Draft guidance: awaiting Claude spot-check, qualified-mechanic review and named-editor approval. Do not use a fault code alone to replace parts.
P0204: Injector circuit fault, cylinder 4
The engine control unit has found an electrical problem in the circuit operating cylinder 4's fuel injector.
What P0204 means
The engine control unit has found an electrical problem in the circuit operating cylinder 4's fuel injector. It identifies the affected control circuit, not necessarily a dirty injector and not automatically a failed engine control unit.
Can I still drive?
Treat P0204 as urgent. Incorrect fuelling on one cylinder can cause misfiring, stalling, reduced power and catalytic-converter damage. Consider only a short, low-load trip to a nearby garage when the warning light is steady, the engine remains stable and there is no leak, fuel smell, smoke or material loss of power. Stop and recover the vehicle for a flashing warning light, severe vibration, repeated stalling, substantial power loss or any indication that fuel is escaping.
Symptoms
- Engine-management light
- Rough running or vibration
- Hesitation and weak acceleration
- A cylinder 4 misfire code stored alongside P0204
- Hard starting or stalling
- Increased fuel use
- Possible fuel smell or exhaust smoke
- Heat- or vibration-related intermittent symptoms
Common causes
- Damaged, loose or corroded cylinder 4 injector connector
- Open circuit, short circuit or high resistance in the injector loom
- Loom chafing against an engine cover, bracket or other hard edge
- Electrically failed injector
- Shared injector fuse, relay, supply or earth fault
- Backed-out or damaged terminal at an intermediate connector
- Engine-control-unit driver fault, less commonly
Safe first checks
- Save all codes and freeze-frame data; note whether other P020x or supply-voltage codes are present.
- Check the manufacturer's cylinder layout before deciding which injector is number
- 3. With the ignition off and engine cold, inspect the accessible connector and loom for broken clips, rubbing, corrosion, oil or recent disturbance.
- Check handbook-listed fuses only, without substituting a higher rating.
- Do not restart the engine if fuel is visible or strongly smelt; keep flames, sparks and smoking materials away.
- Leave resistance, current, continuity and actuator testing to a suitably equipped technician, especially on direct-injection systems.
Typical UK fix cost
A reasonable provisional range is £90–£250 for diagnosis and a minor wiring or connector repair, £180–£450 for many conventional petrol injectors, or £300–£800 per injector for direct-injection petrol or common-rail diesel applications where fitting, seals and coding are included. Extensive harness repair, a seized injector or control-unit work may exceed £1,000. These figures are broad budgeting estimates, not quotes, and require a current vehicle-specific human price check.
Related models
This is a generic OBD-II code used across many makes and models. The exact test thresholds, component layout and repair route vary by engine and manufacturer, so check vehicle-specific technical information before ordering parts.
Related fault codes
Sources
- Volkswagen technical tip — injector circuit faults P0201–P0204 (NHTSA PDF)
- Delphi Technologies — fuel-system diagnostic guidance
- RAC — car diagnostics and typical UK diagnostic pricing
A diagnostic trouble code identifies a system or circuit to investigate. It does not prove that a named part has failed. Preserve freeze-frame data and seek a vehicle-specific diagnosis before clearing the code.