The Auto Stop/Start function (RPO KL9) may be inoperative on some 2019-2021 Silverado 1500 and Sierra 1500 models. In addition, the Check Engine MIL may be illuminated and DTCs P3055 (DC/DC Converter Output Voltage 1 Performance) and P3056 (DC/DC Converter Output Voltage 2 Performance) may be set in the Engine Control Module.
If these conditions are found, check for the presence of fuses F51DR and/or F52DR in the X51R instrument panel fuse block, located behind the side trim panel on the right side of the instrument panel. (Fig. 19) These fuses should not be installed on vehicles equipped with Auto Stop/Start. These fuses will create an additional load for the T19 Power Supply Transformer, which will pull down the outlet voltage, causing the Auto Stop/Start system to not function.
Fig. 19
Verify that the correct fuses are installed in the F51DR, F52DR, F56DR and the F57DR locations of the X51R instrument panel fuse block.
- If the vehicle is equipped with Auto Stop/Start, there should not be any fuses in the F51DR and F52DR locations on the front of the fuse block. (Fig 20)
Fig. 20
- If the vehicle is equipped with Auto Stop/Start, verify fuses are present in the F56DR and F57DR locations on the back of the fuse block. (Fig. 21)
Fig. 21
- If all four fuse locations are correct, but the concern is still present, follow the diagnostic procedures in the appropriate Service Information.
There are two part numbers for the right instrument panel fuse block on light-duty pickups – one without the Auto Stop/Start feature (84582038) and one with the Auto Stop/Start feature (84582037). Vehicles with Auto Stop/Start but with the incorrect fuse block will have DTCs set for the DC/DC converter.
If the condition persists after confirming the fuse block is correct and, if necessary, removing or adding fuses as appropriate, begin diagnosis of the DC/DC converter as outlined in Service Information.
For additional information, refer to Bulletin #21-NA-121.
– Thanks to David MacGillis
