EN

Severity: Moderate Code type: Generic (all makes)

P0204 Code: Injector Circuit / Open – Cylinder 4

The circuit to injector 4 is open or out of range; on most transverse engines that's the transmission end.

Safety first · Consult a professional

  • Fuel vapor is flammable. No smoking or open flames; work outdoors and fix fuel leaks before driving.

At a glance

Severity: 3/5 – Moderate3/5

Severity: Moderate

Meaning
Injector Circuit / Open – Cylinder 4
System
Fuel & Air Metering · Powertrain
Safe to drive?
With caution
Typical repair cost
$0–$1,500
DIY difficulty
Moderate

P0204 sets when the ECU's monitoring of the injector 4 circuit finds no current, or no switch-off spike, where it expects them. That makes it a wiring, connector, coil or driver fault rather than a dirty injector. On transverse four-cylinder engines, cylinder 4 is the one at the transmission end, usually on the driver's side. That corner of the engine bay is crowded: the battery, the air filter box and on many cars the ECU itself sit close by, and the injector sub-harness often joins the main engine harness there through an inline connector. Battery acid vapor, water running off the cowl, air box removal and the engine rocking on its mounts all take a toll on wiring at this end. Transmission and clutch jobs, where the engine is lowered or tilted, are another classic moment for this plug to be stretched or left off.

Can I keep driving? Drivable for a short, gentle trip with one cylinder dead. Avoid highway speeds and towing, and stop if the check engine light begins to flash.

How to read P0204

How to read P0204P10223044
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 2 Fuel & air (injector circuit)
  4. 04 Specific fault

Symptoms

  • Steady three-cylinder shake at idle
  • Check engine light on, often together with P0304
  • Weak acceleration, especially uphill
  • Code that started after transmission, clutch, battery or air box work
  • Misfire that comes and goes over bumps or when the engine rocks on its mounts

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Corroded or loose inline connector where the injector sub-harness joins the engine harness near the transmission end 22%
  2. Open coil in injector 4 22%
  3. Harness stretched or pinched during transmission, clutch or engine mount work 16%
  4. Corrosion from battery acid vapor or water from a blocked cowl drain 14%
  5. Heat damage from a nearby EGR valve or pipe on engines that route it at this end 10%
  6. ECU driver for injector 4 failed, or on direct injection the high-side driver it shares with injector 1 10%
  7. Injector 4 connector knocked off while the air box or battery tray was out 6%

Diagnosis step by step

Diagnostic flow: P02041Start at the battery corner2Inspect the inline harness connector3Measure injector 4 for its type4Load-test the feed5Swap injector 4 with injector 36Check the control wire to the ECU

  1. Start at the battery corner

    Clean the battery terminals and check the ground straps to the body and transmission. Then look closely at the injector harness where it passes the battery tray, air box and ECU: white crust, green pins and brittle insulation are typical of acid vapor damage.

    Tools: Flashlight, Gloves

  2. Inspect the inline harness connector

    Many engines join the injector sub-harness to the main harness through a multi-pin connector near the transmission end or the ECU. Unplug it, look for water, corrosion and pushed-back pins, and reseat it firmly. One bad pin there can take out a single injector.

    Tools: Flashlight, Screwdriver

  3. Measure injector 4 for its type

    High-impedance port injectors read about 12 to 16 ohms; gasoline direct injectors roughly 1 to 3 ohms; diesel solenoid injectors under 1 ohm. Piezo diesel injectors show very high resistance and must be tested with a scan tool instead. Compare with injector 3 before deciding.

    Tools: Multimeter

  4. Load-test the feed

    A voltmeter can show a full 12 V through a corroded wire that collapses as soon as current flows. Connect a test light between the injector 4 feed pin and ground: it should glow brightly with the key on. A dim light means resistance upstream, often at the inline connector.

    Tools: Multimeter, Flashlight

  5. Swap injector 4 with injector 3

    If the injector reads borderline, trade it with injector 3 using new seals, clear the code and drive. P0203 appearing convicts the injector; P0204 staying means the circuit. Cylinder 3 is the right partner because it runs on the 2/3 driver pair, not the 1/4 pair that many direct-injection ECUs share.

    Tools: Screwdriver, OBD-II scanner

  6. Check the control wire to the ECU

    Battery disconnected, ECU unplugged: the injector 4 control wire should measure under 1 ohm from connector to ECU pin and show no continuity to ground. Flex the harness at the engine mount and battery tray while watching the meter to catch a break that only opens with movement.

    Tools: Multimeter

Where the parts are

Ignition: coils and spark plugs per cylinder – P02041234567
Ignition: coils and spark plugs per cylinder
  1. 1Ignition coil
  2. 2Spark plug
  3. 3Fuel injector
  4. 4Camshaft sensor
  5. 5Crankshaft sensor
  6. 6Engine computer (ECM)
  7. 7Intake manifold

Repair options & costs

RepairDIY?Estimated cost
Clean and reseal the inline injector harness connector Yes $30–$200
Repair harness damaged by acid, water or heat No $120–$400
Replace injector 4 (port or direct injection) No $150–$800
Clear the cowl drain and protect the harness Yes $0–$120
Repair the ECU driver or replace the ECU No $500–$1,500

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Emissions / smog test impact

Will fail

An active P0204 with the check engine light on fails an OBD-II smog check. Repair the circuit, confirm the misfire is gone and drive a few days so every readiness monitor completes before the test.

Frequently asked questions

P0204 showed up after a clutch replacement. Could the job have caused it?

Quite possibly. The transmission end of the engine is lowered or tilted during a clutch job, which can stretch the injector harness, pull a connector half off or trap wiring under a bracket. Check that end of the harness first.

Can a leaking battery cause P0204?

Indirectly, yes. Acid vapor from a battery near the injector harness corrodes terminals and insulation over time. Low voltage from a weak battery usually sets several codes at once, while acid damage tends to hit just the circuits routed past the battery tray.

Can I test a diesel piezo injector with a multimeter?

Not in a meaningful way. Piezo stacks behave like capacitors and read very high resistance even when healthy. Use a scan tool's injector tests, or have a diesel specialist check them.

Is cylinder 4 always the one next to the transmission?

On most transverse four-cylinders, yes. Longitudinal engines put it at the rear near the firewall. A few European makers number from the flywheel end instead, so always confirm the numbering for your engine.

Sources