Fuel Delivery Command Signal

1994 PCED OBDI-A

SECTION 18A: Diesel Diagnosis — 7.3L DI Engine

T: Fuel Delivery Command Signal

DTC 956 indicates that the PCM has detected a concern on the FDCS line.

Possible causes:

Is voltage of 0.6 ± 0.1 volt present?

Yes	No, voltage of less than 0.5 volt present	No, battery voltage present
GO to T2.	GO to T3.	GO to T4.

With Super Star II tester connected follow on output state check procedure in Scan Tool Diagnostic Procedures Test Step 3.1.

Does output toggle between 0.6 ± 0.1 volt and battery voltage on Pin 95 and ground?

Yes	No
System OK.	CHECK for intermittent on Circuit 821 (BR/O).

Is resistance less than 5 ohms?

Yes	No
GO to T6.	REPAIR open in Circuit 821 (BR/O). RERUN KOEO test.

Is battery voltage present?

Yes	No
REPAIR short to battery voltage. RERUN test.	GO to T5.

Is there damage or corrosion on harness?

Yes	No
REPAIR damage to the connector. RERUN test.	REPLACE PCM. GO to T9.

Is the resistance less than 5 ohms?

Yes	No
REPAIR ground short in Circuit 821 (BR/O). RERUN test.	GO to T7.

Does system pass?

Yes	No
GO to T8.	REPLACE PCM. GO to T9.

Does system pass?

Yes	No
Carefully RECHECK IDM pins and harness connector for corrosion or damage. REPAIR as necessary. RETEST system.	Original IDM damaged. REPLACE with known good IDM.

Does system pass?

Yes	No
Original PCM damaged. REPLACE with known good PCM.	Carefully RECHECK PCM harness connector pins for open or short. REPAIR as necessary. GO to T10.

Does system pass?

Yes	No
Carefully CHECK PCM pins and connector for corrosion or damage.	PCM damaged. REPLACE with known good PCM.