DTC 21: Ignition Signal

When either cylinders No. 1, 3, 5 and 7 or cylinders No. 2, 4, 6 and 8 are all not operating, go to next step. If there is a different malfunction, go to step 3) or to step 4).
Check Ground Circuit - Turn ignition off. Disconnect Power Transistor Unit (PTU) harness connectors. Verify harness continuity between PTU harness connector terminals "f" and "l" (Black wire) and engine ground. See Fig 1 -Fig 8 . If continuity is present, go to step 4). If continuity is not present, repair harness or connectors as necessary and perform FINAL CHECK .

Fig 1: Locating Ignition Coil Relay
Courtesy of NISSAN MOTOR CO., U.S.A.

Fig 2: Locating EFI Sub-Harness Connector No. 4
Courtesy of NISSAN MOTOR CO., U.S.A.

Fig 3: Locating EFI Sub-Harness Connector No. 5
Courtesy of NISSAN MOTOR CO., U.S.A.

Fig 4: Locating PTU Harness Connector (Left Side)
Courtesy of NISSAN MOTOR CO., U.S.A.

Fig 5: Locating PTU Harness Connector (Right Side)
Courtesy of NISSAN MOTOR CO., U.S.A.

Fig 6: DTC 21, Checking Ground Circuit
Courtesy of NISSAN MOTOR CO., U.S.A.

Fig 7: Locating Ignition Coils (Right Side)
Courtesy of NISSAN MOTOR CO., U.S.A.

Fig 8: Locating Ignition Coils (Left Side)
Courtesy of NISSAN MOTOR CO., U.S.A.
Search For Malfunctioning Circuit Using CONSULT - Turn ignition off and connect CONSULT. Perform POWER BALANCE in ACTIVE TEST mode with CONSULT. Search for circuit which does not produce a momentary engine speed drop.
Check Output Signal Circuit - Turn ignition off. Disconnect ECM harness connector and PTU harness connector. Verify harness continuity between ECM harness connector terminals and PTU harness connector terminals as follows:
- ECM terminal No. 1 and PTU terminal "b" (Green wire).
- ECM terminal No. 2 and PTU terminal "j" (Yellow wire).
- ECM terminal No. 3 and PTU terminal "d" (Green/White wire).
- ECM terminal No. 11 and PTU terminal "a" (Yellow/White wire).
- ECM terminal No. 12 and PTU terminal "k" (Green/Black wire).
- ECM terminal No. 13 and PTU terminal "e" (Yellow/Black wire).
- ECM terminal No. 14 and PTU terminal "g" (Green/Red wire).
- ECM terminal No. 15 and PTU terminal "h" (Yellow/Red wire).
See Fig 9 . If continuity is present, go to next step. If continuity is not present, verify harness continuity between ECM connector and PTU connector. Repair harness or connectors as necessary.
Check Component - Inspect power transistor unit. See I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. Replace power transistor unit if necessary and perform FINAL CHECK .

Fig 9: DTC 21, Checking Output Signal Circuit

Courtesy of NISSAN MOTOR CO., U.S.A.