P0308 on 2007-2009 Saturn Aura: An Impossible Code Explained

What's Unique About the 2007-2009 Saturn AURA

The Saturn Aura shares its GM Epsilon platform with other vehicles like the Pontiac G6 and Chevy Malibu, which also report this same 'ghost code' phenomenon. While misfires on the V6 engines are common (often related to ignition components or timing chains on the 3.6L), the appearance of a P0308 code is unique because it's physically impossible. This immediately shifts the diagnosis away from standard engine components and towards the vehicle's electronic brain or the tools used to read the codes. The provided NHTSA TSB #PIP5628G lists codes P0300-P0308, but this is a generic data-gathering template for technicians to use when diagnosing misfires across many GM vehicles and does not mean the Aura has eight 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
• Code P0308 present in a scan tool reading
• Vehicle may run perfectly fine
• Vehicle may exhibit actual misfire symptoms (rough idle, poor acceleration, shaking, engine stutter) if the P0308 is being displayed alongside other, valid misfire codes (e.g., P0300, P0301-P0306).

Most Likely Causes

1. Scan Tool Error or Incompatibility 🔴 High Probability Not specific to the vehicle, but a common issue with universal, outdated, or low-quality OBD-II scanners that may misinterpret the vehicle's data stream, especially on this GM platform.
   How to confirm: The simplest and most crucial first check is to use a different, high-quality scan tool to read the codes. If the P0308 code does not appear on a second, reliable scanner, the issue was with the initial tool.
   Typical fix: Use a professional-grade or known compatible scan tool for diagnostics. Clear codes with the reliable tool and see if they return.
   Est. part cost: $0
2. Faulty Powertrain Control Module (PCM) 🟡 Medium Probability Electronic modules can fail in unpredictable ways as they age. An internal failure of the PCM, such as a faulty driver circuit for a non-existent cylinder or corrupted memory, can cause it to generate erroneous or impossible trouble codes.
   How to confirm: This is a diagnosis of exclusion. If multiple professional-grade scan tools all report P0308, and all other vehicle systems are functioning correctly, the PCM becomes the primary suspect. A technician may need to check PCM powers, grounds, and data network integrity before condemning the module.
   Typical fix: Replacement of the PCM. The new module will need to be programmed specifically for the vehicle's VIN and options.
   Est. part cost: $200-$500
3. Crankshaft Position Sensor (CKP) System Fault ⚪ Low Probability The PCM uses the CKP sensor to detect misfires by monitoring crankshaft rotational speed. A severe fault in the sensor, its wiring, or a corrupted 'crankshaft position variation relearn' value in the PCM's memory could potentially lead to incorrect misfire calculations. While this usually results in a P0300 or misidentified cylinder, generating an impossible cylinder number is a rare but conceivable outcome of a severe data error. GM's own diagnostic template for misfires includes performing a crank variation learn.
   How to confirm: A technician would use an oscilloscope to check the CKP sensor's signal pattern for glitches or inconsistencies. They would also use a high-level scan tool to attempt a 'crankshaft position variation relearn' procedure.
   Typical fix: If the signal is faulty, replace the Crankshaft Position Sensor. 🎬 Watch: How to replace the crankshaft position sensor on an Aura. If the sensor is good, performing the relearn procedure may resolve the issue.
   Est. part cost: $30-$70

