P0203 on 2010-2014 Cadillac SRX: Cylinder 3 Injector Circuit Fault Causes and Fixes

What's Unique About the 2010-2014 Cadillac SRX

While P0203 is a standard OBD-II code, the 2010-2014 SRX's 3.0L and 3.6L direct-injection V6 engines have a documented history of fuel system issues. General Motors has issued multiple service bulletins for related problems on these engines that point toward faulty fuel injectors and, critically, wiring harness issues. TSB PIP4924D specifically calls out harness chafing as a cause for P0203, advising technicians to inspect for rub-through against the intake plenum, valve cover bolts, and fuel lines. The primary challenge on this platform is that cylinder 3 is on the rear cylinder bank (firewall side), making access for diagnosis and repair significantly more difficult and labor-intensive than for the front cylinders.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light is on (may flash during severe misfire)
• Engine runs rough or vibrates (misfire).
• Poor acceleration and loss of power.
• Decreased fuel economy.
• Engine may be hard to start or stall
• Smell of unburnt fuel from the exhaust

Most Likely Causes

1. Faulty Cylinder 3 Fuel Injector 🔴 High Probability → Shop Fuel Injector GM's 3.0L and 3.6L V6 direct-injection engines have a known pattern of fuel injector failures, as documented in TSBs for related fuel system codes. The internal coil windings of the injector can fail, creating an open or shorted circuit.
   How to confirm: Measure the injector's internal resistance with a multimeter. A good injector for the 3.6L LFX engine (2012-2014) should measure between 1.2 and 1.8 ohms. A good injector for the 3.0L LF1 engine (2010-2011) should measure approximately 12 ohms. An infinite reading (OL) indicates an open circuit, and a zero or very low reading indicates a short. Both confirm a bad injector. Another definitive method is to swap the injector with one from an adjacent cylinder (e.g., cylinder 1) and see if the code changes to P0201. If the code follows the injector, it is faulty.
   Typical fix: Replace the failed fuel injector. Since accessing the rear bank requires removing the intake manifold, it is highly recommended to replace all three rear injectors (cylinders 1, 3, 5) and the intake manifold gaskets at the same time to save on future labor costs. 🎬 See how to remove the fuel injector rail
   Est. part cost: $50-$180 per injector
2. Wiring Harness or Connector Issue 🟡 Medium Probability GM TSB PIP4924D specifically identifies wiring harness chafing as a common cause for P0203 on this platform. The harness can rub against the intake plenum, valve cover bolts, fuel lines, or the side of the cylinder head, causing wires to break or short out. The connector itself can also become loose, corroded, or have a pin back out.
   How to confirm: Visually inspect the wiring going to the cylinder 3 injector, paying close attention to the chafe points mentioned in TSB PIP4924D. Check that the connector is securely plugged in. Use a noid light to confirm if the PCM is sending a pulse signal to the connector. If the noid light doesn't flash, there is a wiring or PCM issue. A user on YouTube with a similar GM engine found their P0202 was caused by a failed ECM after confirming the wiring was good with a multimeter from the ECM connector to the injector connector.
   Typical fix: Repair the broken or shorted section of wire. If the connector is damaged, replace the connector pigtail. In cases of extensive damage, the entire injector sub-harness may need replacement.
   Est. part cost: $15-$50 for a connector pigtail
3. Faulty Powertrain Control Module (PCM) ⚪ Low Probability → Shop Engine Control Module (ECM)
   How to confirm: This should be the last resort after confirming the injector and wiring are good. If a noid light shows no pulse at the injector connector and a continuity test confirms the wiring from the PCM to the connector is intact, the injector driver circuit inside the PCM has likely failed. A technician can back-probe the ground wire at the injector connector; if a pulsing signal is absent while the engine runs, it points to a PCM driver failure.
   Typical fix: Replace and reprogram the PCM. This requires specialized tools and must be done by a qualified shop or dealer.
   Est. part cost: $300-$800

