Check Engine Light

[tranquility]

After camp hosting at Seeley Lake Mt. for 5 months we drove about 1 1/2 hrs. to Bretz RV in Missoula Mt for lube, fuel filters, Lippert step recall and installation of Zamp Solar 340 watt kit and some roof repairs. No problems with anything.

Upon leaving Bretz on I-90 E the check engine light came on then off and on until I could reach an exit to pull off. About 10 miles. I checked every gauge possible, no indication of a problem. The engine temp went back and forth from 177 to 185. When checking the coolant reservoir I could see a small amount of coolant around the bottom of the cap. (16 psi.) and small air bubbles around the neck of the reservoir. I recall the tech. telling me how difficult it was to remove and to put the cap back on. I also have to stand on a step and push down hard to put the cap back on.

I had no problem returning to Bretz RV although the check engine light still went off and on. It was Sat. AM so I must wait to Monday to address the problem.

This reservoir is the thick polyurethane (I think) so may be welded? If so should I go to the 7 psi that some have done on this forum?

Should I drain and flush system? 37K miles, never a problem. If I need a new reservoir, where do I go? I always carry the Fleetguard ES complete and would use that for refill.

Please explain what triggered Engine Check light when all gauges (temp.) showed no issue.

[Mike and Cha]

I would doubt the check engine light is due to your coolant reservoir, or anything to do with the cooling system. Normally it comes on due to an electrical issue, or issues related to the pollution/emission control components of your engine. It could be something as simple as your gas cap not being on correctly. I was having chassis battery issues, and it eventually made the check engine light come on. I was sure I had a bigger problem. I called my mechanic and he suggested I just replace the battery, as constant low voltage from a bad battery could trigger the check engine light to come on. I changed the battery and everything went back to normal, and the check engine light has not come on again.

[William Willard]

Check the 12v connector on your fuel filter -- Maybe not on tight enough -- Bill Willard

[RileyCaton]

I would have a diesel tech read the ECM notes/error logs to see what was causing the problem.

I've installed Silverleaf in our 2006 Diplomat and can pull up an engine error window that provides a plain text message as it's happening. This was very handy when the engine went into de-rate in the middle of nowhere Nevada. I was able to assess what was going on and fortunately, an engine restart was all that was required.

[Mike Canter]

CELs are designed to mainly tell you that a sensor is detecting bad info or the sensor has failed. Seriously doubt that it is the coolant unless the level has dropped below a sensor. As far as the coolant temp fluctuation that is normal thermostat operation.

[tranquility]

First, Thank you for the suggestions. Upon returning to Bretz I checked the coolant reservoir and found the level to be near the max level but saw a few small air bubbles at the bottom of the cap neck. Tech had to push down hard to but the cap back on. New reservoir available at Monaco for $330.00. YIKES!! Next I checked the 12 v connection to the water in fuel filter, ok. Next checked the Primary fuel filter and found enough fuel dripping to wet my hand. On Monday AM tech came over and tightened the filter about 3/4 turn. He said that filter was on very tight when he took it off and put the new filter on hand tight. I then left for the Cummins shop for a computer diagnoses. No check engine light the 5 miles to Cummins. Computer showed the check engine light caused by fuel issue, most likely air in system. No problem after tightening filter. Computer did indicate an inactive fault with the crankcase pressure. Replaced the CCK breather filter. Now all good except replacing coolant reservoir.