Diagnosis Steps

1. Confirm the code: Use an OBD-II scanner to verify that the code is indeed P0308.
2. Verify with a second scanner: Before any other steps, rescan the vehicle with a different, preferably higher-quality, scan tool. If P0308 does not reappear, the fault lies with the initial scanner. This is the most common resolution.
3. Check for other codes: Note any other codes that are present. If codes for actual cylinders (P0301-P0306) are stored, diagnose those first as a real misfire is occurring. Common causes for real misfires on these engines include ignition coils, spark plugs, and fuel injectors.
4. Inspect for real misfire causes: If drivability issues are present, perform a basic inspection for common misfire sources. On the 3.6L V6, check for oil in the spark plug tubes, which indicates a leaking valve cover or tube seal, a known issue that can foul the plug and coil.
5. Inspect PCM and wiring: Visually inspect the Powertrain Control Module (PCM) and its connectors for any signs of water intrusion, corrosion, or physical damage. Pay close attention to the main engine grounds.
🎬 Watch: A quick and easy way to test for ground faults.
6. Perform a battery and system voltage test: Ensure the battery is healthy and that the charging system is providing stable voltage. Electrical fluctuations can sometimes cause strange module behavior.
7. Consult a professional: If the code persists on multiple scanners and there are no other obvious faults, the vehicle should be taken to a qualified technician. They can perform advanced diagnostics on the Crankshaft Position Sensor signal and the PCM itself.
8. Consider a PCM replacement: If all other possibilities are exhausted by a professional, the PCM is the most likely cause and will likely need to be replaced and programmed.

Parts You'll Likely Need

• Powertrain Control Module (PCM) (OEM #Varies by VIN and engine. Examples: 12618587 (3.6L V6); 12597121 (3.5L V6); 12612397 (2.4L I4). Always verify with VIN.) — A faulty PCM is the most likely vehicle component to cause an impossible 'ghost' code like P0308 when a scan tool error has been ruled out.
  Trusted brands: ACDelco (OEM), CARDONE Reman, Dorman, Flagship One, Flashmasters
  OEM price range: $300-$500
  Aftermarket price range: $200-$400

Related Codes That Often Appear With This One

• P0300 — If the underlying PCM or sensor fault is causing general misfire detection errors, a P0300 (Random/Multiple Misfire) code may appear alongside the erroneous P0308.
• P0301-P0306 — If a real misfire is occurring on one of the actual cylinders, its code may be present. The P0308 may be a symptom of the scan tool's confusion in interpreting the data from the real misfire.
• U-series codes (e.g., U0100) — If the PCM is failing, it may also trigger communication codes (U-codes) indicating a loss of communication with other modules on the vehicle's data network, which is a strong indicator of module failure.
• P1336 — This GM-specific code indicates that the Crankshaft Position (CKP) System Variation has not been learned. This procedure calibrates the PCM to the specific signal of the CKP sensor to allow for accurate misfire detection. If this calibration is corrupt or was not performed after a PCM or sensor replacement, it can cause erratic misfire reporting, potentially including ghost codes like P0308. Performing the 'crank relearn' is a required step after many related repairs.

Technical Service Bulletins (TSBs) & Recalls

• PIP5628G: This Technical Service Bulletin is a generic diagnostic aid for GM technicians. It provides a template of information to collect (e.g., freeze frame data, fuel trims, compression test results) before contacting the Technical Assistance Center (TAC) for help with misfire codes P0300-P0308. Its inclusion of P0308 is for V8-equipped vehicles covered by the bulletin and does not imply the Aura has eight cylinders.

Platform-Specific Known Issues

• 3.6L (LY7) V6 Timing Chain Wear: The 3.6L V6 engine is known for premature timing chain stretching. While this typically sets codes like P0008, P0017, or P0018, the resulting rough running could potentially be misinterpreted by a faulty scanner. If you have a 3.6L and actual misfire symptoms, this is a critical possibility to be aware of.
• Oil in Spark Plug Tubes: A common issue on the V6 engines is the valve cover gasket and/or spark plug tube seals leaking oil into the spark plug wells. This oil can saturate the ignition coil boot and spark plug, causing a real misfire. A user on BobIsTheOilGuy.com reported this exact issue on a 2008 Aura XR causing a misfire that was resolved after cleaning the oil out and replacing the gaskets.

