P0720 on 2000-2013 Chevrolet Impala: Output Speed Sensor Causes and Fixes

What's Unique About the 2000-2013 Chevrolet Impala

The 2000-2013 Impala, spanning the 8th and 9th generations, primarily uses the 4T65-E transmission where the Output Speed Sensor is externally mounted and relatively easy to access. The most significant platform-specific issue affects the 9th generation (2006-2013), where the sensor's wiring harness is prone to rubbing against the passenger-side CV axle. This often causes a short circuit, mimicking the symptoms of a failed sensor and making a wiring inspection a mandatory first step in diagnosis.

Generation note: This guide covers the 8th generation (2000-2005) and 9th generation (2006-2013) Impala. Both generations use a similar 4T65-E transmission with an externally located Output Speed Sensor. However, the 9th generation (specifically 2006-2012 models) has a known issue where the sensor's wiring harness can be damaged by rubbing against the CV axle.

Symptoms You May Notice

• Erratic, jumping, or completely dead speedometer
• Harsh, delayed, or unpredictable transmission shifting
• Check Engine Light is illuminated
• Cruise control will not engage or work properly
• Vehicle may enter 'limp mode,' getting stuck in a single gear
• Possible engine stalling when coming to a stop
• Hesitation during acceleration

Most Likely Causes

1. Damaged Output Speed Sensor Wiring Harness 🔴 High Probability On 9th generation models (2006-2013), the wiring harness is routed in a way that it can rub against the passenger-side CV axle, wearing through the insulation and causing a short or open circuit. This is a widely documented failure pattern in owner forums.
   How to confirm: Visually inspect the entire length of the wiring harness leading to the sensor. Look for chafed, melted, or bare wires, particularly where the harness passes near the CV axle. The damage is often found on the underside of the loom. 🎬 Watch: How to repair the damaged wiring harness
   Typical fix: Repair the damaged section of wire using solder and heat-shrink tubing. Secure the harness away from the CV axle using zip ties to prevent future damage.
   Est. part cost: $5-$15 for wire repair supplies
2. Failed Output Speed Sensor (OSS/VSS) 🔴 High Probability The sensor is an electronic component that operates in a high-heat environment (on the transmission housing) and can fail over time due to thermal stress and internal wear.
   How to confirm: After confirming the wiring is intact, test the sensor. Disconnect it and measure its internal resistance with a multimeter. A typical 2-wire sensor for this application should have a resistance between 560 and 680 Ohms. An out-of-spec or infinite reading confirms failure.
   Typical fix: Replace the Output Speed Sensor. It is held in by a single 10mm bolt. 🎬 See this step-by-step speed sensor replacement guide
   Est. part cost: $20-$50
3. Contaminated or Low Transmission Fluid ⚪ Low Probability → Shop Transmission Assembly
   How to confirm: Check the transmission fluid level and condition using the dipstick. If the fluid is dark, burnt-smelling, or contains metallic particles, it indicates a more serious internal transmission issue that could affect sensor operation.
   Typical fix: If the fluid is simply low or old, a transmission fluid and filter change may resolve the issue. If the fluid is heavily contaminated, a transmission rebuild may be necessary.
   Est. part cost: $50-$150 for fluid and filter

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) This is very uncommon. The PCM should only be considered after all other possibilities (sensor, wiring, fluid) have been definitively ruled out.
• Metal Debris on Sensor's Magnetic Tip: Internal transmission wear can cause metallic shavings to stick to the magnetic tip of the speed sensor, disrupting its ability to get a clean reading. The sensor can sometimes be removed, cleaned, and reinstalled to solve the problem temporarily, but this indicates a more severe underlying transmission problem.

Diagnosis Steps

1. Scan the vehicle's computer for any other stored trouble codes to see if P0720 appears with other transmission-related faults.
2. Check the level and condition of the automatic transmission fluid. Burnt or metallic fluid suggests a larger internal problem.
3. Crucial Step for 2006-2013 models: Raise the front passenger side of the vehicle and remove the wheel for access. Thoroughly inspect the wiring harness that connects to the Output Speed Sensor. Check for any signs of rubbing against the CV axle, chafing, or broken wires. This is the most common point of failure for this generation.
4. Inspect the electrical connector at the sensor for corrosion, moisture, or loose pins.
5. If the wiring is confirmed to be in good condition, disconnect the sensor and test its internal resistance using a multimeter. The reading should be between 560-680 Ohms. A reading that is significantly outside this range, or shows an open circuit (infinite resistance), indicates a failed sensor.
6. If possible, use a scan tool with live data capability to monitor the Output Speed Sensor signal while driving. The reading should increase smoothly with vehicle speed. An erratic or absent signal points to a bad sensor or intermittent wiring issue.
7. If the sensor and wiring both test good, the issue may be intermittent or, in rare cases, a problem with the PCM.

