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P0203 means the PCM sees an open (broken) circuit on injector 3 - no injector pulse is being delivered. Cylinder 3 will not fire, causing a rough idle and likely P0303 misfire code as well. Check injector resistance first (12–16 ohms is typical) before assuming a wiring fault. See top-rated scanners on Amazon ↗
🗺️ Where Is the Problem?
Blueprint view - P0203 fault at fuel injector for cylinder 3 - open circuit, no fuel delivery
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0203 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
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🎯 Top Causes & Probability
50%
#1 - Most Likely
Failed Cylinder 3 Injector (Open Coil)
The injector's internal solenoid coil has broken, creating an open circuit that the PCM detects. Measure resistance across the injector terminals - typical spec is 12–16 ohms for high-impedance injectors. An open reading (infinite resistance / OL) confirms a dead injector.
🔩 Part
$30–$150
👨🔧 Labor
$80–$200
⚡ DIY Difficulty
Medium
30%
#2 - Check First
Broken Wiring to Injector 3
A broken wire in the injector harness - often at a flex point near the valve cover or due to heat damage near the exhaust - creates the open circuit. If resistance is good at the injector but bad at the PCM connector, the wire is broken somewhere in between.
🔩 Part
$5–$30
👨🔧 Labor
$80–$200
⚡ DIY Difficulty
Medium
12%
#3 - Less Common
Corroded Injector 3 Connector
Green or white corrosion inside the injector electrical connector causes high resistance or an outright open in the circuit. Remove the connector and inspect for corrosion - cleaning with electrical contact cleaner and a small brush sometimes resolves the code without replacing anything.
🔩 Part
$5–$30
👨🔧 Labor
$40–$80
⚡ DIY Difficulty
Easy
8%
#4 -
PCM Injector 3 Driver Fault
The PCM's internal driver circuit for injector 3 has failed. This is rare and is a diagnosis of exclusion. Confirm by testing injector 3 resistance at the injector and measuring voltage at the PCM connector - if everything checks out externally, the PCM may be at fault.
🔩 Part
$200–$800
👨🔧 Labor
$100–$200
⚡ DIY Difficulty
Hard
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Measure Injector 3 Resistance - Disconnect the connector from injector 3 and measure resistance across its two terminals with a DVOM. Spec is typically 12–16 ohms. An "OL" (open loop) reading confirms the injector coil is broken and needs replacement.
- Inspect Connector for Corrosion - With the connector off, visually inspect for green or white corrosion, bent pins, or moisture. Spray with electrical contact cleaner, reconnect, clear codes and retest before assuming the injector is bad.
📍 Find a Trusted Shop Near You
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