DTC U2004: Transmitted SPI Data Output Low: Description
WARNING: This page is about a different car, the 1998 Oldsmobile Cutlass and 1998 Chevrolet Malibu. However, it is still accessible from the selected car via links, so may be relevant.
DTC U2004 indicates that BFC has detected a short to ground or open on SPI data line from instrument cluster to BFC. DTC U2004 will set when Ignition 0 is active, and when first data byte transmitted to instrument cluster does not have feedback for 64 transmission cycles.
When DTC U2004 is set, THEFT SYSTEM, ABS, and SERVICE VEHICLE SOON indicators will illuminate, fuel and temperature gauges will read zero, and PRNDL indicator will be blank. DTC U2004 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.