Compression Ignition Addict
Join Date: Dec 2007
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Here's what I have on a 1271;
P1271–1278-High To Low Side Open, Cylinders No.1–8
AB6 DIAGNOSTIC TROUBLE CODES (DTCs) P0262, P0265, P0268, P0271, P0274, P0277, P0280, P0283 and P1261-P1268: CHECK FOR SHORT TO B+ OR TO HIGH SIDE IN THE LOW SIDE CIRCUIT
* DTCs P1261-P1268 indicate that the low side circuit is shorted to B+ or the high side circuit between the IDM and the injector. The following table lists the circuits to inspect while performing these pinpoint tests, based o the DTC retrieved during the KOEO On-Demand or Injector Electrical Self Tests.
Cyl. DTC Low Side High Side
1 P1261-P0262 555 (T) 1087 (O)
2 P1262-P0265 556 (W) 878 (PK/Y)
3 P1263-P0268 557 (BR/Y) 1087 (O)
4 P1264-P0271 558 (BR/LB) 878 (PK/Y)
5 P1265-P0274 559 (T/BK) 1087 (O)
6 P1266-P0277 560 (LG/O) 878 (PK/Y)
7 P1267-P0280 561 (T/R) 1087 (O)
8 P1268-P0283 562 (LB) 878 (PK/Y)
* Key on/engine off.
* Disconnect IDM.
* Disconnect both connectors on the bank with the code.
* Measure resistance between the low side and battery positive post, then to high side at the injector valve cover connector. Refer to injector illustration at beginning of this pinpoint test for pin location.
Are both resistance readings less than 10,000 ohms?
GO to AB7 . REPAIR short in circuits between IDM and injector valve cover connector. RERUN Scan Tool Diagnostic Test.
AB7 CHECK FOR SHORT INTERNAL TO VALVE COVER
* Key off.
* Install Rotunda Glow Plug Injector Adapter 014-00935 or equivalent to valve cover gasket.
* Measure resistance between high side and low side circuits.
Is resistance less than 2.0 ohms on a cold engine?
GO to AB8 . Fault may be intermittent. GO to AB10 .
AB8 CHECK FOR SHORT UNDER VALVE COVER
* Key off.
* Remove valve cover.
* Disconnect injector connector.
* Measure resistance between Rotunda Glow Plug Injector Adapter 014-00935 or equivalent and injector connector on both high and low side circuits.
Is resistance greater than 10,000 ohms?
REPLACE injector. RERUN Scan Tool Diagnostic Test. GO to AB9 .
AB9 GASKET HARNESS OR UVC SHORT LOW SIDE TO HIGH SIDE
* Remove UVC harness.
* Measure resistance between gasket harness low side and high side circuitry.
Is resistance less than 5 ohms?
REPLACE gasket harness. RERUN Scan Tool Diagnostic Test. REPLACE UVC harness. RERUN Scan Tool Diagnostic Test.
AB10 CHECK FOR INTERMITTENT LOW SIDE SHORT TO B+ OR HIGH SIDE
* Key on/engine off.
* IDM disconnected.
* All four valve cover connectors disconnected.
* Using a digital multimeter and the flex tips supplied with the NGS Tester, measure resistance between the suspect injector low side circuit and battery positive post, then to high side circuit on the IDM connector. Refer to injector illustration at the beginning of this pinpoint test for pin location.
* Grasp the harness close to the suspect injector connector. Wiggle and shake harness while working toward the IDM.
Do either resistance readings ever drop below 10,000 ohms?
ISOLATE shorted circuit and REPAIR. CLEAR DTCs and RETEST. IDM internal failure. REPLACE IDM.