What Does P1240 Mean?
DTC P1240 indicates an open circuit condition in the fuel injector circuit for cylinder 4. The PCM has detected that the injector coil is not drawing current when commanded, meaning there is a break in the electrical path between the PCM driver and the injector. Cylinder 4 will be completely non-functional, causing a dead misfire.
Safety Warning
An open injector circuit results in a dead cylinder, causing significant power loss, rough idle, increased emissions, and unburned oxygen entering the exhaust that can overheat the catalytic converter. Extended driving is not recommended.
Common Causes
30%
Disconnected or damaged fuel injector electrical connector on cylinder 4
25%
Broken wire in the injector harness due to heat damage or fatigue
25%
Failed fuel injector with open coil winding
10%
PCM injector driver pin damage or internal open
10%
Corroded connector pins preventing electrical contact
Diagnostic Steps
1
Verify the cylinder 4 injector connector is fully seated and locked — disconnect and reconnect it to check for spread or corroded pins.
2
Measure resistance across the cylinder 4 injector terminals — an open-circuit reading (OL/infinite) confirms a failed injector coil.
3
If injector resistance is within spec (11-18 ohms), test the harness continuity from the PCM connector pins to the injector connector for both the power and control wires.
4
Use a noid light or injector pulse tester on the cylinder 4 harness connector to verify the PCM is sending an injector pulse signal.
5
Swap the cylinder 4 injector with an adjacent cylinder injector and clear codes to isolate whether the fault is in the injector or the harness.
Estimated Repair Cost
$75 - $400
Parts + labor, varies by vehicle and location
DTC P1240 indicates an open circuit condition in the fuel injector circuit for cylinder 4. The PCM has detected that the injector coil is not drawing current when commanded, meaning there is a break in the electrical path between the PCM driver and the injector. Cylinder 4 will be completely non-fun...
The most common cause of P1240 (Injector Circuit Open Cylinder 4) is: Disconnected or damaged fuel injector electrical connector on cylinder 4
Typical repair costs for P1240 range from $75 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
An open injector circuit results in a dead cylinder, causing significant power loss, rough idle, increased emissions, and unburned oxygen entering the exhaust that can overheat the catalytic converter. Extended driving is not recommended.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1240 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel Injection
Difficulty
Type
Manufacturer
Recommended Tools
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