The 1.5 dCi is extremely sensitive to voltage drops. A weak battery (below 11.5V during crank) or a loose alternator ground strap causes the ECUs to "brown out." When voltage dips, the digital signal becomes corrupted, triggering DF137.
That was fourteen months ago.
In return, the Clio had carried her through three divorces, one revolution (hers, failed), and the death of her daughter.