Injector Driver Circuit Operation

1994 PCED OBDI-A

SECTION 18A: Diesel Diagnosis — 7.3L DI Engine

AB: Injector Driver Circuit Operation

AB1 CHECK FOR GROUND SHORT IN CIRCUIT BETWEEN IDM AND 42-WAY CONNECTOR

DTCs 921-928 indicate a low side ground short in the circuit between the IDM and the injector. The following table lists the circuit to inspect while performing these Pinpoint Tests, based on the DTC retrieved during the KOEO test.

DTC	Circuit	DTC	Circuit
921	555 (T)	925	559 (T/BK)
922	556 (W)	926	560 (LG/O)
923	557 (BR/Y)	927	561 (T/R)
924	558 (BR/LB)	928	562 (LB)

Key off.
Disconnect IDM harness connector.
Disconnect 42-way harness connector.
Measure resistance between circuit and chassis ground between IDM and 42-way connector. Refer to injector illustration before this test for pin location.

Is resistance less than 5 ohms?

Yes	No
REPAIR ground short in circuit between IDM and 42-way connector. RERUN Scan Tool Diagnostic Test.	GO to AB2.

AB2 CHECK FOR GROUND SHORT IN CIRCUIT BETWEEN 42-WAY CONNECTOR AND INJECTOR VALVE COVER CONNECTOR

Disconnect injector valve cover connector.
Measure resistance between circuit and ground between 42-way connector and valve cover connector.

Is resistance less than 5 ohms?

Yes	No
REPAIR ground short in circuit between 42-way connector and valve cover connector. RERUN Scan Tool Diagnostic Test.	GO to AB3.

AB3 IDM INTERNAL SHORT

Install Rotunda Glow Plug/Injector Adapter 014-00935.
Measure the injector resistance low side to the chassis ground.

Is the resistance less than 5 ohms?

Yes	No
GO to AB4.	IDM internal ground short. REPLACE IDM. RERUN Scan Tool Diagnostic Test.

AB4 INJECTOR INTERNAL GROUND SHORT

Remove valve cover.
Remove injector connector.
Measure the resistance of the injector low side to the chassis ground.

Is resistance less than 5 ohms?

Yes	No
Ground short in gasket harness. REPLACE gasket harness. RERUN Scan Tool Diagnostic Test.	Injector internal ground short, REPLACE damaged injector. RERUN Scan Tool Diagnostic Test.

AB5 CHECK FOR SHORT TO POWER (B+) IN CIRCUIT BETWEEN IDM AND 42-WAY CONNECTOR

DTCs 931-938 indicate a low side short to battery in the circuit between the IDM and the injector. The following table lists the circuit to inspect while performing these Pinpoint Tests, based on the DTC retrieved during the KOEO test.

DTC	Circuit	DTC	Circuit
931	555 (T)	935	559 (T/BK)
932	556 (W)	936	560 (LG/O)
933	557 (BR/Y)	937	561 (T/R)
934	558 (BR/LB)	938	562 (LB)

Key off.
Disconnect IDM harness connector.
Disconnect 42-way harness connector.
Measure voltage between circuit and chassis ground between IDM and 42-way connector. Refer to injector illustration for pin location before running this test.

Is B+ present?

Yes	No
REPAIR battery short in circuit between IDM and 42-way connector. RERUN Scan Tool Diagnostic Test.	GO to AB6.

AB6 CHECK FOR SHORT IN TO POWER (B+) CIRCUIT BETWEEN 42-WAY CONNECTOR AND INJECTOR VALVE COVER CONNECTOR

Disconnect injector valve cover connector.
Connect a valve cover harness jumper wire.
Measure voltage between circuit and ground between 42-way connector and valve cover connector.

Is B+ present?

Yes	No
REPAIR battery short in circuit between 42-way connector and valve cover connector. RERUN Scan Tool Diagnostic Test.	IDM internal battery short. REPLACE IDM. RERUN Scan Tool Diagnostic Test. If Codes 941-948 are present, GO to AB7.

AB7 CYLINDER NON-CONTRIBUTING — KOER TEST

DTCs 941-948 indicate a non-contributing cylinder has been detected during the KOER Cylinder Contribution Test (CCT).