Diagnosis Steps

1. Read the codes: Use an OBD-II scanner to confirm P0203 and note any other codes present, such as P0303.
2. Visual Inspection: Inspect the wiring harness and electrical connector for cylinder 3. Look for obvious signs of damage, chafing, melting, or corrosion. Pay special attention to areas where the harness may contact the intake manifold, valve covers, or fuel lines, as noted in TSB PIP4924D. Ensure the connector is seated firmly.
3. Check for Signal with a Noid Light: Disconnect the injector and plug a noid light into the connector. Crank the engine. Interpret the results: If the light flashes, the PCM and wiring are sending a signal, suggesting the injector itself is the problem. If it does not flash at all, there is likely an open in the wiring or a failed PCM driver. If it stays on solid, the control wire may be shorted to ground.
4. Test the Injector Resistance: If the noid light flashes, turn the vehicle off. Use a multimeter set to Ohms (Ω) to measure the resistance across the two pins of the fuel injector. For 2012-2014 3.6L LFX engines, the reading should be 1.2-1.8 Ohms. For 2010-2011 3.0L LF1 engines, it should be ~12 Ohms. A reading of 'OL' (Over Limit) means it's open, and a reading near zero means it's shorted. Either indicates a failed injector.
5. Test the Wiring: If the noid light did not flash, check for continuity on the signal wire between the PCM and the injector connector. Also, check for 12V power on the power supply wire at the injector connector with the key in the 'On' position.
6. Swap Components: If you have good access and are unsure, you can swap the cylinder 3 injector with another cylinder's injector (e.g., cylinder 1). Clear the codes, start the engine, and see if the code follows the injector (e.g., changes to P0201). If it does, the injector is confirmed bad. If P0203 returns, the problem is in the wiring or PCM.
7. PCM Diagnosis: If the injector and wiring are confirmed to be good, the final step is to suspect the PCM's injector driver, which requires professional diagnosis.

Parts You'll Likely Need

• Fuel Injector (OEM #12669384 (For 3.6L LFX, supersedes 12638530, 12632255, 12611545)) — This is the most common cause of a P0203 code on this vehicle. The internal electronics of the injector fail, causing an open or shorted circuit.
  Trusted brands: ACDelco (OEM), Bosch, Standard Motor Products
  OEM price range: $100-$180
  Aftermarket price range: $50-$120
• Intake Manifold Gasket Set — To replace the cylinder 3 fuel injector, the upper intake manifold must be removed. The gaskets are single-use and must be replaced to prevent vacuum leaks. 🎬 Watch: Step-by-step fuel injector replacement for the 3.6L engine
  Trusted brands: ACDelco, Fel-Pro, Mahle
  OEM price range: $40-$70
  Aftermarket price range: $20-$40
• Fuel Injector Connector Pigtail — If the plastic connector or its wiring is damaged by heat, vibration, or chafing, replacing the pigtail is the correct repair instead of replacing the entire harness.
  Trusted brands: ACDelco, Dorman
  OEM price range: $25-$50
  Aftermarket price range: $15-$30

Related Codes That Often Appear With This One

• P0303 — P0303 means 'Cylinder 3 Misfire Detected.' A P0203 fault directly causes a P0303 because the electrical issue prevents the injector from delivering fuel, which in turn causes the cylinder to misfire.
• P0201, P0205 — If other injector codes for the same bank (the rear bank includes cylinders 1, 3, and 5) appear, it may suggest a wiring harness issue common to that bank, a problem with the power or ground supply for that group of injectors, or a chafe point affecting multiple wires.

Technical Service Bulletins (TSBs) & Recalls

• PIP4924D: Addresses SES light and misfire with various injector codes (P0201-P0206, etc.) and advises technicians to carefully inspect the fuel injector wiring harness for rubbing through on the intake, valve cover, fuel lines, or cylinder head. This applies to a wide range of 2009-2014 GM vehicles with 3.0L and 3.6L V6 engines.

