OBD-II Code P0204 — What It Means & How to Fix It

What Does This Error Mean?

P0204 means there is an electrical fault in the fuel injector circuit for cylinder 4. The PCM cannot properly control the injector on that cylinder. Cylinder 4 may be misfiring, causing a rough idle, shaking, and reduced power. The most likely causes are a failed injector, damaged wiring, or a bad connector.

Affected Models

All vehicles 1996+
Common in Honda Civic and Accord four-cylinders
Common in Toyota Corolla and RAV4
Common in Ford Focus and Escape
Common in Chevrolet Sonic and Cruze

Common Causes

Failed fuel injector on cylinder 4 with open or shorted winding
Corroded, damaged, or loose connector at the cylinder 4 injector
Wiring harness damage between the injector and the PCM
Severely clogged injector with resistance outside acceptable range
PCM injector driver failure on the cylinder 4 circuit (rare)

How to Fix It

Identify cylinder 4 on your engine. On a four-cylinder, it's typically the rearmost cylinder. On V6/V8 engines, consult a cylinder diagram for your specific model. Inspect the injector wiring connector first.

Cylinder 4 is often near the firewall on four-cylinder engines, making access slightly more awkward.
Test injector resistance with a multimeter. Unplug the injector connector and probe both terminals with the ohms setting. Healthy injectors typically read 11-17 ohms. Out-of-range readings mean the injector has failed.

Zero ohms = shorted coil; infinite ohms = open coil. Either condition means replacement is needed.
Trace the injector wiring harness from the connector toward the firewall. Check for damaged insulation, pinched wires, or corroded connectors along the route. Repair any damage found before replacing parts.

On rear-cylinder injectors, wiring can be routed near the firewall where heat and vibration cause wear.
Perform the swap test — move the cylinder 4 injector to another cylinder and put a known-good injector on cylinder 4. Clear the code and drive. If the fault follows the injector, it's bad. If it stays on cylinder 4, the wiring is the problem.

The swap test is definitive and requires no special tools beyond a basic socket set.
Install a new injector with a fresh O-ring. Lightly lubricate the O-ring with clean engine oil before installation. Clear all codes, test drive, and verify no misfires using a scan tool's misfire counter.

If the vehicle has over 120,000 miles, consider replacing all injectors as a set for reliability.

When to Call a Professional

If the injector and wiring both test fine, have a professional diagnose the PCM driver circuit. A technician uses a noid light and an oscilloscope to verify signal delivery to the injector. This pinpoints whether the fault is internal to the PCM. Diagnosis typically costs $80-$130. Injector replacement is $150-$400 depending on access and vehicle.

Frequently Asked Questions

Can a dirty injector cause P0204?

Possibly, though it's less common than a failed or wiring-related fault. A severely clogged injector can have resistance outside normal range. However, most clogged injectors still have normal resistance — they just don't flow correctly. If resistance tests fine but the injector still misfires, try professional ultrasonic cleaning before replacement.

What's the difference between P0204 and P0304?

P0204 is an electrical fault in the injector circuit. P0304 is a detected misfire on cylinder 4, regardless of cause. You can have P0304 from a bad spark plug, bad coil, or low compression — none of which are P0204. If both codes appear together, the injector circuit is very likely the root cause.

How long can I drive with P0204 before causing damage?

Not long. A dead cylinder sends raw fuel into the exhaust system. This fuel can quickly overheat and destroy the catalytic converter. Cat replacement can cost $500-$2,000+. Fix P0204 promptly to avoid a much bigger repair bill.