P21EE — Cylinder 10 Injector B Circuit Low

Diagnostic algorithm

1. Verify the code with a scan tool and record freeze-frame data and any other related codes.
2. Perform a careful visual inspection of the wiring and connector for cylinder 10 Injector B. Look for heat damage, pin corrosion, broken wires, or signs of aftermarket modifications.
3. Clear the code and perform a key-on/run test to see if it returns; note when it occurs (start, idle, under load).
4. With ignition OFF, disconnect the injector connector and measure injector coil resistance across the injector terminals; compare to specification. If out of range, bench-test or replace the injector.
5. Check for unintended continuity between the injector control wire and ground (short to ground) and between the control wire and battery positive (short to power) with harness disconnected at the injector.
6. Backprobe harness at the connector with key ON and engine cranking/running: verify injector supply (battery feed) and that the ECM is commanding the injector (driver pulses to ground). Use an oscilloscope for waveform verification if available.
7. Swap the suspect injector with a known-good injector from another cylinder (if practical). If the code moves to the other cylinder, the injector is confirmed faulty. If the code stays on cylinder 10, suspect wiring/ECM.
8. Inspect and test ECM ground points and related power supplies. Check connector pin continuity from injector connector back to the ECM.
9. If wiring and injector test OK and code persists, test the ECM injector driver output per manufacturer procedures; replace ECM only after confirming driver fault.
10. After repair, clear codes and perform a road test to confirm the fault does not return; re-scan and verify correct engine operation.