Mechanic-Grade Diagnostic Values

• Crankshaft Position Sensor (CKP) Resistance — expected: 200 to 1,000 ohms. Failure: A reading of 0 ohms indicates a short circuit and requires sensor replacement.
• Engine Block to Battery Negative Ground Voltage Drop (Key On) — expected: Less than 100 millivolts (0.1V). Failure: A reading higher than 100mV, such as the 220mV found in one diagnostic video, indicates high resistance in the ground circuit which can cause numerous, unpredictable electrical problems.

Hidden / Shadow Codes Worth Checking

• P1336: Crankshaft Position (CKP) System Variation Not Learned. This code indicates the PCM has not been calibrated to the specific CKP sensor's signal, which is vital for accurate misfire detection. (see via This code is often set after replacing a PCM or CKP sensor and will be visible with most professional scan tools, including the GM Tech2 or compatible aftermarket scanners.)

Scan Tool Commands That Help

• GM Tech2 / GDS2 / Professional Aftermarket Scanners: Crankshaft Position Variation Learn — This procedure MUST be performed after replacing the PCM, the CKP sensor, or sometimes after clearing a P1336 code. Failure to perform this relearn can cause the PCM to inaccurately calculate misfires, which could potentially manifest as a 'ghost' code like P0308. The procedure involves starting the vehicle, bringing it to operating temperature, and then accelerating to a specific RPM until fuel cut-off, which allows the PCM to learn the sensor's unique signal pattern.

Wiring & Ground Locations

• G105 — For the 3.5L V6, it is located under the left intake manifold on the rear of the cylinder head. For the 3.6L V6, it is at the center rear of the engine. For the 2.4L I4, it is at the left rear of the engine.. This is a primary engine ground. A poor connection here can cause a wide range of sensor and module communication errors, potentially leading to erroneous codes being generated by the PCM.
• G107 — Located on the right front of the engine.. This ground point is used by multiple critical sensors, including the Mass Air Flow (MAF) sensor and is a common ground for the PCM. A corroded or loose G107 ground is a known cause of voltage drops and erratic sensor readings, which can confuse the PCM.
• PCM / ECM Location — Located in the engine compartment on the left side, behind the battery and near the underhood fuse block.. Physical inspection of the module and its connectors is a key diagnostic step. Its location makes it susceptible to damage from battery leaks or physical damage during battery service.
• GMLAN Data Network — This is the vehicle's communication network connecting various modules like the PCM, BCM, and even the radio.. A fault in any module on the network can potentially disrupt communication and cause other modules, like the PCM, to behave erratically. It's important to understand that many components are VIN-locked to the vehicle over this network, including the radio and PCM, and require programming to function if replaced.

Real Owner Repair Stories

• Saturn Forum user 'Dinkster' (2008 Saturn Aura (engine not specified)) — No-crank condition, no communication with ECM via scan tool.
  ❌ Tried (didn't work) Checking fuses, Inspecting underhood fuse block, Repairing a broken wire from unrelated work
  ✅ What actually fixed it The problem was a severely corroded and partially broken common ground point, believed to be G107 or G109. Cleaning and repairing this ground connection resolved the no-communication and no-start issue.

OEM Part Supersession History

• Varies, e.g., 12612384 for 2008 3.5L → Multiple updates, e.g., 12617174, 12617568, 12617630, 12619077, 12622138, 12622141, 12624488, 12629001 — GM frequently updates PCM hardware and software to address bugs, improve performance, and enhance durability. Later part numbers contain the most recent factory updates.
  Heads up: While many part numbers are interchangeable for a given engine, it is critical to program any replacement PCM with the vehicle's specific VIN to ensure all systems function correctly. A used PCM from another vehicle will not work without being reprogrammed.

Model Year Variations Within This Range

• 2007-2009: While the core issue of P0308 being a ghost code is consistent, the specific PCM part numbers changed frequently. For example, a 2007 3.5L V6 used part number 12597121, while a 2008 3.5L used a different series of part numbers. This means a PCM must be sourced based on the exact year, engine, and VIN, not just the model.