Code
P0203
ISUZU
P — Powertrain
Injector Circuit - Cylinder 3
Views:
UK: 16
EN: 31
RU: 30
AI status
Completed
Completed
100%
Causes
- Open or short in injector wiring for cylinder 3
- Corroded or loose injector connector
- Faulty fuel injector (coil open/short or internal fault)
- Blown fuse or loss of injector supply voltage
- Poor ground or chassis connection
- Faulty ECM/PCM injector driver
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Rough idle or misfire on cylinder 3
- Loss of power, hesitation or poor acceleration
- Increased fuel consumption and emissions
- Possible hard start or no‑start condition if injector dead
What to check
- Retrieve freeze frame and live data with a scan tool; confirm P0203 and any related codes
- Visually inspect wiring and connector at injector #3 for damage, corrosion or oil contamination
- Check EFI/injector fuse(s) and power/relay for injector supply voltage
- Back-probe injector connector to measure supply voltage and driver signal while cranking or running
- Measure injector coil resistance and compare to service specification
- Wiggle test wiring and connector while monitoring live data or use a scope to watch for intermittent pulses
Signal parameters
- Injector supply (battery) voltage at connector: ~12 V with key ON (verify exact value per vehicle)
- Injector driver output: pulsed to ground (low-side drive) while cranking/running
- Injector coil resistance: check service manual — typical injectors commonly fall within 2–16 Ω depending on type
- Injector pulse width: variable (ms) depending on engine load and RPM; should show pulses when engine cranks/runs
- No continuity between injector driver terminal and battery positive when driver is active (driver pulls to ground)
Diagnostic algorithm
- Connect a scan tool, record codes, freeze frame and live data. Note engine conditions when P0203 set.
- Visually inspect the cylinder 3 injector connector, wiring harness, pin condition and any nearby damaged insulation.
- With ignition ON (engine OFF), verify injector supply voltage at the injector harness pin(s). Confirm good ground paths.
- Measure injector coil resistance at the injector terminals (remove connector). Compare to service spec; replace if open/shorted or out of range.
- Back-probe the injector connector while cranking/running. Confirm the ECM is commanding pulses to the injector (use oscilloscope or scan tool).
- Perform a wiggle test on the wiring and connector while monitoring injector pulse; look for intermittent changes.
- Swap the suspect injector with a known-good injector from another cylinder and re-scan. If the code follows the injector, replace the injector.
- If the code remains on the cylinder 3 circuit after swapping injectors, check continuity and resistance between the injector connector and ECM driver pin. Repair wiring or connector faults.
- Verify fuses/relays and measure for short to power or short to ground in the injector circuit. Repair as needed.
- If wiring, connectors and injector are good, test or replace the ECM/PCM only after confirming driver fault with proper bench or manufacturer diagnostics.
Likely causes
- Damaged harness insulation or pin pushed out at cylinder 3 connector
- Carbon or water corrosion on injector electrical terminals
- Injector coil out of specified resistance range
- Connector pushed off or not fully seated after service
- Blown EFI/injector fuse or relay
- Intermittent ECM output due to internal failure
Fault status
Status
Powertrain control module detected an electrical fault in the fuel injector circuit for cylinder 3. MIL set. Freeze frame and live data stored. Continue diagnostics to isolate wiring, connector, injector or ECM driver fault.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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