P0204
Injector Circuit/Open - Cylinder 4
The appearance of the standard OBD2 trouble fault code P0204 is an indicator that your vehicle ECU triggered a threshold alert for "Injector Circuit/Open - Cylinder 4". Understanding the root component breakdown helps avoid expensive diagnostic fees.
Driver's Summary
A P0204 fault code points directly to a problem with injector circuit/open - cylinder 4 that the ECM has confirmed over multiple drive cycles. On the road, this usually shows up as misfire, rich or lean exhaust smell, loss of power. This is not a code to ignore — the underlying fault can rapidly worsen and lead to costly repairs if driving continues.
Symptoms
Misfire, rich or lean exhaust smell, loss of power
Common Causes
- Defective Cylinder 4 fuel injector
- Open ground circuit to injector
- Failed PCM driver
- Corrosion in wiring harness
How to Fix
- 1 Replace Cylinder 4 injector
- 2 Trace and repair ground wire
- 3 Test PCM
- 4 Replace affected wiring section
Technical Explanation
The PCM triggers P0204 after its internal monitoring routine detects that a specific circuit or sensor has exceeded its acceptable operating range. The PCM monitors crankshaft rotational velocity via the CKP sensor at a resolution of individual tooth gaps on the reluctor ring. A combustion event in each cylinder produces a measurable acceleration spike; its absence or weakness is flagged as a misfire event within a 200-revolution or 1000-revolution test window. Once confirmed, the code is stored as a permanent DTC and the MIL is activated. The freeze frame snapshot — recording RPM, load, coolant temperature, and fuel trim at fault detection — is also saved and is critical for accurate diagnosis.
Is It Safe to Drive?
An active P0204 code under high-severity conditions means the affected system is operating outside safe parameters. Continued driving — especially under load or at highway speeds — significantly increases the risk of secondary damage to components like open ground circuit to injector.
Mechanic's Pro Tip
When diagnosing P0204, always test fuel volume delivery in addition to static pressure — a pump that holds pressure at idle but delivers insufficient volume under load will cause the fault only during acceleration or high demand, making it difficult to replicate in the driveway. Use a fuel pressure gauge with a volume outlet port: a healthy pump should deliver at least 1 liter per minute. Replace the fuel filter first; it's the cheapest test and solves the fault in a significant percentage of cases.
Fuel injector: $150 - $400