Engine systems sold in the U.S. must be certified to comply with the EPA and CARB emission standards. EPA and CARB regulations require that in-use testing be performed on vehicles by the emission certificate holder and reported to the EPA and CARB in order to ensure ongoing compliance with these emission standards. We are the holder of this emission certificate for our engines, including engines installed in certain vehicles with one customer for which we did not also manufacture or sell the emission aftertreatment system. During 2015, a quality issue in certain of these third party aftertreatment systems caused some of our inter-related engines to fail in-use emission testing. In the fourth quarter of 2015, the vehicle manufacturer made a request that we assist in the design and bear the financial cost of a field campaign to address the technical issue purportedly causing some vehicles to fail the in-use testing.
As the certificate holder, we recorded a charge of $60 million in 2015 for the expected cost of the proposed voluntary campaign. The campaign design was finalized with our original equipment manufacturer (OEM) customer, reviewed with the EPA and submitted for final approval in 2016. We concluded based upon additional in-use emission testing performed in 2016 that the campaign should be expanded to include a larger population of vehicles manufactured by this one OEM. We recorded additional charges of $138 million in 2016 to reflect the estimated cost of our overall participation in the campaign.
In late 2016, litigation arose with our OEM customer regarding cost allocation for this campaign. In January 2018, a settlement was reached with our customer to fully resolve this matter, which resulted in an incremental charge of $5 million recorded in the fourth quarter of 2017.
Loans Payable and Commercial Paper
Loans payable at December 31, 2018 and 2017 were $54 million and $57 million, respectively, and consisted primarily of notes payable to financial institutions. The weighted-average interest rate for notes payable, bank overdrafts and current maturities of long-term debt at December 31 was as follows:
Weighted-average interest rate
We can issue up to $3.5 billion of unsecured, short-term promissory notes ("commercial paper") pursuant to our board authorized commercial paper programs. The programs facilitate the private placement of unsecured short-term debt through third party brokers. We intend to use the net proceeds from the commercial paper borrowings for general corporate purposes. We had $780 million and $298 million in outstanding borrowings under our commercial paper programs at December 31, 2018 and 2017, respectively. The weighted-average interest rate for commercial paper at December 31 was as follows:
Weighted-average interest rate
Revolving Credit Facilities
On August 22, 2018, we entered into a new five-year revolving credit agreement with a syndicate of lenders. The new credit agreement provides us with a $2 billion senior unsecured revolving credit facility until August 22, 2023. This credit agreement replaces the prior $1.75 billion five-year credit agreement that would have matured on November 13, 2020. Amounts payable under our revolving credit facility will rank pro rata with all of our unsecured, unsubordinated indebtedness. Up to $300 million under this credit facility is available for swingline loans. Advances under the facility bear interest at (i) a base rate or (ii) a rate equal to the LIBOR rate plus an applicable margin based on the credit ratings of our outstanding senior unsecured long-term debt. Based on our current long-term debt ratings, the applicable margin on LIBOR rate loans was 0.75 percent per annum as of December 31, 2018. Advances under the facility may be prepaid without premium or penalty, subject to customary breakage costs.
On August 22, 2018, we entered into a new 364-day credit agreement that allows us to borrow up to $1.5 billion of additional unsecured funds at any time through August 21, 2019. This credit agreement replaces the prior $1.0 billion 364-day credit