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DTC B1021 Driver Deployment Loop Resistance High
The Air bag module monitors the circuit below for high resistance by perfoming a voltage drop on the circuit, if resistance higher than normal is found this will set the DTC.
Possible problems are a faulty air bag on the steering wheel, a faulty clock spring(module coil) or a problem with the wiring from the coil to the module.
I have found a lot of the time this code can come from the connector at the base of the column, look for a yellow 2 wire connector at the base of the steering column and then disconnect inspecting the terminals if no corrosion is found reconnect and clear DTC, By simply disconnecting and reconnecting the connector the code will usually go away.
If this does not work then there are special tools needed to diagnose the circuit, GM has a tool that is connected to the 2 wire connector that simulates the proper resistance in the circuit and then the reisitance is measured on the scan tool, thereby isolating the problem.