P0203 Injector Circuit Malfunction (Cylinder 3) — Causes & Fix
Updated for 2026 diagnostics & repair guidance
P0203 at a Glance
What it means
The ECU has detected a fault in the fuel injector electrical circuit for cylinder 3.
Most common cause
Faulty injector, wiring damage, or ECU driver fault.
Severity
Moderate to serious — causes misfire on cylinder 3.
Can you drive?
Short distances only. Prolonged driving risks DPF and catalytic converter damage.
Typical repair cost
£100-£350 for injector replacement; £40-£100 for wiring repair.
What Does P0203 Mean?
P0203 indicates the ECU has detected an electrical fault in the fuel injector circuit for cylinder 3. Cylinder 3 is the third from the timing belt end on inline engines. The diagnostic and repair approach is the same as P0201/P0202.
Common Causes
Injector-Related Causes
Failed injector solenoid
The cylinder 3 injector solenoid has failed electrically.
Other Possible Causes
Damaged wiring to injector
Wiring harness damage to cylinder 3 injector.
Corroded injector connector
Connector corrosion on cylinder 3 injector.
ECU injector driver fault
Cylinder 3 driver transistor failure in ECU.
Symptoms Drivers Notice
- Engine misfires and runs rough at idle
- Vibration through steering wheel and cabin
- Loss of power during acceleration
- Engine management light on
- Increased fuel consumption
- Exhaust smoke (white or black)
Vehicles Commonly Affected
Can You Still Drive with P0203?
Short distances at low load are safe. Diagnose within 48 hours to prevent DPF contamination and oil dilution.
How Mechanics Diagnose P0203
- 1
Read and confirm fault codes
Confirm P0203 targets cylinder 3.
- 2
Inspect wiring and connector
Check cylinder 3 injector wiring for damage.
- 3
Measure injector resistance
Test solenoid resistance (spec: 0.3-1.2 ohms).
- 4
Perform leak-off test
Check all injectors for mechanical wear.
- 5
Swap test
Swap cylinder 3 injector to confirm fault source.
Repair Solutions & Costs
Replace the injector
Remanufactured injector replacement.
Repair the wiring
Repair damaged wiring.
Clean or replace connector
Clean or replace corroded connector.
When Injector Replacement Is Required
Replace when solenoid resistance is out of spec, leak-off confirms excessive return, or swap test proves fault follows injector.
Compatible Injector Part Numbers
5 injectors compatible with engines affected by P0203.
Cross Reference Numbers
OEM and alternative part numbers for injectors affected by P0203.
Affected Vehicle & Engine Combinations
Need a Replacement Injector?
UK-tested remanufactured injectors with 12-month warranty. Search by engine code or vehicle registration.
Need it fast? Same-day dispatch on in-stock injectors.
Order before 2pm for next working day delivery (UK mainland). Call us on 020 3355 6581.
Engine-Specific Guides
Frequently Asked Questions
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Need Help With P0203?
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