Not assigned in the generic OBD-II standard - if your scan tool shows this code, it is manufacturer-specific; verify the meaning in your make's service information

C0020 (ABS pump motor circuit) on GM trucks is usually a failed pump motor inside the ABS hydraulic unit. The motor brushes wear out at 150K+ miles. Some shops rebuild these modules for ~$200, or buy a remanufactured unit. A failing pump motor often makes a loud buzzing from the hydraulic unit at key-on. Replacing the whole EBCM unit requires bleeding the ABS with a Tech 2 or equivalent. Note: this module has to be coded to the vehicle with a factory-level scan tool after installation. Budget for that step, or have a shop supply and code the part.

Trailblazer/Envoy C0020 is a well-known issue. The ABS pump motor connector on the EBCM develops solder joint failures from vibration and heat. A popular DIY fix is the "ABS EBCM solder repair" -- remove the module, open it, reflow the pump motor solder joints. Many owners have extended ABS life by 5+ years with this repair. If you are not comfortable soldering, buy a remanufactured module. Note: this module has to be coded to the vehicle with a factory-level scan tool after installation. Budget for that step, or have a shop supply and code the part.

Escalade/Yukon C0020 often throws alongside traction control and StabiliTrak lights. The root cause is usually the EBCM's pump motor driver circuit. A remanufactured EBCM is the most reliable fix. After swap, you must program the unit to the VIN and re-learn the steering angle sensor with a scan tool that supports GM ABS programming. Note: this module has to be coded to the vehicle with a factory-level scan tool after installation. Budget for that step, or have a shop supply and code the part.