What Does P1204 Mean?
P1204 indicates an open or short circuit condition in the fuel injector circuit for cylinder #4. The ECM has detected that the electrical signal to the #4 injector is not within expected parameters, meaning the injector may not be firing correctly or at all. This results in a cylinder 4 misfire, rough running, and potential catalytic converter damage from unburned fuel.
Common Causes
30%
Defective fuel injector on cylinder 4 with internal open or short
25%
Corroded or damaged wiring in the injector harness to cylinder 4
20%
Poor electrical connection at the injector connector
15%
ECM injector driver circuit failure for cylinder 4
10%
Wiring harness rubbing against engine components causing intermittent short
Diagnostic Steps
1
Retrieve freeze frame data to identify operating conditions when the fault occurred, noting RPM, engine load, and temperature.
2
Measure the resistance of the cylinder 4 injector (typical: 11-18 ohms). Compare to adjacent cylinders and manufacturer specification.
3
Visually inspect the cylinder 4 injector connector for corrosion, moisture, bent terminals, or signs of heat damage.
4
Test wiring continuity and insulation from the ECM injector driver pin to the cylinder 4 injector connector, checking for opens and shorts to ground or B+.
5
Use a noid light at the cylinder 4 injector connector to verify the ECM is commanding the injector to fire.
6
Swap the cylinder 4 injector with a known-good cylinder and monitor if the code follows the injector to confirm a failed component.
Estimated Repair Cost
$150 - $600
Parts + labor, varies by vehicle and location
P1204 indicates an open or short circuit condition in the fuel injector circuit for cylinder #4. The ECM has detected that the electrical signal to the #4 injector is not within expected parameters, meaning the injector may not be firing correctly or at all. This results in a cylinder 4 misfire, rou...
The most common cause of P1204 (Injector Circuit Open / Shorted - Cylinder #4) is: Defective fuel injector on cylinder 4 with internal open or short
Typical repair costs for P1204 range from $150 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Running on a dead cylinder reduces available power which can be dangerous during passing or merging. Persistent misfires dump raw fuel into the exhaust, risking catalytic converter overheating and potential fire hazard.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1204 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel Injection System
Difficulty
Type
Manufacturer
Recommended Tools
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