Possible causes:

High or low side circuit damage.
Restricted or damaged fuel injector.
Base engine concern.

Perform KOEO injector buzz test.

Are any high side/low side DTCs present? (Refer to Diagnostic Trouble Code Description.)

Yes	No
SERVICE high side/low side concern. RERUN Scan Tool Diagnostic Test.	SERVICE base engine/injector concern as necessary. RERUN Scan Tool Diagnostic Test. GO to AB8.

AB8 CHECK FOR SHORT IN CIRCUITS BETWEEN IDM AND 42-WAY CONNECTOR

DTCs 961-968 indicate a high side to low side short in the circuit between the IDM and the injector. The following table lists the circuits to inspect while performing these Pinpoint Tests, based on the DTC retrieved during the KOEO test.

DTC	Low Side	High Side
961	555 (T)	1091 (O)
962	556 (W)	878 (PK/Y)
963	557 (BR/Y)	1091 (O)
964	558 (BR/LB)	878 (PK/Y)
965	559 (T/BK)	1091 (O)
966	560 (LG/O)	878 (PK/Y)
967	561 (T/R)	1091 (O)
968	562 (LB)	878 (PK/Y)

Key off.
Disconnect IDM harness connector.
Disconnect 42-way harness connector.
Measure resistance between the high side to low side between the IDM and 42-way harness connector. Refer to injector illustration for pin location.

Is the resistance less than 5 ohms?

Yes	No
REPAIR short in circuits between IDM and 42-way connector. RERUN Scan Tool Diagnostic Test.	GO to AB9.

AB9 CHECK FOR SHORT IN CIRCUITS BETWEEN INJECTOR VALVE CONNECTOR AND 42-WAY CONNECTOR

Key off.
Disconnect injector valve cover connector.
Measure resistance between injector cover connector and 42-way harness connector on high side and low side circuits.

Is resistance less than 3 ohms?

Yes	No
REPAIR short in circuits between 42-way connector and valve cover connector. RERUN Scan Tool Diagnostic Test.	GO to AB10.

AB10 CHECK FOR SHORT IN CIRCUITS BETWEEN INJECTOR CONNECTOR AND VALVE COVER CONNECTOR

Key off.
Remove valve cover.
Install Rotunda Glow Plug Adapter 014-00935.
Measure resistance between valve cover and injector on high and low side circuits.

Is resistance less than 5 ohms?

Yes	No
REPLACE gasket harness. RERUN Scan Tool Diagnostic Test.	GO to AB11.

AB11 CHECK INJECTOR FOR SHORT

Measure resistance between injector low side to high side.

Is resistance 1.5-4.5 ohms?

Yes	No
IDM internal short high side to low side. REPLACE IDM. RERUN Scan Tool Diagnostic Test.	REPLACE injector. RERUN Scan Tool Diagnostic Test. If Codes 971-978 are present, GO to AB12.

AB12 CHECK FOR OPEN BETWEEN INJECTOR HIGH SIDE TO LOW SIDE AT VALVE COVER CONNECTOR

DTCs 971-978 indicate a low side to high side open in the circuit between the IDM and the injector. The following table lists the circuits to inspect while performing these Pinpoint Tests, based on the DTC retrieved during the KOEO test.

Note: If all of the DTCs associated with an entire bank are retrieved, the high side circuit is most likely open.

DTC	Low Side	High Side	Bank
971	555 (T)	1091 (O)	Right
972	556 (W)	878 (PK/Y)	Left
973	557 (BR/Y)	1091 (O)	Right
974	558 (BR/LB)	878 (PK/Y)	Left
975	559 (T/BK)	1091 (O)	Right
976	560 (LG/O)	878 (PK/Y)	Left
977	561 (T/R)	1091 (O)	Right
978	562 (LB)	878 (PK/Y)	Left

Key off.
Disconnect injector valve cover connector.
Install Rotunda Glow Plug/Injector Adapter 014-00935.
Measure resistance between the high side to low side on the injector. Refer to injector illustration for proper pin location.

Is the resistance between 1.5-4.5 ohms?

Yes	No
GO to AB14.	GO to AB13.

