I paid off the auto loan years ago (2013). I have just noticed that my auto loan shows up on my TransUnion & Experian reports, but not my Equifax reports. I think it might be hurting my score because my Equifax report/score is reporting I have a lack of any new "non-mortgage installment loans". I was wondering if this is disputable/fixable?
Reporting to a specific CRA is totally optional, and is not disputable.
Many creditors do not even have a reporting agreement with all CRAs.
In order to report to a CRA, a party must establish a credit reporting agreement.
It costs them $ and also requires that they demonstrate ability to report using the automated system, including use of the electronic Metro 2 format and the use of the electronic e-Oscar system, which are required by the big-3 CRAs.
I was wondering if this is disputable/fixable?
You can't disput something if it isn't on a report. There's nothing to fix. Not all creditors report to all 3 of the major CRA's nor are they required to do so. You can't force them to report to a CRA that they do not normally report to. If, on the other hand, the creditor normally reports to EQ then contact the creditor about it.
If it was your only installment then it won't help Credit Mix anyway as it was paid off. Impact to other factors would depend on the specifics.