P0720 on 2007-2009 Saturn Aura: Output Speed Sensor Causes and Fixes

What's Unique About the 2007-2009 Saturn Aura

The Saturn Aura from this period used two primary automatic transmissions: the 4-speed 4T45-E for four-cylinder models and the 6-speed 6T70 for V6 models. While the P0720 code's meaning is the same for both, the physical location of the Output Speed Sensor and potential failure points differ significantly. On the 4T45-E, the OSS is typically an externally mounted sensor that is easier to access. On the 6T70, the sensor is located inside the transmission, requiring removal of the side cover for replacement. Furthermore, the 6T70 transmission is notorious for a specific internal failure of the 3-5-R wave plate, which can generate metallic debris that damages the OSS, leading to a P0720 code.

Symptoms You May Notice

• Check Engine Light is on
• Erratic, harsh, or delayed gear shifting
• Speedometer works incorrectly or not at all
• Vehicle may stall when coming to a stop
• Cruise control may not function
• Decreased fuel economy
• Transmission may enter a "limp mode," often stuck in one gear
• ABS or Traction Control light may illuminate

Most Likely Causes

1. Faulty Output Speed Sensor (OSS) 🔴 High Probability Sensors are electronic components that can fail over time due to heat cycles and vibration. On 6T70 models, debris from internal component wear, particularly the 3-5-R wave plate, can physically damage or contaminate the magnetic sensor.
   How to confirm: Test the sensor's resistance with a multimeter or observe its signal output on an oscilloscope while rotating the wheels. An out-of-spec resistance reading or an erratic/absent signal confirms failure. 🎬 Watch: How to diagnose and fix a P0720 code Upon removal, inspect the sensor's magnetic tip for metallic shavings.
   Typical fix: Replace the Output Speed Sensor. On 4T45-E (4-cyl) it is external. On 6T70 (V6) it is internal.
   Est. part cost: $25-$70
2. Damaged Wiring or Connectors 🟡 Medium Probability The wiring harness leading to the transmission can be exposed to road debris, heat, and moisture, leading to corrosion, chafing, or broken wires, particularly at the connector pigtail.
   How to confirm: Visually inspect the wiring harness and connector for any signs of damage, corrosion, or loose pins. Perform a continuity test on the wires between the sensor and the TCM.
   Typical fix: Repair the damaged section of the wiring harness or replace the connector pigtail.
   Est. part cost: $10-$40
3. Low or Contaminated Transmission Fluid ⚪ Low Probability → Shop Transmission Assembly On V6 models with the 6T70 transmission, a common failure of the 3-5-R wave plate releases metallic debris into the fluid. This debris can interfere with the magnetic OSS, causing an incorrect signal and the P0720 code.
   How to confirm: Check the transmission fluid level and condition. If the fluid is dark, smells burnt, or contains visible shiny metal particles, it indicates a significant internal problem.
   Typical fix: Perform a transmission fluid and filter change. If significant metal is present, a transmission rebuild to replace the failed components (like the wave plate) is required.
   Est. part cost: $80-$200 for fluid and filter

Rare But Worth Checking

• Faulty Transmission Control Module (TCM) or Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) This is an uncommon cause. All other possibilities, especially the sensor and wiring, should be exhaustively ruled out before considering module replacement, as it is expensive and often requires programming.
• Internal Transmission Mechanical Failure (6T70 V6 Models): → Shop Transmission Assembly The P0720 code can be a secondary symptom of the well-documented 3-5-R wave plate failure in the 6T70 transmission. The metal fragments from the broken plate contaminate the fluid and can damage the OSS. This issue was so common that GM issued a special coverage program (14404A) extending the warranty, though most vehicles are now past the coverage period. This is a major repair requiring a transmission rebuild.

Diagnosis Steps

1. Retrieve all stored DTCs with an OBD-II scanner to confirm P0720 and check for any related codes.
2. Check the level and condition of the automatic transmission fluid. Look carefully for a burnt smell or the presence of metallic particles, especially on V6 models.
3. Perform a thorough visual inspection of the Output Speed Sensor's wiring harness and connector. Look for any signs of chafing, corrosion, or loose connections.
4. If the wiring appears intact, test the sensor itself. Disconnect the sensor and measure its internal resistance with a multimeter, comparing the reading to the manufacturer's specifications.
5. For a more definitive test, use a multimeter set to AC volts or an oscilloscope to monitor the sensor's signal while safely spinning the drive wheels (with the vehicle securely on jack stands). A signal that is erratic or absent indicates a bad sensor.
6. If replacing the sensor, inspect the magnetic tip of the old sensor for metal debris. A significant amount of shavings points to a more serious internal transmission problem that must be addressed.
7. If the sensor produces a good signal at the connector, the problem lies in the wiring to the TCM or the TCM itself. Perform continuity and ground checks on the wiring harness between the sensor and the control module.
8. If the sensor and wiring are confirmed to be good, the final step would be to diagnose the Transmission Control Module, which is best left to a professional.