AB13 CHECK FOR OPEN BETWEEN HIGH SIDE AND LOW SIDE AT INJECTOR CONNECTOR

Key off.
Remove valve cover.
Disconnect injector connector.
Measure resistance between injector cover connector and injector connector on high side and low side circuits.

Is resistance less than 5 ohms?

Yes	No
REPLACE injector or UVC harness. RERUN Scan Tool Diagnostic Test.	REPLACE gasket harness. RERUN Scan Tool Diagnostic Test.

AB14 CHECK FOR OPEN IN CIRCUITS BETWEEN INJECTOR VALVE CONNECTOR AND 42-WAY CONNECTOR

Key off.
Disconnect 42-way harness connector.
Measure resistance between injector cover connector and 42-way harness connector on high side and low side circuits.

Is resistance less than 5 ohms?

Yes	No
GO to AB15.	REPAIR open in high side or low side circuits as required. RERUN Scan Tool Diagnostic Test.

AB15 CHECK FOR OPEN IN CIRCUITS BETWEEN 42-WAY CONNECTOR AND IDM CONNECTOR

Key off.
Disconnect IDM harness connector.
Measure resistance between IDM harness connector and 42-way harness connector on high side and low side circuits.

Is resistance less than 5 ohms?

Yes	No
IDM internal open circuit high to low side. REPLACE IDM. RERUN Scan Tool Diagnostic Test. If Codes 911 and 922 are present, GO to AB16.	REPAIR open in high side or low side circuits as required. RERUN Scan Tool Diagnostic Test.

AB16 CHECK FOR SHORT IN HIGH SIDE CIRCUIT BETWEEN IDM AND 42-WAY CONNECTOR

DTCs 991 and 992 indicate a ground short or short to battery exists on the high side circuit between the IDM and the injectors. The following table list the circuits to inspect while performing these pinpoint tests, based on the DTC retrieved during the KOEO test.

DTC	High Side	Bank
991	1091 (O)	Right
992	878 (PK/Y)	Left

Key off.
Disconnect IDM harness connector.
Disconnect 42-way harness connector.
Measure resistance between high side circuit and chassis ground between the IDM harness connector and the 42-way harness connector. Refer to injector illustration for proper pin location.

Is resistance less than 5 ohms?

Yes	No
REPAIR ground short in high side circuit between the IDM harness connector and the 42-way harness connector. RERUN Scan Tool Diagnostic Test.	GO to AB17.

AB17 CHECK FOR BATTERY SHORT ON HIGH SIDE CIRCUIT BETWEEN IDM AND 42-WAY CONNECTOR

Key off.
IDM harness connector disconnected.
42-way harness connector disconnected.
Measure resistance between high side circuit and B+ terminal between the IDM harness connector and the 42-way harness connector.

Is resistance less than 5 ohms?

Yes	No
REPAIR battery short in high side circuit between the IDM harness connector and the 42-way harness connector. RERUN Scan Tool Diagnostic Test.	GO to AB18.

AB18 CHECK FOR GROUND SHORT IN HIGH SIDE CIRCUIT BETWEEN 42-WAY CONNECTOR AND INJECTOR VALVE COVER HARNESS

Key off.
42-way harness connector disconnected.
Disconnect injector valve cover connector.
Measure resistance between high side circuit and chassis ground between the 42-way harness connector and the injector valve cover connector.

Is resistance less than 5 ohms?

Yes	No
REPAIR ground short in high side circuit between the injector harness connector and the 42-way harness connector. RERUN Scan Tool Diagnostic Test.	GO to AB19.

AB19 CHECK FOR BATTERY SHORT ON HIGH SIDE CIRCUIT BETWEEN 42-WAY CONNECTOR AND INJECTOR VALVE COVER HARNESS

Key off.
42-way harness connector disconnect.
Disconnect injector valve cover connector.
Measure resistance between high side circuit and B+ terminal between the injector valve cover connector and the 42-way harness connector.

Is resistance less than 5 ohms?

Yes	No
REPAIR battery short in high side circuit between the injector valve cover connector and the 42-way harness connector. RERUN Scan Tool Diagnostic Test. If Codes 993 and 994 are present, GO to AB20.	INTERNAL ground or battery short in IDM. REPLACE IDM. RERUN Scan Tool Diagnostic Test.

