DTC 21: Ignition Signal

Check Power Supply - Turn ignition off. Disconnect ignition coil harness connector. See Fig 1 . Turn ignition on. Measure voltage between ignition coil harness connector terminal "a" and ground. See Fig 4 . If battery voltage is not present, check wire between ignition coil and ignition switch for open or short circuit. If battery voltage is present, go to next step.
Check Ground Circuit - Turn ignition off. Disconnect power transistor and resistor/condenser wiring harness connector. See Fig 2 and Fig 3 . Check continuity between ignition coil connector terminal "b" and following: power transistor connector terminal "i" and resistor/condenser connector terminal "d". See Fig 5 . Check continuity between power transistor connector terminal "h" and engine ground. If continuity is present, go to next step. If continuity is not present, repair harness or connectors as necessary.
Check Input Signal Circuit - Turn engine off. Leave power transistor and resistor/condenser wiring harness disconnected. Disconnect ECM harness connector. Check continuity between resistor/condenser connector terminal "c" and ECM terminal No. 3. See Fig 6 . If continuity is present, go to next step. If continuity is not present, repair harness or connectors as necessary.
Check Output Signal Circuit - Ensure ignition is off. Check for continuity between ECM terminal No. 1 and power transistor connector terminal "g". See Fig 7 . If continuity is present, inspect ignition coil and power transistor. See SYSTEM/COMPONENT TESTS article in the ENGINE PERFORMANCE section. Replace ignition coil and/or power transistor if necessary and perform FINAL CHECK in this article. If continuity is not present, repair harness or connectors as necessary.