if the light is lit it will flash the code.

Press diag switch and check engine light will flash the first code then press idle up for next code.

I can also read codes on mine with scangauge d but they can be cryptic.

I had a 6 month long battle where my scangage showed cryptic hexadecimal code that kept reoccurring but no check light and nothing with the switches.

Turned out my vp44 was going out, it can do strange things and throw strange code’s but still work. It finally started giving me a dead accelerator pedal periodically which is a sure sign of it going bad. Replaced and been fine since.

Thank you for this tip. I have these switches under my dash but did not know I can use them to detect a code. As I shared in my post, my shop scanned and could not find codes. Maybe this solution will reveal something.

[Jon_C]

Your welcome! Let us know what you find.

[Hotwrench451]

Your engine may be too old for this, but its possible the maintenance feature is turned on in the features and parameters of the Engine control module software. The check engine light will illuminate after so many miles to remind you to change your oil. Any Cummins dealer can plug into your ECM to check and confirm this, or even turn off the feature if you wish.

[VolDawg]

Originally Posted by Hotwrench451

Your engine may be too old for this, but its possible the maintenance feature is turned on in the features and parameters of the Engine control module software. The check engine light will illuminate after so many miles to remind you to change your oil. Any Cummins dealer can plug into your ECM to check and confirm this, or even turn off the feature if you wish.

To be honest, I don't know if I have this feature, but I had just changed my engine oil before the CEL illuminated.

[Toribk]

Two things I would check if applicable to your 2000 Discovery.

Check the sensor at your Fuel/water separator along with the coolant level sensor on the reservoir.

On the 2012, both will trigger an amber Check Engine Light icon.

[VolDawg]

Originally Posted by Toribk

Two things I would check if applicable to your 2000 Discovery.

Check the sensor at your Fuel/water separator along with the coolant level sensor on the reservoir.

On the 2012, both will trigger an amber Check Engine Light icon.

I'll check the sensors. If it were the sensor, would it throw a code?

[Skip426]

Originally Posted by VolDawg

I'll check the sensors. If it were the sensor, would it throw a code?

The low coolant code ( if generated on a long climb , where coolant sloshes away from the sensor) may erase on level ground , when the sensor is again covered.
Even a quart low in the reservoir can cause this.

Was the light on when you got to the shop ?

[Jon_C]

Originally Posted by VolDawg

I'll check the sensors. If it were the sensor, would it throw a code?

My rig has a water in fuel light if the water level in filter gets too high. If I unplug it the light goes out. Bad design by the engineers using wrong type of circuit.

[VolDawg]

Originally Posted by Skip426

The low coolant code ( if generated on a long climb , where coolant sloshes away from the sensor) may erase on level ground , when the sensor is again covered.
Even a quart low in the reservoir can cause this.

Was the light on when you got to the shop ?

The light began to illuminate shortly after I changed the oil. I took it to the shop because of the CEL illumination. The shop could not find any visual issues nor were they able to find any stored codes.

[Toribk]

Just thought of something else since you mentioned it illuminated after you changed the oil.....did you pre-fill your oil filter before screwing it back on?

[Hotwrench451]

if the light came on after the oil change, definitely would take a hard look at the connector and wiring for the water in fuel sensor, they are very sensitive to any kind of moisture, and they arent very expensive either to change the sensor and pigtail. aside from that, get the codes pulled from either a local shop of you can purchase an inexpensive code reader like scan gauge.

[VolDawg]

Originally Posted by Toribk

Just thought of something else since you mentioned it illuminated after you changed the oil.....did you pre-fill your oil filter before screwing it back on?

Yes, I prefilled the oil filter.