How to Check Injector Open Circuit Caused by ECU Fault?

Step 1: Use a decoder to read the fault code, the fault code is P0204: Injector open circuit for the fourth cylinder (physical second cylinder).

Step 2: Check if the injector connector is damaged, corroded, loose, retracted, or if the pins are pushed back; the connector is intact.

Step 3: Disconnect the injector harness interface, use a multimeter to measure the resistance between the injector terminals; normal resistance should be between: 0.2Ω~1Ω, resistance is normal. Continue measuring the resistance between the injector terminals and the vehicle ground; normal resistance should be: OL or infinite, resistance is normal. Determine that the injector is fault-free.

Step 4: Remove the connector, use a multimeter to measure the open circuit voltage; the high-side voltage should be 0, normal should be around 5.6V, suspect a break in the harness.

Step 5: Perform continuity measurements according to the circuit diagram, find the corresponding connector harness for the high side, perform a jumper wire test; the fault persists after the jumper.

Step 6: Both the injector and harness have been checked and found to be fine, but the fault still exists; at this point, we can only suspect whether it is an ECU data issue or an ECU fault.

Step 7: Find a new ECU for replacement testing; the fault is eliminated, and the vehicle runs well.

1. The firing order for a four-stroke inline four-cylinder engine: the firing interval angle should be 720°/4=180°, with four crankshafts arranged in the same plane. There are two possible firing sequences: 1-2-4-3 or 1-3-4-2.

2. The firing order for a four-stroke inline six-cylinder engine: the firing interval angle should be: 720°/6=120°, with six crankshafts arranged in three planes, each plane at an angle of 120°. The first firing order is 1-5-3-6-2-4, which is commonly used in domestic six-cylinder engines. Another firing order is: 1-4-2-6-3-5.