Test Procedure

WARNING: This page is about a different car, the 1989 Cadillac Allante. However, it is still accessible from the selected car via links, so may be relevant.

First check that the code is not intermittent.
This step determines if the fault is due to the power or ground circuits or the data line.
This step determines if the data line fault is in circuit 800E.
This step checks for ignition-3 to the programmer.
This step determines if the loss of ground is due to the programmer, wiring or the CPS.
This step checks if the data line fault is in circuit 800A or at the programmer.

Fig 1: DTC B337: Loss Of HVAC Programmer Data Flow Chart

Courtesy of GENERAL MOTORS CORP.