AB20 CHECK FOR OPEN IN HIGH SIDE CIRCUIT BETWEEN IDM AND 42-WAY CONNECTOR

DTCs 993 and 994 indicate an open circuit exists on the high side circuit between the IDM and the injectors. The following table lists the circuits to inspect while performing these Pinpoint Tests, based on the DTC retrieved during the KOEO test.

DTC	High Side	Injector Bank
993	1091 (O)	Right
994	878 (PK/Y)	Left

Key off.
Disconnect IDM harness connector.
Disconnect 42-way harness connector.
Measure resistance on the high side circuit between the IDM harness connector and the 42-way harness connector.

Is resistance less than 5 ohms?

Yes	No
GO to AB21.	REPAIR open in high side circuit between the IDM harness and the 42-way harness connector. RERUN Scan Tool Diagnostic Test.

AB21 CHECK FOR OPEN IN HIGH SIDE CIRCUIT BETWEEN 42-WAY CONNECTOR AND INJECTOR VALVE COVER HARNESS

Key off.
42-way harness connector disconnected.
Disconnect injector valve cover connector.
Measure resistance in high side circuit between the 42-way harness connector and the injector valve cover connector. Refer to injector illustration for pin location.

Is resistance less than 5 ohms?

Yes	No
GO to AB22.	REPAIR open in high side circuit between the injector harness connector and the 42-way harness connector. RERUN Scan Tool Diagnostic Test.

AB22 CHECK INJECTOR RESISTANCE

Key off.
Injector valve cover connector disconnected.
Install Rotunda Glow Plug/Injector Adapter 014-00935.
Measure resistance between high side and low side injector terminals.

Is resistance 1.5-4.5 ohms?

Yes	No
INTERNAL open in IDM. REPLACE IDM. RERUN Scan Tool Diagnostic Test.	GO to AB23.

AB23 CHECK GASKET HARNESS FOR OPEN

Remove valve cover.
Disconnect injector harness connector.
Measure resistance between injector connector and chassis ground.

Is resistance less than 5 ohms?

Yes	No
OPEN injector. REPLACE injector. RERUN Scan Tool Diagnostic Test.	OPEN gasket or UVC harness. REPLACE gasket or harness. RERUN Scan Tool Diagnostic Test. If DTC Codes 995-996 are present, GO to AB24.

AB24 MULTIPLE CONCERNS — RIGHT OR LEFT BANK

DTCs 995 and 996 indicate multiple concerns exist on the right or left injector bank along with a low side concern. DTCs 921-928 and 931-938 and one or more high side codes will be stored with DTCs 995 and 996.

Repair low side concern. For DTCs 921-928 go to AC1. For DTCs 931-938 go to AC4.
Rerun KOEO test.

Are low side DTCs cleared?

Yes	No
SERVICE high side DTCs. REFER to appropriate test step in this pinpoint test.	REPEAT this step until all low side DTCs are cleared. SERVICE high side DTCs. REFER to appropriate test step in this pinpoint test.

AB25 CHECK FOR SHORT IN CIRCUITS BETWEEN IDM HARNESS CONNECTOR AND 42-WAY CONNECTOR

DTC 997 indicates the high side circuits 1091 (O) and 878 (PK/Y) are shorted together.

Key off.
Disconnect IDM harness connector.
Disconnect 42-way harness connector.
Measure resistance between the high side to low side between the IDM and 42-way harness connector.

Is the resistance less than 5 ohms?

Yes	No
REPAIR short in circuits between IDM and 42-way connector. RERUN Scan Tool Diagnostic Test.	GO to AB26.

AB26 CHECK FOR SHORT IN CIRCUITS BETWEEN INJECTOR VALVE CONNECTOR AND 42-WAY CONNECTOR.

Key off.
Disconnect injector valve cover connector.
Measure resistance between injector cover connector and 42-way harness connector on high side and low side circuits.

Is resistance less than 5 ohms?

Yes	No
REPAIR short in circuits between 42-way connector and valve cover connector. RERUN Scan Tool Diagnostic Test.	IDM high sides shorted internally. REPLACE IDM. RERUN Scan Tool Diagnostic Test.