Parts You'll Likely Need

• Automatic Transmission Output Speed Sensor (OEM #ACDelco 24262388 (For 6T70 V6 models)) — This sensor is the most common failure point for a P0720 code.
  Trusted brands: ACDelco, Delphi, Standard Motor Products, NGK
  OEM price range: $35-$80
  Aftermarket price range: $25-$60

Related Codes That Often Appear With This One

• P0700 — P0700 is a generic code indicating that the Transmission Control Module (TCM) has stored a fault. It frequently appears alongside more specific transmission codes like P0720.
• P0500 — P0500 relates to the Vehicle Speed Sensor (VSS) circuit. On many vehicles, the OSS data is used as the VSS input, so a fault in the OSS circuit can trigger both codes.
• P0721, P0722, P0723 — These are related codes that point to more specific faults within the Output Speed Sensor circuit, such as range/performance issues (P0721), no signal (P0722), or an intermittent signal (P0723).
• P0776, P0842 — On 6T70 models, these codes related to pressure control solenoids and switches can appear alongside P0720 when the root cause is a broken 3-5-R wave plate generating debris.

Technical Service Bulletins (TSBs) & Recalls

• GM Special Coverage 14404A / TSB 09-07-30-012F: Addresses the fractured 🎬 See how a broken wave plate damages this transmission 3-5-R wave plate in 6T70/6T75 transmissions, which is a primary cause of debris-related sensor failures. This extended coverage to 10 years/120,000 miles, but most vehicles have aged out.

Platform-Specific Known Issues

• Location Difference: The OSS on the 4-speed 4T45-E (I4 engines) is external and relatively easy to replace. On the 6-speed 6T70 (V6 engines), the sensor is internal, requiring removal of the transmission side cover, which is significantly more labor-intensive.
• 6T70 Wave Plate Failure: V6 models are highly susceptible to a broken 3-5-R wave plate. This is a known defect acknowledged by GM in TSB 14404A. The resulting metal debris often causes the P0720 code by damaging the OSS. If metal is found in the pan, simply replacing the sensor is not a complete fix; the transmission needs to be disassembled to replace the wave plate and clean out all debris.

Mechanic-Grade Diagnostic Values

• Output Speed Sensor (OSS) Resistance — expected: General GM sensors of this type typically fall in the 200 - 1,000 ohms range.. Failure: A reading of OL (Open Loop/infinite resistance) or a value significantly outside the expected range indicates a failed sensor.
• Sensor Reference Voltage at Connector — expected: 5V ± 0.5V on the reference wire from the TCM with the key on, engine off.. Failure: Missing or low reference voltage points to a problem with the TCM or the wiring, not the sensor itself.
• Sensor Ground Circuit Resistance — expected: Less than 0.1 Ω between the ground pin at the sensor connector and a known good chassis ground.. Failure: High resistance indicates a poor ground connection, which can cause an erratic signal.

Scan Tool Commands That Help

• Tech2 / GDS2: Live Data > Transmission Data > Output Speed Sensor (RPM) — This is the primary diagnostic step after checking for codes. While driving or with wheels spinning safely on a lift, the displayed RPM should be smooth and correlate directly with vehicle speed. An erratic, jumping, or zero reading while the vehicle is moving confirms a fault in the sensor's circuit.

Wiring & Ground Locations

• G106 — On the rear of the engine, above the oil filter (for 3.5L V6).. This is a primary engine/transmission ground point. A corroded or loose connection here can cause a host of intermittent electrical issues for the transmission control module (TCM) and its sensors.
• G105 — Under the left intake manifold, on the rear of the cylinder head.. Another critical engine ground that provides a return path for the TCM. Poor connection here can lead to floating grounds and erratic sensor readings.
• TCM Main Connector — On the 6T70 (V6), the TCM is part of the valve body assembly, located behind the side cover of the transmission. The main external connector is on the top/front of the transmission case.. This is the main interface for all transmission sensors and solenoids. Corrosion or pushed-back pins in this connector can cause a P0720 and other transmission codes. The harness leading to it is a common spot for chafing.

