P0203 - Cylinder 3 Fuel Injector
System
Powertrain (Engine & Gearbox)
Technical Description
The control module has detected a fault in the Cylinder 3 Fuel Injector (P0203). The module sees no circuit at all — broken wire, backed-out pin, or a failed sensor. The fault is isolated to cylinder 3, positioned in the central engine thermal core. This directly impacts individual cylinder volumetric efficiency, firing synchronization, and dedicated harness branch loading.
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Cylinder 3 Injector – Coil Resistance | Resistance (Ω) | 11.5 - 15.5 Ω (port) / 0.5 - 3.0 Ω (direct injection) | Connector disconnected at 20°C (cylinder 3) |
| Cylinder 3 Injector – Injection Pulse at 360° crank angle | Signal (ms) | 2.5 - 4.5 ms idle / 1.5 - 20 ms under load | Engine running |
| Cylinder 3 Injector – Supply Voltage | Voltage (V) | 11.8 - 14.4 V (port) / up to 65 - 90 V boost (direct) | Ignition ON / engine running |
Connector disconnected at 20°C (cylinder 3)
Engine running
Ignition ON / engine running
Oscilloscope Waveform Analysis
1 ms/div, 20 V/divPossible Causes
Open circuit, damaged wiring harness, or disconnected plug at Cylinder 3 Fuel Injector
Thermal core hotspot (cylinder 3):Peak engine operating temperatures due to Siamese exhaust port layout and restricted coolant jacket passages.
Exhaust radiant heat embrittlement:Central manifold radiant heat degradation causing dielectric breakdown of cylinder 3 harness insulation.
Channel A:Verify dedicated wiring pins and signal pair for circuit A against the schematic.
Chafed or pinched wiring harness along the signal path to Cylinder 3 Fuel Injector
Internal mechanical wear or carbon deposits inside Cylinder 3 Fuel Injector
Defective internal output driver or reference circuit in the control module for Cylinder 3 Fuel Injector
Symptoms
Recommended Solution
Compare signal voltage and resistance between circuit A and companion circuit B at module connector.
Swap component on cylinder 3 over to cylinder 4 and clear DTCs to confirm if fault follows.
Measure component internal coil resistance both cold (20°C) and immediately after hot soak (95°C) to catch thermal open circuit.
Verify continuity (< 0.5 Ω) on the signal wire between the component plug and the ECM header connector.
Verify loaded supply voltage and harness terminal pins at Cylinder 3 Fuel Injector.
Check circuit continuity and ground-side voltage drop (< 0.05 V) for Cylinder 3 Fuel Injector.
Perform fuel rail pressure-drop / balance test to identify leaking, stuck, or clogged injectors.
Mechanic's Tip
Pro-tip for cylinder 3: Cylinder 3 is the thermal core of the engine block. A component testing within spec cold (20°C) may only fail once thermal saturation occurs (95°C).