Parts You'll Likely Need

• Transmission Output Speed Sensor / Vehicle Speed Sensor (VSS) (OEM #ACDelco 213-4697 (Note: This part number is often associated with EGR temp sensors, cross-reference with VIN is critical. A more common VSS part number for the 4T65E is ACDelco 213-1591 or GM 24227898)) — This sensor is the most common part to fail, leading directly to the P0720 code and its associated symptoms.
  Trusted brands: ACDelco, NGK/NTK, Standard Motor Products, Delphi
  OEM price range: $40-$70
  Aftermarket price range: $20-$50

Related Codes That Often Appear With This One

• P0700 — P0700 is a generic code that means the Transmission Control Module (TCM) has requested the Check Engine Light to be turned on. It often appears alongside more specific transmission codes like P0720.
• P0502 — This code indicates a low input from the Vehicle Speed Sensor (VSS) circuit, which is often the same sensor as the OSS. 🎬 Watch: Understanding P0720 causes and fixes It directly corroborates the P0720 code.
• P0503 — This code points to an intermittent, erratic, or high signal from the VSS circuit, also pointing to the same sensor or wiring fault as P0720.

Platform-Specific Known Issues

• 2006-2013 Models - Wiring Harness Damage: The most common and well-documented issue for this generation is the Output Speed Sensor wiring harness rubbing through on the passenger-side CV axle, causing a short circuit. This should always be the first thing to inspect before replacing parts. Owners on forums like ImpalaForums.com frequently post photos of the exact chafing location as the definitive fix.
• Owner Experience: A common repair story involves a 2008 Impala owner who replaced the OSS twice with no change in symptoms. After finding a forum thread, they inspected the harness near the CV axle and found two wires rubbed bare. A simple wiring repair and securing the harness with a zip tie permanently solved the P0720 code and shifting issues.

Mechanic-Grade Diagnostic Values

• Output Speed Sensor (VSS) Internal Resistance — expected: 981-1864 Ohms. Failure: A reading of infinite resistance (open circuit), zero resistance (short circuit), or a value significantly outside the specified range.

Scan Tool Commands That Help

• GDS2/Tech2 or equivalent professional scan tool: Live Data - Transmission Output Speed — This is a primary diagnostic step. While driving, the Output Speed Sensor PID should display a smooth, consistently increasing speed that directly correlates with the vehicle's actual speed. Erratic jumps, dropouts to zero, or no reading at all while the vehicle is in motion strongly indicates a fault in the sensor or its circuit.

Wiring & Ground Locations

• VSS Connector — On the transaxle housing, typically accessed from the passenger side wheel well, near where the CV axle enters the transmission.. This is the direct connection point for the sensor. Corrosion, moisture, or spread pins in this connector can cause the same symptoms as a failed sensor.
• G111 — Located on a transmission-to-engine bolt, often above the starter.. This is a primary ground point for multiple engine and transmission components. A loose or corroded G111 can introduce electrical noise or cause an unstable ground reference for sensors like the VSS, leading to erratic signals.

Model Year Variations Within This Range

• 2006-2013: The wiring harness routing was changed in a way that puts it in close proximity to the passenger-side CV axle. This creates the common chafe point that is the number one cause of P0720 on these later models. The sensor itself and its function remained the same across the 2000-2013 range.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Intake Manifold Gasket Failure (3.8L V6) 🔴 High — Extremely common on the 3.8L Series II engine (2000-2005 models), often failing between 80,000 and 150,000 miles. Can lead to coolant leaks, overheating, and catastrophic engine damage if coolant mixes with oil.
• Transmission Pressure Control Solenoid (PCS) Failure 🔴 High → Shop Transmission Valve Body — A well-known weak point in the 4T65-E transmission across all model years. Failure leads to harsh shifting, delayed engagement, and can set codes like P1811. Often requires partial transmission disassembly to replace.
• Intermediate Steering Shaft Clunk 🟡 Low — Very common across both generations. A clunking or popping noise is heard and felt through the steering wheel during low-speed turns. The typical fix is to lubricate or replace the intermediate steering shaft. (Ref: TSB #00-02-35-003E)
• Passlock Security System Failure 🟠 Medium — Common on 2000-2005 models. The system can fail to recognize the key, causing a no-start condition where the 'Security' light flashes on the dashboard. Often requires a 10-minute relearn procedure or replacement of the ignition switch.
• Power Window Regulator Failure 🟡 Low — Frequent problem where the window may become slow, get stuck, or drop into the door. Caused by a failure of the plastic components within the regulator assembly.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used wiring harness pigtail from a junkyard is an excellent and cost-effective choice, especially if the original connector is damaged or you need to repair a section of the harness. A used sensor is a viable option if it comes from a low-mileage donor and has a warranty, but new aftermarket sensors are inexpensive enough that they are often the better choice.

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 connector isn't brittle or cracked.
• Check for clean, corrosion-free electrical pins inside the connector.
• Inspect the wires for at least 6-8 inches of flexible, undamaged insulation.
• For a used sensor, check that the magnetic tip is clean and free of heavy metallic sludge, which could indicate the donor transmission had internal issues.

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

• For this repair, there are no components that are strictly 'OEM-only'. Quality aftermarket sensors perform well.

Aftermarket brands forum-validated for this vehicle:

• ACDelco (OEM)
• Delphi
• Standard Motor Products (SMP)
• NTK

Brands owners have reported issues with on this vehicle:

• Ultra-low-cost, unbranded sensors from online marketplaces can have high failure rates and should be avoided for this critical sensor.

Real Owner Stories

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

Related OBD-II Codes

• P1811 — Often appears in conjunction with transmission issues on the 4T65-E platform; specifically related to the Transmission Pressure Control Solenoid (PCS) failure which causes harsh shifting.
• P0700 — A general transmission control system malfunction code that may be stored alongside P0720 when the PCM detects erratic signals from the Output Speed Sensor.

Frequently Asked Questions