Platform-Specific Known Issues

• Access to the rear cylinder bank (cylinders 1, 3, 5) is restricted and requires the removal of the upper intake manifold, adding significant labor time and cost to the repair.
• GM Technical Service Bulletin #PIP4924D explicitly directs technicians to check for wiring harness chafing as a cause for P0203. Specific inspection points include where the harness might rub against the intake plenum, valve cover bolts, fuel lines, and the side of the cylinder head.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance (3.6L LFX V6) — expected: 1.2 - 1.8 Ohms. Failure: A reading of OL (open), near 0 (short), or outside the specified range.
• Fuel Injector Resistance (3.0L LF1 V6) — expected: ~12 Ohms. Failure: A reading of OL (open), near 0 (short), or significantly different from 12 Ohms.
• Injector Pulse Width (at normal idle) — expected: 2 - 4 milliseconds (ms). Failure: A value of 0 ms on cylinder 3 while others are pulsing indicates the ECM has shut down the circuit.
• Injector Pulse Width (during cold start) — expected: Nearly double the normal idle pulse width for ~60 seconds.. Failure: This is a normal condition. If the engine smooths out after ~60 seconds as pulse width drops by 50%, no fault is present. This is part of the catalyst heating strategy.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Fuel Injector Balance Test — After confirming the electrical circuit is intact, this test can help identify a mechanically faulty or clogged injector. The tool commands the fuel pump on, then pulses a single injector and measures the drop in fuel rail pressure. A significantly different pressure drop for cylinder 3 compared to others indicates a flow problem with the injector itself.

Wiring & Ground Locations

• G113 — On the left side of the engine block (for 3.0L) or left rear of the block (for 3.6L).. This is a primary engine block ground. The ECM and its driver circuits rely on clean, solid ground connections. A loose or corroded G113 can cause erratic behavior in multiple systems, including unstable operation of the injector driver circuits, potentially triggering a P0203 code.
• Injector Control Circuit — The two wires running from the ECM/PCM main connector to the fuel injector connector for cylinder 3.. One wire provides 12V power (often shared with other injectors on the same bank), and the other is the specific ground-side trigger wire from the ECM. An open or short on either of these wires will cause P0203. The trigger wire for cylinder 3 runs to a dedicated pin on the ECM connector.

Real Owner Repair Stories

• YouTube user diagnosing a 2005 SRX (similar engine/wiring architecture) (2005 Cadillac SRX, 3.6L V6) — P0202 and P0302 codes, cylinder 2 injector not firing.
  ❌ Tried (didn't work) Swapping the #2 injector with another cylinder's injector; the fault code did not move., Visually inspecting the wiring harness loom where it runs under the intake manifold.
  ✅ What actually fixed it The diagnosis concluded the Powertrain Control Module (PCM/ECM) was faulty. The technician performed a continuity test with a multimeter from the PCM connector pin for the injector, through the wiring harness, through the fuel injector itself, and back to the power supply at the fuse block. The resistance measured correctly (~12 ohms), proving the entire circuit outside the PCM was intact. This isolated the failure to the internal injector driver transistor within the PCM, requiring PCM replacement.

OEM Part Supersession History

• 12638530, 12632255, 12611545 → 12669384 — Part revision and improvement by the manufacturer for the 3.6L LFX engine.
  Heads up: Crucially, injectors for the 3.6L LFX engine (2012-2014) have a low resistance (1.2-1.8 ohms) and are NOT interchangeable with injectors for the 3.0L LF1 engine (2010-2011), which have a much higher resistance (~12 ohms). Installing the wrong type will cause an immediate circuit fault or damage the ECM injector driver.

Model Year Variations Within This Range

• 2010-2011 vs 2012-2014: The standard engine changed from the 3.0L LF1 V6 (2010-2011) to the 3.6L LFX V6 (2012-2014). This change affects the fuel injectors, which have different part numbers and, most importantly, different electrical resistance specifications (~12 ohms for LF1 vs. 1.2-1.8 ohms for LFX). The ECMs are also from different families (Bosch vs. Delphi), which may affect advanced diagnostic procedures.