Engine fan wont turn off

[Chamberpains]

He originally stated that there is no check engine light and that the fan free spins at start up then locks up. Pending a problem with the A/C system, there aren't to many other ways this can happen without a CEL. The reason I asked about the EGR operation is because yes, tuners are notorious for suppressing codes and check engine lights. Some of these codes that are known to be suppressed can take time to come on. Yes, even 7.5 months. Then something happens that the ECM sees and it goes to let you know through the (CEL) check engine light. But low and behold the tuner turned off the ECM's ability to turn the CEL on and alert the operator. Some of the codes that deal with EGR and the turbo do infact kick the fan on. For all this guy knows, the ECM is logging the code and saying it sees a problem but simply can't turn the CEL on to tell him what it sees. This is 1 of the many reasons Insite is so vital to troubleshooting these engines.

JimT the OP has a CM870. They are EGR valve only. They do not have any other dpf, doc, scr after treatment devices.