After replacing the wiring harness on the Diesel Exhaust Fluid (DEF) tank on some 2020-2022 Silverado 2500HD/3500HD and Sierra 2500HD/3500HD trucks equipped with the 6.6L Duramax diesel engine (RPO L5P), several DTCs may set. DTCs P20B9 (Reductant Heater 1 Control Circuit) and P20C1 (Reductant Heater 3 Control Circuit) may be caused by a wiring change to the service DEF tanks. (Fig. 5)
Fig. 5
If these conditions are found, examine the 16-pin wiring harness connector to verify which wiring harness is installed on the vehicle prior to ordering any parts. On the first-design DEF tank harness, pin location 12 will be empty. The second-design DEF tank harness, pin location 12 has a wire in the connector. (Fig. 6)
Fig. 6
For complete wiring pinout charts for the first-design harness and second-design harness, refer to #PIP5838.
– Thanks to John Stempnik