Real Owner Repair Stories

• YouTube channel "T&T Master Mechanics" (2008 Saturn Aura) — Intermittent problem with the speed sensor code. Speedometer would sometimes get stuck at 20 mph, and the vehicle would have no acceleration, requiring full throttle to move. The issue would come and go.
  ❌ Tried (didn't work) Replacing the speed sensor did not fix the problem.
  ✅ What actually fixed it A visual inspection revealed a wiring harness rubbing against the cylinder head, which had worn through the conduit and insulation, causing the wire to ground out intermittently. Additionally, the main ground on the transmission was found to be corroded and was cleaned and repaired. The combination of repairing the chafed wire and cleaning the ground resolved the intermittent issue.

OEM Part Supersession History

• 24223635, 24238337, 24247568, 24247840, 24256878 → 24262388 — Standard part consolidation and potential minor revisions for durability or manufacturing efficiency over the life of the 6T70/6T75 transmission family.
  Heads up: The latest part number, 24262388, is the correct service replacement for all previous numbers on the 2007-2009 Aura with the 6T70 transmission.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• 6T70 Transmission 3-5-R Wave Plate Failure 🔴 High → Shop Transmission Assembly — Very common on V6 models, typically occurring between 60,000 and 120,000 miles. (Ref: GM Special Coverage 14404A / TSB 09-07-30-012F)
• Sudden Loss of Electric Power Steering (EPS) 🔴 High — Common enough to warrant a major safety recall. (Ref: NHTSA Recall 14V153000 (GM Recall N140115))
• Stretched Timing Chains (3.6L LY7 V6) 🔴 High — A well-documented design flaw in early 3.6L V6 engines, often appearing before 100,000 miles. (Ref: GM Special Coverage Program 11340B (for other models with same engine))
• Timing Chain Guide/Tensioner Failure (2.4L Ecotec) 🔴 High — Common failure point, often exacerbated by oil consumption issues. Can lead to catastrophic engine damage.
• Fractured Transmission Shift Cable End Tabs (4-Speed) 🟠 Medium → Shop Transmission Assembly — Widespread enough to cause a safety recall; can prevent shifting into Park. (Ref: NHTSA Recall, mentioned for 2007-2010 models with 4-speed auto.)
• Excessive Oil Consumption (2.4L Ecotec) 🟠 Medium — Common issue related to piston ring design, which can lead to premature timing chain failure if oil level is not monitored closely. (Ref: Subject of a class-action lawsuit leading to extended warranty coverage for some GM vehicles.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this repair, a used part is generally not recommended for the sensor itself due to the high labor cost for replacement on the 6T70 (V6) transmission. However, a used wiring harness pigtail from a junkyard is a very sensible and cost-effective repair if only the connector is damaged.

Donor-vehicle mileage cap: roughly under 100000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For a wiring pigtail, ensure the plastic is not brittle and the locking tab is intact.
• Check for any signs of corrosion on the connector pins.
• Ensure you get at least 6-8 inches of wire to allow for easy splicing.

OEM-only on this vehicle (don't cheap out):

• Output Speed Sensor (for 6T70 V6 models): Given the sensor is internal and requires significant labor to access, using a new OEM (ACDelco) or high-quality OEM-supplier (e.g., Delphi) part is strongly advised to avoid a repeat repair.
• Internal transmission components (e.g., 3-5-R wave plate): If the root cause is internal failure, only new, updated design parts should be used in the rebuild.

Aftermarket brands forum-validated for this vehicle:

• ACDelco (OEM)
• Delphi

Brands owners have reported issues with on this vehicle:

• Unknown, no-name brands from online marketplaces should be avoided for internal transmission electronics due to the high labor cost of failure.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0700 — A general transmission control system malfunction code that often accompanies P0720 when the TCM detects a sensor failure.
• P0008 — Engine positions system performance code related to stretched timing chains, a common co-occurring issue on the 3.6L V6 models mentioned in owner reports.
• P0017 — Crankshaft/Camshaft alignment code often seen alongside transmission issues in high-mileage Auras due to the documented timing chain design flaws.

Frequently Asked Questions