What Does P1203 Mean?
P1203 indicates that the fuel injector circuit for cylinder #3 has an open or short circuit condition. The ECM has detected an electrical fault in the wiring or connector feeding the #3 injector, preventing proper fuel delivery to that cylinder. This will cause a misfire on cylinder 3, rough idle, reduced power, and increased emissions.
Common Causes
30%
Failed or internally shorted fuel injector on cylinder 3
25%
Damaged or corroded wiring in the injector harness
20%
Loose, corroded, or disconnected injector connector
15%
Faulty injector driver circuit in the ECM/PCM
10%
Chafed wiring causing short to ground or power
Diagnostic Steps
1
Read freeze frame data and note engine RPM, load, and coolant temperature at the time of the fault to understand operating conditions.
2
Measure the resistance of the cylinder 3 fuel injector with a multimeter (typical spec: 11-18 ohms for high-impedance injectors). Compare against manufacturer specs and other cylinders.
3
Inspect the injector connector at cylinder 3 for corrosion, bent pins, loose fit, or moisture intrusion. Wiggle test the connector while monitoring for intermittent faults.
4
Perform a wiring continuity and short-to-ground test on both injector circuit wires from the ECM connector back to the injector connector.
5
Use a noid light or oscilloscope to verify the ECM is sending a proper injector pulse signal to the cylinder 3 injector driver output.
6
If all wiring and the injector test good, swap the cylinder 3 injector with an adjacent cylinder and clear codes to determine if the fault follows the injector or stays at cylinder 3.
Estimated Repair Cost
$150 - $600
Parts + labor, varies by vehicle and location
P1203 indicates that the fuel injector circuit for cylinder #3 has an open or short circuit condition. The ECM has detected an electrical fault in the wiring or connector feeding the #3 injector, preventing proper fuel delivery to that cylinder. This will cause a misfire on cylinder 3, rough idle, r...
The most common cause of P1203 (Injector Circuit Open / Shorted - Cylinder #3) is: Failed or internally shorted fuel injector on cylinder 3
Typical repair costs for P1203 range from $150 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A dead cylinder reduces power output and may cause catalytic converter damage from unburned fuel. Extended driving can overheat the catalyst, potentially creating a fire risk. Vehicle may stall unexpectedly in traffic.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1203 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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