Chart G DERM Cannot Communicate Through the Serial Data Circuit

CIRCUIT DESCRIPTION
When the ignition switch is first turned to "ON," system voltage is applied from Fuse C-22 to the DERM at the "SIR Indicator High" input, terminal "B9," and to the "INFL REST" indicator (located in the instrument cluster) which is connected to the "SIR Indicator Low," terminal "A1." Fuse C-23 applies system voltage to the "Ignition 1" input, terminals "A3" and "B 3." The DERM responds by flashing the "INFL REST" indicator 7 to 9 times.

When the engine is being cranked, system voltage is applied from Fuse C-21 to the DERM and the "Crank" input, terminal "B10." The DERM responds by grounding the "SIR Indicator Low" output until system voltage is removed from the "Crank" input. This results in the "INFL REST" indicator being illuminated steady during cranking.

After cranking, the DERM will again flash the "INFL REST" indicator 7 to 9 times.

TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. An improper connection to the DERM-DLC will prevent communication from being established.
2. The correct "Body Systems" cartridge must be used.
3. This test checks for a short to ground in the "Serial Data" CKT 800.
4. This test checks for an open in the "Serial Data" CKT 800.
5. This test determines whether the fault is due to a short to B+ in the "Serial Data" CKT 800 or a faulty DERM.